Wufeng, along with neighboring townships such as Xinshe in Taichung, is the heartland of mushroom cultivation in <a href="https://www.atlasobscura.com/things-to-do/taiwan">Taiwan</a>
The region is known for its innovation in mushroom farming
including the invention of the modern "space bags," a technique that revolutionized mushroom cultivation by allowing more efficient and controlled growth
The Wufeng Mushroom Museum is housed in a regular office building of the Wufeng Farmers' Association
with an unassuming exterior that hides a surprisingly rich and immersive experience inside
The museum claims to be one of only two mushroom museums in the world, alongside the Museum De Locht in the Netherlands. However, similar institutions exist, like the <a href="https://www.atlasobscura.com/places/museum-of-mushrooms">Museum of Mushrooms</a>&nbsp;in Zagreb and Austria’s Pilz Museum
the Wufeng Mushroom Museum remains a comprehensive space dedicated to mushrooms.&nbsp;
Among the rare specimens on display is the caterpillar fungus, a parasitic <a href="https://www.atlasobscura.com/categories/fungus">fungus</a> that infects insects
and eventually sprouts from the insect's head—a prized medicinal fungi in traditional Chinese medicine
One of the most intriguing exhibits is an interactive sound installation demonstrating how fungi generate electrical signals
Inspired by research suggesting that fungi use mycelial networks to transmit information—akin to a neural system—scientists have recorded electrical pulses from fungi and converted them into sound waves
Visitors can attach sensors to live fungi and listen as the mushrooms "communicate" through a melodic hum
Admission is NT$100 (~$3 USD) for adults and NT$50 for children
One of the oldest universities in the world exhibits thousands of specimens from its 700-year-old collection
This 19th-century zoological collection has withstood the test of time
This enthusiast-led facility is the only museum in the country dedicated to the preservation of weather artifacts
A treasure trove of scientific instruments from the 17th and 18th centuries
and odd collections of generations of college professors
A small museum packed with specimens from important fossil sites and minerals from historical pegmatite quarries
This exhibit pays tribute to the “humble tinkerer” who invented the implantable pacemaker
The old castle kitchen where nucleic acid was first isolated is considered the &quot;cradle of biochemistry.&quot; 
<a href="/articles/s41598-024-84415-y/metrics" data-track="click" data-track-action="view metrics" data-track-label="link" rel="nofollow">Metrics details</a>
and LY2 in the Laifeng–Xianfeng area as the research target
the characteristics of graptolite zone development
shale reservoir properties and the gas-bearing properties of the Wufeng–Longmaxi Formation shale are systematically analyzed
The main factors affecting the gas-bearing capacity of the Wufeng–Longmaxi Formation shale are extensively evaluated
The results reveal the following: ① The Wufeng–Longmaxi Formation shale
which was deposited in a deep-water shelf environment
has a large thickness (50–60 m) and a stable distribution
The lower segment of the Wufeng–Longmaxi Formation shale is rich in graptolite fossils
and the thickness of the WF2–LM4 graptolite zone
which is the most favorable segment for shale gas development
which is relatively thinner than the 25 m of well JY1
② Wufeng-Longmaxi formation shale has characteristics of a high organic carbon content
the thickness of the organic-rich shale section is relatively thin (10–15 m)
and has developed organic pores and microfractures as reservoirs; thus
the physical properties of the reservoir are characterized by a low porosity and ultralow–low permeability
On the basis of a comprehensive evaluation
the shale has the necessary conditions for gas enrichment
③ The Langmuir volume of core samples from different wells located in different structural parts is relatively high
while the gas content obtained from field desorption was quite different
The gas content of well LD1 (0.23–3.73 m3/t) and well LY2 (0.47–2.38 m3/t) located at the core of the Lianghekou syncline was greater than that of well LD2 (0.04–0.72 m3/t) located at the wing of the same syncline
The gas content of well LY2 located in the syncline core has characteristics that indicate significant changes in the longitudinal profile
and the gas content was much lower than that of well LD1
which is also located in the syncline core
④ The high-quality material basis was the basic condition
and the good preservation conditions were the key factors for the high gas content of the Wufeng–Longmaxi Formation shale
The high-angle fractures and fracture zones formed by the NW high-angle strike-slip faults in the Laifeng–Xianfeng area are the main factors influencing the differences in the gas content of the shale in the different structural parts
relatively few systematic studies have investigated the factors that influence the shale gas-bearing characteristics of the Wufeng–Longmaxi Formations in the Laifeng–Xianfeng area
on the basis of the drilled parameter wells LD1 (located in the axial part of the Lianghekou syncline) and well LD2 (located in the southeastern wing of the Lianghekou syncline)
as well as the exploratory well LY2 (located in the core part of the Lianghekou syncline) in the different tectonic parts of the Laifeng–Xianfeng area
the necessary conditions for shale gas enrichment
and the gas-bearing influencing factors of the Wufeng–Longmaxi Formation are discussed
tectonic outline (b) and lithological column (c) in the Laifeng–Xianfeng area
</a>Sedimentary facies map of the O3w – S1l shale
A total of 146 Wufeng–Longmaxi shale samples from the drilled cores of wells LD1, LD2, and LY2 and 45 shale samples from outcrops were collected and tested to analyze their organic geochemical characteristics, mineral compositions, reservoir characteristics, and gas-bearing properties (Fig. <a data-track="click" data-track-label="link" data-track-action="figure anchor" href="/articles/s41598-024-84415-y#Fig1">1</a>)
In a detection environment with a temperature of 22 °C and a humidity of 40% RH
the whole-rock mineral and clay mineral compositions of the 146 samples were comprehensively and quantitatively measured via X-ray diffraction (XRD) in accordance with the Chinese Oil and Gas Industry Standard SY/T 5163-2010
The pore structures of 3 wells were measured by scanning electron microscopy (SEM) following the standard of SY/T 5162-2014
and fractures of different sizes were identified
with magnifications ranging from 1000 to 80,000
The porosity and permeability of 140 shale samples from 3 wells were measured using the pulse method with a Poro PDP-200 overburden porosity and permeability tester
a 3D scanner was used to measure the porosity and permeability; the reference standard is GB/T29172-2012
the analytical gas volume obtained from the analysis after the sample canning
and the residual gas volume remaining in the core determined by grinding the core at a high temperature after terminating the analysis
23 samples were subjected to high-pressure isothermal adsorption experiments following the standard GB/T 19560-2008
The lithology of the lower section of the Wufeng–Longmaxi Formation is grayish black–black shale
and the bottom siliceous rock contains abundant subdeep water radiolaria
The middle section is composed of dark gray blocky mudstone or shaly siltstone
The upper section is mainly dark gray–gray black carbonaceous shale intercalated with carbonaceous shaly siltstone
with the development of horizontal bedding and is rich in graptolite fossils
</a>Comparison histogram of the WF2–LM4 graptolite zones in wells JY1 and LD1
The calculated TI values in Laifeng–Xianfeng area ranges from 36 to 54.5
with only two samples from well LD1 having a kerogen TI less than 40
A comprehensive estimation revealed that the kerogen type of the Wufeng–Longmaxi shale was type II1
</a>Comparison histogram of the reservoir characteristics and gas content of the O3w–S1l shales in wells LD1
The Ro values of 11 shale samples in well LD1 range from 2.79 to 3.32%
with an average of 3.11%; those of the 10 samples in well LD2 range from 1.47 to 2.63%
with an average of 1.96%; and those of the 4 samples in well LY2 range from 2.55 to 3.06%
suggesting that the Wufeng–Longmaxi shale was in an overmature stage with predominantly dry gas generation
The distribution of Ro is stable in the vertical direction
the Wufeng–Longmaxi shale was dominated by quartz and clay minerals
The results of the field outcrop samples revealed that the content of quartz + feldspar ranged from 45 to 73%
The quartz + feldspar content of well LD1 ranges from 24.0 to 71.2%
the clay mineral content ranges from 17.8 to 60.2%
whereas that of well LD2 ranges from 37.4 to 65.3%
the clay mineral content ranges from 14.7 to 50.3%
and that of well LY1 ranges from 23 to 68.4%
the clay mineral content ranges from 20.6 to 61.6%
The average content of carbonate minerals in the three wells are 7.0%
The lateral distributions of the mineral compositions are basically equal (Fig. <a data-track="click" data-track-label="link" data-track-action="figure anchor" href="/articles/s41598-024-84415-y#Fig4">4</a>)
indicating that the sedimentary environment of the Wufeng–Longmaxi Formation in the Laifeng–Xianfeng area was stable
and that the basis of hydrocarbon generation materials was consistent
the content of brittle minerals (quartz and feldspar) is slightly greater in the bottom section of the Wufeng–Longmaxi Formation
and the brittle mineral content in well LD1 is 43–69%
The brittle mineral content of the middle and lower Sects
(20–25 m) slightly decrease compared with that of the bottom section
and the content of quartz and feldspar are relatively high
The upper section has the highest content of brittle minerals in the Wufeng–Longmaxi Formations
has the lowest content of brittle minerals
Fracturing treatment is easy for Wufeng–Longmaxi shale reservoirs because of their brittleness characteristics
</a>Frequency statistics of the pore and fracture types in well LD1
</a>Distribution of pores and fractures in the O3w–S1l shale in well LY2
(a: 2063.50 m; b: 2067.65 m; c: 2075.54 m; d: 2091.25 m; e: 2095.70 m; f: 2099.68 m; g: 2103.09 m; h: 2109.70 m; i: 2113.25 m)
micropores and mesopores are the main spaces for natural gas occurrence in the Wufeng–Longmaxi shale
The physical properties of the Wufeng–Longmaxi shale samples tested via the pulse-decay method revealed that the porosity of well LD1 ranged from 0.06 to 2.09%, with an average value of 0.73% (Fig. <a data-track="click" data-track-label="link" data-track-action="figure anchor" href="/articles/s41598-024-84415-y#Fig3">3</a>)
and those of wells LD2 and LY2 ranged from 0.0056 to 1.26% and 0.035–1.83%
Nearly 50% of the total samples from well LD1 have a porosity less than 1.0%
whereas 98% and 90% of the samples from well LD2 and well LY2 have porosities less than 1.0%
The Wufeng–Longmaxi shale is an ultralow-porosity shale reservoir
The permeability of the shale samples from well LD1 ranged from 0.00003 to 0.6 mD
with the main distribution ranging from 0.001 to 0.01 mD
The permeability of well LD2 is 0.00014–0.0095 mD
and 93% of the samples have permeabilities less than 0.001 mD
The permeability of well LY2 is 0.00008–1.46 mD
and more than 60% of the samples have permeabilities greater than 0.001 mD
the permeabilities of wells LD1 and LY2 are greater than that of well LD2
which adequately reveals that in areas with stable sedimentation
there are significant changes in porosity and permeability due to the influence of reservoir reconstruction after sedimentation
The reason for the high permeabilities of wells LD1 and LY2 is that the bedding fractures are well developed
and they are conducive to the lateral migration of shale gas
Compared with the shale reservoir properties of commercial exploitation in North America
the reservoir properties of Wufeng–Longmaxi shale in the Laifeng–Xianfeng area are characterized by ultralow porosity corresponding to relatively high permeability
indicating that the extensive development of microfractures provides a suitable storage space and infiltration channels for shale reservoirs
The results of the isothermal adsorption experiments reveal that the Langmuir volume (VL) of well LD1 ranges from 1.64 to 2.79 m3/t, with an average value of 2.31 m3/t, whereas that of well LD2 ranges from 3.01 to 5.15 m3/t, with an average value of 4.10 m3/t, and that of well LY2 ranges from 1.77 to 3.80 m3/t, with an average value of 2.78 m3/t (Table <a data-track="click" data-track-label="link" data-track-action="table anchor" href="/articles/s41598-024-84415-y#Tab1">1</a>)
The samples with larger Langmuir volumes in the three wells are all present in the lower part of the Wufeng–Longmaxi shale
These results indicate that the Wufeng–Longmaxi shale has a strong adsorption capacity for methane
</a>Comparison of desorption gas content under different temperature conditions in well LY2
The field desorption gas content (VDG) of 17 samples from well LD2 ranges from 0.04 to 0.71 m3/t
with an average of 0.20 m3/t; the lost gas content (VLG) ranges from 0 to 0.25 m3/t
The residual gas content (VRG) ranges from 0 to 0.25 m3/t
and the total gas content ranges from 0.02 to 1.28 m3/t
The field desorption gas content of well LY2 ranges from 0.02 to 1.28 m3/t
The lost gas content (VLG) ranges from 0.38 to 1.38 m3/t
The total gas content (VTG) ranges from 0.47 to 2.38 m3/t
Vertically, the layer with higher gas content is located at the bottom of the Wufeng–Longmaxi shale, and its thickness is relatively thin. The thickness of the high-quality shale layer with a gas content greater than 2.0 m3/t is only 4 m in well LY2, 21 m in well LD1, and 0 m in well LD2 (Fig. <a data-track="click" data-track-label="link" data-track-action="figure anchor" href="/articles/s41598-024-84415-y#Fig3">3</a>)
The shale section with a relatively high gas content developed within the WF2–LM4 graptolite zone
The characteristics of the Wufeng–Longmaxi shale in well LD2 were similar to those in well LD1
The shale section with a relatively high gas content developed in the lower part was composed of black siliceous shale and gray–black argillaceous shale
Comparing the differences in lithology between the upper and lower parts of the Wufeng–Longmaxi shale
the organic shale enriched with graptolite fossils has better gas-bearing properties
</a>Correlations between the TOC content and total gas content
The specific surface area available for natural gas adsorption increases sharply
and the content of adsorbed gas and free gas in shale also increase
The field desorption gas content in the microfracture development section of the Wufeng–Longmaxi shale in well LD1 can reach 1.65 m3/t
The reason for the low gas content is the well-developed bedding fractures in well LY2
which take a long time in the coring process and result in gas escaping
the lower porosity of the shale in well LY2 corresponds to a higher permeability
which is 100 times greater than that in well LD1
which is the reason why the field desorption gas content in well LY2 is lower than that in well LD1
the more developed the organic pores and microfractures are
The Wufeng–Longmaxi shale is a typical tight reservoir with poor porosity and permeability
The relationships between gas content and porosity and permeability in the three wells are poor
</a>Comparison diagram of roof-to-floor ratios of the O3w–S1l shales in wells LD1
</a>Structural profile of a seismic interpretation in the Laifeng–Xianfeng area
</a>Logging images and core images of the O3w–S1l shale at depths of 2080–2110 m in well LY2
The Wufeng–Longmaxi shale in the Laifeng–Xianfeng area was deposited in a deep-water shelf environment of clastic rock
The lower part of the shale is rich in graptolite fossils
with high TOC content and degrees of thermal evolution
The organic-rich shale section is relatively thin
The mineral composition is mainly quartz and clay minerals
The storage space is mainly composed of organic pores and microfractures
with slight differences in the physical properties of the reservoirs at different structural locations
the area has the characteristics of low porosity and ultralow permeability
with good shale quality and shale gas accumulation conditions
The VL of the wells drilled at different structural locations are relatively high and roughly equivalent
indicating that the Wufeng–Longmaxi shale has a high methane adsorption capacity
the field desorption gas content in different structural parts varies significantly
which are located in the core of the Lianghekou syncline
The organic-rich shale with a total gas content greater than 2.0 m3/t developed in the bottom part of the Wufeng–Longmaxi Formation
The field desorption gas content in the deep-water shelf sedimentary environments is greater than that in the shallow-water shelf sedimentary environments
and a relatively high gas content corresponds to a relatively high TOC content
The more developed the organic matter pores and microfractures are
whereas the correlation between the reservoir physical properties and gas content is poor
high-quality material is the foundation for the high gas content of the Wufeng–Longmaxi shale
and good preservation conditions are the key to high gas content
The high-angle fractures and fault fracture zones formed by the northwest-trending high-angle strike-slip faults in the Laifeng–Xianfeng area are a substantial cause of the differences in the shale gas content in the different structural locations
The data that support the findings of this study are available from the corresponding author upon reasonable request
An analysis of geological structure factor behind the high productivity of fuling shale gas field and some thoughts
Jin, Z. J., Hu, Z. Q., Gao, B. &amp; Zhao, J. H. Controlling factors on the enrichment and high productivity of shale gas in the Wufeng-Longmaxi formation, southeastern Sichuan Basin. Earth Sci. Front. 23(1), 1–10. <a href="https://doi.org/10.13745/j.esf.2016.01.001" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.13745/j.esf.2016.01.001">https://doi.org/10.13745/j.esf.2016.01.001</a> (2016)
Guo, X. S. et al. Geological factors controlling shale gas enrichment and high production in Fuling Shale gas field. Pet. Explor. Dev. 44(4), 481–491. <a href="https://doi.org/10.11698/PED.2017.04" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.11698/PED.2017.04">https://doi.org/10.11698/PED.2017.04</a> (2017)
Investigation and evaluation of shale gas resource potential in China (Geol
Ultra-low water saturation characteristics and the identification of over-pressured play fairways of marine shales in south China
Jiang, S. L. et al. Shale gas accumulation conditions and gas-bearing infuencing factors of Lower Cambrian Niutitang formation in Western Hunan and Hubei area. Mar. Origin Pet. Geol. 23(1), 75–82. <a href="https://doi.org/10.3969/j.issn.1672-9854.2018.01.009" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.3969/j.issn.1672-9854.2018.01.009">https://doi.org/10.3969/j.issn.1672-9854.2018.01.009</a> (2018)
Jiang, S. L. et al. Characteristics and gas content of Wufeng-Longmaxi formation shale in the well LD2 of the Laifeng-Xianfeng block. Geol. Explor. 54(1), 203–210. <a href="https://doi.org/10.13712/j.cnki.dzykt.2018.01.022" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.13712/j.cnki.dzykt.2018.01.022">https://doi.org/10.13712/j.cnki.dzykt.2018.01.022</a> (2018)
Wang, X. P., Mou, C. L., Xiao, Z. H., Chen, Y. &amp; Wang, Q. Y. Petrologic characteristics and genesis analysis of the Ordovician Wufeng formation-silurian Longmaxi formation in Laifeng-Xianfeng area of western Hubei. Oil Gas Geol. 40(1), 50–66. <a href="https://doi.org/10.11743/ogg20190106" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.11743/ogg20190106">https://doi.org/10.11743/ogg20190106</a> (2019)
Li, B. et al. Evaluation and understanding on the shale gas wells in complex tectonic provinces outside Sichuan Basin, South China: a case study from well Laiye 1 in Laifeng-Xianfeng Block, Hubei. Nat. Gas. Ind. 36(8), 29–35. <a href="https://doi.org/10.3787/j.issn.1000-0976" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.3787/j.issn.1000-0976">https://doi.org/10.3787/j.issn.1000-0976</a> (2016)
Liu, X. L. et al. The geological characteristics and resource potential of shale gas of Wufeng-Longmaxi formation in Laifeng- Xianfeng block, Hubei Province. Mar. Origin Pet. Geol. 25(4), 344–350. <a href="https://doi.org/10.3969/j.issn.1672-9854.2020.04.007" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.3969/j.issn.1672-9854.2020.04.007">https://doi.org/10.3969/j.issn.1672-9854.2020.04.007</a> (2020)
Li, J. et al. Shale pore characteristics and their impact on the gas-bearing properties of the Longmaxi Formation in the Luzhou area.Sci. Rep. 14(1), 16896. <a href="https://doi.org/10.1038/S41598-024-66759-7" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.1038/S41598-024-66759-7">https://doi.org/10.1038/S41598-024-66759-7</a> (2024)
Formation stages and evolution patterns of structural fractures in marine shale: case study of the lower silurian Longmaxi Formation in the Changning area of the southern Sichuan basin
Fan, C. H., Li, H., Qin, Q. R., He, S. &amp; Zhong, C. Geological conditions and exploration potential of shale gas reservoir in Wufeng and Longmaxi formation of southeastern Sichuan Basin, China. J. Petrol. Sci. Eng. 191, 107138. <a href="https://doi.org/10.1016/j.petrol.2020.107138" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.1016/j.petrol.2020.107138">https://doi.org/10.1016/j.petrol.2020.107138</a> (2020)
Hu, H. Y. et al. Organic matter-hosted pore system in the Wufeng-Longmaxi (O3w-S1l) shale, Jiaoshiba area, eastern Sichuan basin, China. Int. J. Coal Geol. 173(15), 40–50. <a href="https://doi.org/10.1016/j.coal.2017.02.004" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.1016/j.coal.2017.02.004">https://doi.org/10.1016/j.coal.2017.02.004</a> (2017)
Xiong, J., Liu, X. J. &amp; Liang, L. X. Experimental study on the pore structure characteristics of the upper ordovician wufeng formation shale in the southwest portion of the Sichuan basin, China. J. Nat. Gas Sci. Eng. 22, 530–539. <a href="https://doi.org/10.1016/j.jngse.2015.01.004" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.1016/j.jngse.2015.01.004">https://doi.org/10.1016/j.jngse.2015.01.004</a> (2015)
New understandings of the factors controlling of deep shale gas enrichment in the Wufeng formation-longmaxi formation of the southern Sichuan basin
Cui, X. X. et al. Gas-bearing characteristics and main controlling factors of deep shale in Longmaxi Formation in Weirong area, Sichuan Basin.Nat. Gas Geosci. <a href="https://link.cnki.net/urlid/62.1177.TE.20240711.1456.004" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="https://link.cnki.net/urlid/62.1177.TE.20240711.1456.004">https://link.cnki.net/urlid/62.1177.TE.20240711.1456.004</a>  (2024)
Shale gas-bearing capacity and its controlling factors of Wufeng-Longmaxi formations in northern Guizhou
Structural characteristics and shale gas explora tion potential in Southeast Sichuan-Western Hubei and Hunan areas
Wuhan: China University of Geosciences Press.1-124 (2011)
Jiang, S. L. et al. Fracability evaluation of shale reservoir in the lower Cambrian Niutitang formation of well HY1, northwestern, Hunan. Geoscience 35(4), 1024–1032. <a href="https://doi.org/10.19657/j.geoscience.1000-8527.2021.055" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.19657/j.geoscience.1000-8527.2021.055">https://doi.org/10.19657/j.geoscience.1000-8527.2021.055</a> (2021)
Nie, H. K., Zhang, J. C., Bao, S. J., Song, X. J. &amp; Liu, J. B. Shale gas accumulation conditions of the Upper Ordovician-Lower Silurian in Sichuan Basin and its periphery. Oil Gas Geol. 33(3), 335–345. <a href="https://doi.org/10.11743/ogg20120302" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.11743/ogg20120302">https://doi.org/10.11743/ogg20120302</a> (2012)
Chen, K. et al. Main controlling factors on shale adsorption capacity of the Lower Silurian Longmaxi formation in western Hunan-Hubei area. Oil Gas Geol. 37(1), 23–29. <a href="https://doi.org/10.11743/ogg20160104" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.11743/ogg20160104">https://doi.org/10.11743/ogg20160104</a> (2016)
Chen, X. et al. Late ordovician to earliest silurian graptolite and brachiopod biozonation from the Yangze region, South China, with a global correlaition. GeoScience World 137(6), 623–650. <a href="https://doi.org/10.1017/s0016756800004702" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.1017/s0016756800004702">https://doi.org/10.1017/s0016756800004702</a> (2000)
Biostratigraphy of the Wufeng - Lungmachi black shales at Qilin
Subdivision and delineation of the Wufeng and Lunmachi black shales in the subsurface areas of the Yangtze platform
Zou, C. N. et al. Shale gas in China: characteristics, challenges and prospects (I). Pet. Explor. Dev. 42(6), 689–701. <a href="https://doi.org/10.11698/PED.2015.06.01" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.11698/PED.2015.06.01">https://doi.org/10.11698/PED.2015.06.01</a> (2015)
Zou, C. N. et al. Shale gas in China: characteristics, challenges and prospects (II). Pet. Explor. Dev. 43(2), 166–178. <a href="https://doi.org/10.11698/PED.2016.02.02" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.11698/PED.2016.02.02">https://doi.org/10.11698/PED.2016.02.02</a> (2016)
Nie, H. K. &amp; Jin, Z. J. Source rock and cap rock controls on the upper Ordovician Wufeng formation -lower silurian Longmaxi formation shale gas accumulation in the Sichuan Basin and its peripheral areas. Acta Geol. Sin. 90(3), 1059–1060. <a href="https://doi.org/10.1111/1755-6724.12752" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.1111/1755-6724.12752">https://doi.org/10.1111/1755-6724.12752</a> (2016)
Nie, H. K., Jin, Z. J., Bian, R. K. &amp; Du, W. The source-cap hydrocarbon-controlling enrichment of shale gas in Upper Ordovician Wufeng formation - lower silurian Longmaxi formation of Sichuan Basin and its periphery. Acta Pet. Sin. 37(5), 557–571. <a href="https://doi.org/10.7623/SYXB201605001" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.7623/SYXB201605001">https://doi.org/10.7623/SYXB201605001</a> (2016)
Zhang, P. X. et al. Geological characteristics and enrichment model of Permian Mao 1 Member Shale gas reservoirs in Nanchuan area. Nat. Gas Ind. B 9(1), 96–105. <a href="https://doi.org/10.1016/J.NGIB.2021.12.002" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.1016/J.NGIB.2021.12.002">https://doi.org/10.1016/J.NGIB.2021.12.002</a> (2022)
Nie, H. K. et al. Graptolites zone and sedimentary characteristics of Upper Ordovician Wufeng formation - lower silurian Longmaxi formation in Sichuan basin and its adjacent areas. Acta Pet. Sin.  38(2), 160–174. <a href="https://doi.org/10.7623/syxb201702004" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.7623/syxb201702004">https://doi.org/10.7623/syxb201702004</a> (2017)
Identifcation of microcomponents and types of kerogen under transmitted light
Wu, J. F. et al. Fracture characteristics of the Longmaxi formation shale and its relationship with gas-bearing properties in Changning area, southern Sichuan. Acta Geol. Sinica. 42(4), 428–446. <a href="https://doi.org/10.7623/syxb202104002" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.7623/syxb202104002">https://doi.org/10.7623/syxb202104002</a> (2021)
Shale gas enrichment model and exploration implications in the mountainous complex structural area along the southwestern margin of the Sichuan Basin: a new shale gas area
Fu, Y. H. et al. Microscopic pore-fracture configuration and gas-filled mechanism of shale reservoirs in the western Chongqing area, Sichuan Basin, China. Pet. Explor. Dev. 48(5), 916–927. <a href="https://doi.org/10.11698/PED.2021.05.04" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.11698/PED.2021.05.04">https://doi.org/10.11698/PED.2021.05.04</a> (2021)
Ross, D. J. K. &amp; Bustin, R. M. The importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs. Mar. Pet. Geol. 26, 916–927. <a href="https://doi.org/10.1016/j.marpetgeo.2008" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.1016/j.marpetgeo.2008">https://doi.org/10.1016/j.marpetgeo.2008</a> (2009)
Suggestions from the development of fractured shale gas in North America
Guo, W. X. et al. Characteristics of structural deformation in the southern Sichuan Basin and its relationship with the storage condition of shale gas. Nat. Gas. Ind. 41(5), 11–19. <a href="https://doi.org/10.3787/j.issn.1000-0976.2021.05.002" data-track="click_references" data-track-action="external reference" data-track-value="external reference" data-track-label="10.3787/j.issn.1000-0976.2021.05.002">https://doi.org/10.3787/j.issn.1000-0976.2021.05.002</a> (2021)
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This research was funded by the Natural Science Foundation of Gansu Province
the Industry Support Plan for University of Gansu Province
the Special Project of Science and Technology Specialist
the Innovation Foundation of Higher Education in Gansu Province
the Young Talents (Team) Project in 2025 of Gansu Province
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Volume 12 - 2024 | <a class="ArticleLayoutHeader__info__doi" href="https://doi.org/10.3389/feart.2024.1457377">https://doi.org/10.3389/feart.2024.1457377</a>
The sedimentary environment and organic matter (OM) accumulation are vital indicators for shale gas exploration
research on deep shale gas systems is relatively limited; moreover
the exploration of deep shale gas in the southeastern Sichuan Basin has entered a period of stagnation
systematic geochemical analysis of Wufeng (WF) and the first member of the Longmaxi (Long-1) deep shale samples from the recently drilled DY7 well in the Dingshan area of the Sichuan Basin is carried out
and the longitudinal variations in major and trace elements are revealed
lower section of the Long-1 (Long-11) and upper section of the Long-1 (Long-12) shales are studied in terms of redox conditions
and the different main controlling factors of OM accumulation for these three layers are discussed
The WF shale has a higher TOC content (mean: 5.73%)
the Long-11 shale has a high TOC content (mean: 2.89%)
while the Long-12 shale has a low TOC content (mean: 1.44%)
due to complex geological events and large fluctuations in element contents
its TOC content is poorly correlated with these indices
redox and paleoproductivity proxies have a positive association with the Long-11 shale&#x02019;s TOC content
but negatively correlated with terrigenous input and sedimentation rate indices
The formation of these two sets of organic-rich shales (TOC &#x0003e; 2%) is jointly controlled by good preservation conditions
the TOC content of the WF shale is higher than that of the Long-11 shale as the result that terrigenous input and sedimentation rate of the Long-11 shale represent the dilution and destruction of OM
the water column experienced weak reducing conditions and low productivity
and its high terrigenous debris input further diluted the OM
Recently, geochemical studies have been carried out on the WF-LMX shale. Current studies have suggested that the environmental contexts of the Late Ordovician and Early Silurian were different (<a href="#B90">Zou et al., 2019</a>)
The paleoenvironment is the material basis that controls petroleum generation and accumulation in marine shale systems
there are few studies on the differences and mechanisms of OMA in deep reservoirs between the WF and LMX shales
fresh core collected from recent shale gas exploration wells in the Dingshan area are selected to systematically investigate the three parts
The objectives of this study are summarized as follows: (a) To determine how various environmental factors are reconstructed
and upwelling on OMA are studied in detail
(b) To identify the differences and mechanisms of OMA in two sets of high-quality shales
These results provided new perspectives on the exploration and development potential of deep shale gas in the Sichuan Basin
Figure 1. (A) Geological map of the Sichuan Basin and geographical location map of the study area (modified from <a href="#B51">Nie et al., 2023</a>). (B) Stratigraphic column of the Wufeng-Longmaxi formations in the Sichuan Basin (modified from <a href="#B72">Wang H. Y. et al., 2022</a>)
The Dingshan area is in the southeastern Sichuan Basin. The region experienced tectonic uplift during the Caledonian and burial during the Hercynian-Indian movement, as well as folding and rupture during the Yanshan-Himalayan movement (<a href="#B11">Cao et al., 2021</a>). The present-day tectonics of the Dingshan area consist of a series of steep backslopes and fracture zones trending NE and NNE that are trough folds (<a href="#B26">Huang et al., 2011</a>)
The samples were crushed and sieved through a sieve of less than 200 mesh
150 mg of each powdered sample was weighed and then removing carbonate minerals
The TOC contents were determined using a LECO CS230 analyzer
The major element tests were carried out by an X-ray fluorescence spectrometer (instrument model: AXios-mAX). The 200 mesh powdered samples were dried at 105&#x000b0;C for 2&#x02013;3 h. First, 0.7 g of each sample and 7 g of Li2B4O7 reagent were weighed and mixed, and then melted at 1,150&#x000b0;C to form a glass slice, which was then tested on an X-fluorescence spectrometer. An analytical precision was better than &#x000b1;5% (<a href="#B63">Tan et al., 2021</a>)
The trace and rare earth elements contents of the samples were testing by was an ICP-MS (instrument model: ICAP RQ). An analytical precision was better than &#x000b1;10%. The detailed analysis is described in the references (<a href="#B82">Yang, et al., 2021</a>; <a href="#B23">He et al., 2022</a>)
The enrichment factors (EF) can be used to evaluate the enrichment degree of trace elements in shales (<a href="#B8">Algeo and Tribovillard, 2009</a>). The calculation formula of EF (<a href="#B76">Wedepohl, 1971</a>) is as <a href="#e1">Equation 1</a>:
where, X is the trace element content of the shale sample, and PAAS is a standard shale reference based on the Post-Archean Australian Shale (<a href="#B65">Taylor and McLennan, 1985</a>)
XEF &#x0003e; 1 indicates that the shale sample is more enriched in element X relative to the PAAS
The chemical index of alteration (CIA) is a reliable indicator for assessing chemical weathering intensity (<a href="#B45">McLennan et al., 1993</a>; <a href="#B38">Lu et al., 2024</a>), reflecting the paleoclimate evolution of the sedimentary source area, and the CIA is calculated as <a href="#e3">Equation 3</a> (<a href="#B48">Nesbitt and Young, 1982</a>; <a href="#B38">Lu et al., 2024</a>)
The chemical formula for oxides is in moles, CaO&#x0002a; refers to CaO in silicate minerals, and non-silicate minerals should be removed in the calculation, the formula for CaO&#x0002a; is as <a href="#e4">Equations 4</a>, <a href="#e5">5</a> (<a href="#B45">McLennan et al., 1993</a>):
The TOC contents of the studied shale samples are shown in <a href="#SM1">Supplementary Table S1</a>. In general, the TOC contents show a gradually decreasing trend from bottom to top, but the variations in the different layers differed (<a href="#F2">Figure 2</a>)
The TOC contents of the WF shale are higher
which shows significant longitudinal fluctuations
The TOC contents of the Long-11 shale are high
and show an obvious gradually decreasing trend
The TOC contents of the Long-12 shale are low
the values consistently remain at a low level with no pronounced patterns of variation discernible
Longitudinal variation characteristics of the TOC content and major elements in the deep shale samples
The major element contents are significantly different in the WF, Long-11 and Long-12 shales (<a href="#F2">Figure 2</a>)
The SiO2 contents in the WF (59.01%&#x02013;75.45%
average of 68.84%) and Long-11 (58.15%&#x02013;76.65%
average of 65.20%) shales are higher than that of the Long-12 shale (56.45%&#x02013;58.19%
the Al2O3 and Fe2O3 contents of Long-12 are higher than those of in the WF and Long-11 shales
K2O and TiO2 contents in the WF and Long-11 shales are lower than those in the Long-12 shale
while the Na2O contents in the Long-11 shale are the highest
As shown in <a href="#F3">Figure 3</a>, compared with the long-12 shale, the Mo, U, V and Ni concentrations in the WF and Long-11 shales are more obviously enriched. Vertically, these elements increase first and then decrease from the bottom to the top. However, Cr, Co and P fluctuate but have no obvious trend (see <a href="#SM1">Supplementary Table S2</a>). Compared with the PAAS (<a href="#B76">Wedepohl, 1971</a>)
the Mo and U contents of these shales in the present study are relatively enriched
Long-11 and Long-12 shales are 4.96&#x02013;188.86 (average of 97.39)
8.70&#x02013;114.00 (average of 31.19) and 2.25&#x02013;11.16 (average of 7.12)
The UEF of these three shales are 2.11&#x02013;30.25 (average of 17.60)
Characteristics of longitudinal variations in trace elements in deep shale samples
PAAS normalized REE distribution model of the (A) Long-12
the CIA values decrease with decreasing burial depth
reflecting a gradually colder climate corresponding to a widespread global ice age
reflecting the change in paleoclimate toward warm and humid conditions
accompanied by an increase in weathering intensity
Longitudinal variation characteristics of geochemical indexes of deep shale samples
Fe2O3 and MnO are 1.77%&#x02013;6.41% (mean: 4.48%) and 0.02%&#x02013;0.10% (mean: 0.05%)
suggesting that these three shales are of normal marine non-hydrothermal origin
Figure 6. (A) Al2O3/TiO2 vs. (Al)/(Mn&#x0002b;Al&#x0002b;Fe) (<a href="#B16">Feng et al., 2023a</a>); (B) Al-Fe-Mn ternary diagram (<a href="#B1">Adachi et al., 1986</a>)
because changes in terrigenous detrital input may affect the concentration of OM in marine sediments
The relationships between TOC and Al (A) and Ti (B)
The lower sedimentation rate contributes to the OMA in the WF shale
an increase in the sedimentation rate helps to reduce the probability of OM being destroyed by oxidation during the sedimentation process
its sedimentation rate is obviously higher than that of the WF shale
Especially for the organic-rich shale of Long-11
the increase in sedimentation rate is synchronous with the decrease in TOC content
The redox conditions of the water column are one of the contributing factors to OMA, to which, an anoxic, oxygen-deficient environment is particularly conducive (<a href="#B6">Algeo and Maynard, 2004</a>). Redox-sensitive elements such as Mo, U, V, Cr, Co, Ni and Th have been widely used to assess the redox conditions of marine water bodies (<a href="#B5">Algeo and Lyons, 2006</a>)
Relationships between TOC and the redox indexes V/Cr (A) and Ni/Co (B) in the studied deep shale
Relationship between TOC and the redox index Corg/P in the studied deep shale
Figure 12. MoEF versus UEF in the studied deep shale samples (modified from <a href="#B8">Algeo and Tribovillard, 2009</a>)
This suggests that the productivity of the Long-11 shale positively influences its OMA
Relationships between TOC and Ni/Al (A) and P/Al (B) in the studied deep shale
intense volcanic activity resulted in the formation of an extremely anoxic environment and the deterioration of seawater properties
some organisms were unable to adapt and died over a wide area
with their remains rapidly deposited and buried before oxidative decomposition
Figure 14. Zr/Cr versus Zr/Al2O3 in the studied deep shale, Zr/Cr &#x0003d; 1.0 ppm/ppm, Zr/Al2O3 threshold &#x0003d; 6.0 ppm/wt% (threshold value cited <a href="#B83">Yang et al., 2022</a>)
The formation of organic-rich shales in marine environments is a complex process influenced by many factors. Globally, it is generally related to the activity cycle of ice age and plate movement (<a href="#B59">Shen et al., 2023</a>). At the basin level, factors such as primary productivity, redox conditions, terrigenous detrital input and sedimentation rate play significant roles in controlling OMA (<a href="#B13">Demaison and Moore, 1980</a>; <a href="#B79">Wu et al., 2021</a>)
The primary factors controlling OMA can vary distinctly across different stages
particularly during the complex geological events of the Late Ordovician and Early Silurian periods
it is necessary to clarify the mechanism of OMA by considering the interplay between the main controlling factors and geological events
By comparing the paleoclimate conditions during shale formation with the longitudinal variation trend of the TOC content (<a href="#F5">Figure 5</a>)
it is found that the chemical weathering index has no significant effect on the OMA
This can be attributed to the overall low to medium degree of chemical weathering during the sedimentation of the WF-Long-1 shales
indicating that individual climate factors had little influence on the OMA
These findings suggest that paleoclimate conditions are not the main controlling factor affecting the OMA
The slow deposition rate mitigated the adverse influence of terrigenous debris input on OMA to a certain extent
and finally resulted in the deposition of high-quality shale with a small thickness
Organic matter enrichment model of the WF-LMX formation in the Dingshan area
(A) WF shale; (B) Long-11 shale; (C) Long-12 shale
the upwelling brought nutrients to the surface
creating ideal conditions for the growth and proliferation of aquatic organisms
global sea level rise exceeds tectonic uplift
resulting in a low degree of basin limitation
in combination with the input of terrigenous clastic material and increased sedimentation rates
the TOC content of the Long-11 shale was found to be lower than that of the WF shale
the Long-11 shale remains a high-quality shale overall
During the sedimentary period of the Long-12 shale (<a href="#F15">Figure 15C</a>). In the absence of nutrients provided by upwelling, nutrient-poor seawater resulted in a low level of primary productivity. Meanwhile, the terrigenous debris input and sedimentation rate increased and diluted the OM flux due to the decrease in sea level (<a href="#F5">Figure 5</a>)
low productivity level and poor bottom water preservation conditions are the fundamental reasons for the formation of organic-poor shale
The depositional environments of the WF-LMX shale at well DY7 in the Dingshan area of the Sichuan Basin
and the mechanisms driving the OMA were explored
This work culminates in several pivotal conclusions:
a prevailing strongly reducing environment
coupled with frequent volcanic activities that supplied abundant nutrients
fostered conditions conducive to heightened productivity
Low terrigenous clastic input and sedimentation rates further promoted optimal preservation conditions
the WF shale is characterized by a notably high TOC
the organic-rich shale was positively influenced by a strong reducing environment and high paleoproductivity
while terrigenous clastic input and sedimentation rate somewhat restricted OMA
the TOC content of the Long-11 shale is lower than that of the WF shale
the oxic conditions of the water column prevented the effective preservation of OM
the increase in terrigenous clasts and sedimentation rates further diluted the OM
leading to low productivity levels and subsequently low OM contents
The original contributions presented in the study are included in the article/<a href="#SM1">Supplementary Material</a>
further inquiries can be directed to the corresponding author
The author(s) declare that financial support was received for the research
This study was financially supported by the National Natural Science Foundation of China (U19B6003-03-01; 42330811).The authors are grateful to the Sinopec Exploration Branch Company for providing core samples
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations
Any product that may be evaluated in this article
or claim that may be made by its manufacturer
is not guaranteed or endorsed by the publisher
The Supplementary Material for this article can be found online at: <a href="https://www.frontiersin.org/articles/10.3389/feart.2024.1457377/full#supplementary-material">https://www.frontiersin.org/articles/10.3389/feart.2024.1457377/full&#x00023;supplementary-material</a>
Hydrothermal chert and associated siliceous rocks from the northern Pacific their geological significance as indication od ocean ridge activity
<a href="https://doi.org/10.1016/0037-0738(86)90075-8">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Hydrothermal+chert+and+associated+siliceous+rocks+from+the+northern+Pacific+their+geological+significance+as+indication+od+ocean+ridge+activity&amp;btnG=">Google Scholar</a>
Volcanic triggering of a biogeochemical cascade during oceanic anoxic event 2
<a href="https://doi.org/10.1038/ngeo743">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Volcanic+triggering+of+a+biogeochemical+cascade+during+oceanic+anoxic+event+2&amp;btnG=">Google Scholar</a>
Redox classification and calibration of redox thresholds in sedimentary systems
<a href="https://doi.org/10.1016/j.gca.2020.01.055">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Redox+classification+and+calibration+of+redox+thresholds+in+sedimentary+systems&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1016/j.palaeo.2007.02.029">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Sedimentary+Corg:P+ratios,+paleocean+ventilation,+and+Phanerozoic+atmospheric+pO2&amp;btnG=">Google Scholar</a>
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Trace-element behavior and redox facies in core shales of Upper Pennsylvanian Kansas-type cyclothems
<a href="https://doi.org/10.1016/j.chemgeo.2003.12.009">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Trace-element+behavior+and+redox+facies+in+core+shales+of+Upper+Pennsylvanian+Kansas-type+cyclothems&amp;btnG=">Google Scholar</a>
Paleoceanographic applications of trace-metal concentration data
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<a href="https://doi.org/10.1016/0025-3227(93)90150-t">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geochemistry+of+Recent+oxic+and+anoxic+marine+sediments:+implications+for+the+geological+record&amp;btnG=">Google Scholar</a>
Factors influencing organic carbon preservation in marine sediments
<a href="https://pubmed.ncbi.nlm.nih.gov/11539298/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1016/0009-2541(94)90061-2">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Factors+influencing+organic+carbon+preservation+in+marine+sediments&amp;btnG=">Google Scholar</a>
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Facies patterns and geography of the Yangtze region
through the ordovician and silurian transition
<a href="https://doi.org/10.1016/s0031-0182(03)00736-3">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Facies+patterns+and+geography+of+the+Yangtze+region,+south+China,+through+the+ordovician+and+silurian+transition&amp;btnG=">Google Scholar</a>
Anoxic environments and oil source bed genesis
<a href="https://doi.org/10.1016/0146-6380(80)90017-0">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Anoxic+environments+and+oil+source+bed+genesis&amp;btnG=">Google Scholar</a>
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<a href="https://doi.org/10.1016/j.marpetgeo.2024.106805">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Water+distribution+in+pore+systems+and+its+influences+on+gas-bearing+property+of+deep+shale:+a+case+study+of+the+Longmaxi+Formation+in+the+Luzhou+area,+southern+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Restoration of sedimentary environment and geochemical features of deep marine Longmaxi shale and its significance for shale gas: a case study of the Dingshan area in the Sichuan Basin
<a href="https://doi.org/10.1016/j.marpetgeo.2023.106186">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Restoration+of+sedimentary+environment+and+geochemical+features+of+deep+marine+Longmaxi+shale+and+its+significance+for+shale+gas:+a+case+study+of+the+Dingshan+area+in+the+Sichuan+Basin,+South+China&amp;btnG=">Google Scholar</a>
Gas storage in shale pore system: a review of the mechanism
<a href="https://doi.org/10.1016/j.petsci.2023.05.012">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Gas+storage+in+shale+pore+system:+a+review+of+the+mechanism,+control+and+assessment&amp;btnG=">Google Scholar</a>
Oil retention in shales: a review of the mechanism
<a href="https://doi.org/10.3389/feart.2021.720839">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Oil+retention+in+shales:+a+review+of+the+mechanism,+controls+and+assessment&amp;btnG=">Google Scholar</a>
Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic: suboxic diagenesis
<a href="https://doi.org/10.1016/0016-7037(79)90095-4">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Early+oxidation+of+organic+matter+in+pelagic+sediments+of+the+eastern+equatorial+Atlantic:+suboxic+diagenesis&amp;btnG=">Google Scholar</a>
Gas in place and its controlling factors of deep shale of the Wufeng-Longmaxi Formations in the Dingshan area
<a href="https://doi.org/10.1007/s11707-021-0966-5">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Gas+in+place+and+its+controlling+factors+of+deep+shale+of+the+Wufeng-Longmaxi+Formations+in+the+Dingshan+area,+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Effect of silica diagenesis on porosity evolution of deep gas shale reservoir of the Lower Paleozoic Wufeng-Longmaxi formations
<a href="https://doi.org/10.1016/j.marpetgeo.2022.105873">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Effect+of+silica+diagenesis+on+porosity+evolution+of+deep+gas+shale+reservoir+of+the+Lower+Paleozoic+Wufeng-Longmaxi+formations,+Sichuan+Basin&amp;btnG=">Google Scholar</a>
The &#x0201c;North American shale composite&#x0201d;; its compilation
<a href="https://doi.org/10.1016/0016-7037(84)90298-9">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+North+American+shale+composite;+its+compilation,+major+and+trace+element+characteristics&amp;btnG=">Google Scholar</a>
Deep and ultra-deep natural gas exploration in the Sichuan Basin: progress and prospect
<a href="https://doi.org/10.1016/j.ngib.2020.05.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Deep+and+ultra-deep+natural+gas+exploration+in+the+Sichuan+Basin:+progress+and+prospect&amp;btnG=">Google Scholar</a>
The distribution and substitution mechanism of trace elements in cassiterites: constraints from LA-ICP-MS U-Pb dating
elemental mapping and in situ trace element analyses of the Gejiu tin polymetallic deposit
<a href="https://doi.org/10.1016/j.chemgeo.2022.121063">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+distribution+and+substitution+mechanism+of+trace+elements+in+cassiterites:+constraints+from+LA-ICP-MS+U-Pb+dating,+elemental+mapping+and+in+situ+trace+element+analyses+of+the+Gejiu+tin+polymetallic+deposit,+SW+China&amp;btnG=">Google Scholar</a>
Challenges and countermeasures of effective development with large scale of deep shale gas in Sichuan Basin
doi:10.13809/j.cnki.cn32-1825/te.2021.02.001
<a href="https://doi.org/10.13809/j.cnki.cn32-1825/te.2021.02.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Challenges+and+countermeasures+of+effective+development+with+large+scale+of+deep+shale+gas+in+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Identification and evaluation of shale oil micro-migration and its petroleum geological significance
<a href="https://doi.org/10.1016/s1876-3804(24)60010-8">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Identification+and+evaluation+of+shale+oil+micro-migration+and+its+petroleum+geological+significance&amp;btnG=">Google Scholar</a>
Characteristics of paleo oil pools from Sinian to Lower Paleozoic in southeastern margin of Sichuan basin
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characteristics+of+paleo+oil+pools+from+Sinian+to+Lower+Paleozoic+in+southeastern+margin+of+Sichuan+basin&amp;btnG=">Google Scholar</a>
Controls on organic matter accumulation on the early-Cambrian western Yangtze Platform
<a href="https://doi.org/10.1016/j.marpetgeo.2019.08.005">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Controls+on+organic+matter+accumulation+on+the+early-Cambrian+western+Yangtze+Platform,+South+China&amp;btnG=">Google Scholar</a>
Sea-level changes control organic matter accumulation in the Longmaxi shales of southeastern Chongqing
<a href="https://doi.org/10.1016/j.marpetgeo.2020.104478">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Sea-level+changes+control+organic+matter+accumulation+in+the+Longmaxi+shales+of+southeastern+Chongqing,+China&amp;btnG=">Google Scholar</a>
Comparison of geochemical indices used for the interpretation of palaeoredox conditions in ancient mudstones
<a href="https://doi.org/10.1016/0009-2541(94)90085-x">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Comparison+of+geochemical+indices+used+for+the+interpretation+of+palaeoredox+conditions+in+ancient+mudstones&amp;btnG=">Google Scholar</a>
Biogenic silica and organic carbon fluxes provide evidence of enhanced marine productivity in the Upper Ordovician-Lower Silurian of South China
<a href="https://doi.org/10.1016/j.palaeo.2019.109278">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Biogenic+silica+and+organic+carbon+fluxes+provide+evidence+of+enhanced+marine+productivity+in+the+Upper+Ordovician-Lower+Silurian+of+South+China&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1029/jz071i024p06091">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Rare+earths+in+sediments&amp;btnG=">Google Scholar</a>
Mineralogy and inorganic geochemistry of the Es4 shales of the damintun sag
northeast of the bohai bay basin: implication for depositional environment
<a href="https://doi.org/10.1016/j.marpetgeo.2019.09.002">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mineralogy+and+inorganic+geochemistry+of+the+Es4+shales+of+the+damintun+sag,+northeast+of+the+bohai+bay+basin:+implication+for+depositional+environment&amp;btnG=">Google Scholar</a>
Depositional environment and organic matter accumulation of upper ordovician-lower silurian marine shale in the upper Yangtze Platform
<a href="https://doi.org/10.1016/j.palaeo.2016.11.037">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Depositional+environment+and+organic+matter+accumulation+of+upper+ordovician-lower+silurian+marine+shale+in+the+upper+Yangtze+Platform,+south+China&amp;btnG=">Google Scholar</a>
Depositional environment of oil shale within the second member of permian lucaogou formation in the santanghu basin
<a href="https://doi.org/10.1016/j.coal.2017.03.011">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Depositional+environment+of+oil+shale+within+the+second+member+of+permian+lucaogou+formation+in+the+santanghu+basin,+northwest+China&amp;btnG=">Google Scholar</a>
Reservoir space and enrichment model of shale oil in the first member of Cretaceous Qingshankou Formation in the Changling Sag
<a href="https://doi.org/10.1016/s1876-3804(21)60049-6">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Reservoir+space+and+enrichment+model+of+shale+oil+in+the+first+member+of+Cretaceous+Qingshankou+Formation+in+the+Changling+Sag,+southern+Songliao+Basin,+NE+China&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1016/j.earscirev.2020.103470">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Tectonic+evolution+of+the+Sichuan+Basin,+southwest+China&amp;btnG=">Google Scholar</a>
Geochemical constraints and astronomical forcing on organic matter accumulation of marine-continental transitional shale deposits in the qinshui basin during the carboniferous-permian transition
<a href="https://doi.org/10.1021/acsearthspacechem.3c00372">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geochemical+constraints+and+astronomical+forcing+on+organic+matter+accumulation+of+marine-continental+transitional+shale+deposits+in+the+qinshui+basin+during+the+carboniferous-permian+transition&amp;btnG=">Google Scholar</a>
Nanopore structure characteristics and evolution of type III kerogen in marine-continental transitional shales from the Qinshui basin
<a href="https://doi.org/10.1016/j.geoen.2022.211413">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Nanopore+structure+characteristics+and+evolution+of+type+III+kerogen+in+marine-continental+transitional+shales+from+the+Qinshui+basin,+northern+China&amp;btnG=">Google Scholar</a>
Characteristics of shale gas enrichment in tectonically complex regions-A case study of the Wufeng-Longmaxi Formations of Lower Paleozoic in southeastern Sichuan Basin
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characteristics+of+shale+gas+enrichment+in+tectonically+complex+regions-A+case+study+of+the+Wufeng-Longmaxi+Formations+of+Lower+Paleozoic+in+southeastern+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Geochemistry of mesoproterozoic hongshuizhuang formation shales inNorthern North China:lmplications for provenance and source weathering
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geochemistry+of+mesoproterozoic+hongshuizhuang+formation+shales+inNorthern+North+China:lmplications+for+provenance+and+source+weathering&amp;btnG=">Google Scholar</a>
Deep shale gas in China: geological characteristics and development strategies
<a href="https://doi.org/10.1016/j.egyr.2021.03.043">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Deep+shale+gas+in+China:+geological+characteristics+and+development+strategies&amp;btnG=">Google Scholar</a>
Geological characteristics and high production control factors of shale gas reservoirs in Silurian Longmaxi Formation
<a href="https://doi.org/10.1016/s1876-3804(20)60105-7">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geological+characteristics+and+high+production+control+factors+of+shale+gas+reservoirs+in+Silurian+Longmaxi+Formation,+southern+Sichuan+Basin,+SW+China&amp;btnG=">Google Scholar</a>
Relationships between the trace element composition of sedimentary rocks and upper continental crust
<a href="https://doi.org/10.1029/2000gc000109">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Relationships+between+the+trace+element+composition+of+sedimentary+rocks+and+upper+continental+crust&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1130/spe284-p21">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geochemical+approaches+to+sedimentation,+provenance,+and+tectonics&amp;btnG=">Google Scholar</a>
Pore characteristics and gas preservation of the lower cambrian shale in a strongly deformed zone
<a href="https://doi.org/10.3390/en15082956">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+characteristics+and+gas+preservation+of+the+lower+cambrian+shale+in+a+strongly+deformed+zone,+northern+chongqing,+China&amp;btnG=">Google Scholar</a>
Occurrence and maturation transformation of organic and inorganic nitrogen in the Lower Cambrian shelf&#x02013;slope facies shale: Implications for overmature N2-rich shale reservoirs in Southern China
<a href="https://doi.org/10.1016/j.marpetgeo.2024.107011">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Occurrence+and+maturation+transformation+of+organic+and+inorganic+nitrogen+in+the+Lower+Cambrian+shelf–slope+facies+shale:+Implications+for+overmature+N2-rich+shale+reservoirs+in+Southern+China&amp;btnG=">Google Scholar</a>
Early Proterozoic climates and plate motions inferred from major element chemistry of lutites
<a href="https://doi.org/10.1038/299715a0">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Early+Proterozoic+climates+and+plate+motions+inferred+from+major+element+chemistry+of+lutites&amp;btnG=">Google Scholar</a>
Formation and diagenesis of weathering profiles
<a href="https://doi.org/10.1086/629290">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Formation+and+diagenesis+of+weathering+profiles&amp;btnG=">Google Scholar</a>
Petrogenesis of sediments in the absence of chemical weathering: effects of abrasion and sorting on bulk composition and mineralogy
<a href="https://doi.org/10.1046/j.1365-3091.1996.d01-12.x">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Petrogenesis+of+sediments+in+the+absence+of+chemical+weathering:+effects+of+abrasion+and+sorting+on+bulk+composition+and+mineralogy&amp;btnG=">Google Scholar</a>
Deep shale gas in the Ordovician-Silurian Wufeng-Longmaxi formations of the Sichuan Basin
SW China: insights from reservoir characteristics
preservation conditions and development strategies
<a href="https://doi.org/10.1016/j.jseaes.2022.105521">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Deep+shale+gas+in+the+Ordovician-Silurian+Wufeng-Longmaxi+formations+of+the+Sichuan+Basin,+SW+China:+insights+from+reservoir+characteristics,+preservation+conditions+and+development+strategies&amp;btnG=">Google Scholar</a>
Environmental response to volcanic activity and its effect on organic matter enrichment in the permian lucaogou formation of the malang sag
<a href="https://doi.org/10.1016/j.palaeo.2020.110024">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Environmental+response+to+volcanic+activity+and+its+effect+on+organic+matter+enrichment+in+the+permian+lucaogou+formation+of+the+malang+sag,+santanghu+basin,+northwest+China&amp;btnG=">Google Scholar</a>
Productivity what controls the formation of organic-carbon-rich sediments and sedimentary rocks
doi:10.1306/0c9b232b-1710-11d7-8645000102c1865d
<a href="https://doi.org/10.1306/0c9b232b-1710-11d7-8645000102c1865d">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Anoxia+vs.+Productivity+what+controls+the+formation+of+organic-carbon-rich+sediments+and+sedimentary+rocks&amp;btnG=">Google Scholar</a>
Variations of organic matter content and type within the sequence stratigraphic framework of the lacustrine deep-water Dongyuemiao formation
<a href="https://doi.org/10.1016/j.marpetgeo.2023.106104">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Variations+of+organic+matter+content+and+type+within+the+sequence+stratigraphic+framework+of+the+lacustrine+deep-water+Dongyuemiao+formation,+Sichuan+Basin,+Western+China&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1016/j.chemgeo.2003.12.006">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+modern+vs.+Permian+black+shale;+the+hydrography,+primary+productivity,+and+water-column+chemistry+of+deposition&amp;btnG=">Google Scholar</a>
Discussion of the relationship between volcanic ash layers and organic enrichment of black shale: a case study of the wufeng-longmaxi gas shales in the Sichuan Basin
<a href="https://doi.org/10.14027/j.issn.1000-0550.2019.088">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Discussion+of+the+relationship+between+volcanic+ash+layers+and+organic+enrichment+of+black+shale:+a+case+study+of+the+wufeng-longmaxi+gas+shales+in+the+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Relationship between degree of water retention and enrichment of shale organic matter during the Ordovician-Silurian transition in western Hubei
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Relationship+between+degree+of+water+retention+and+enrichment+of+shale+organic+matter+during+the+Ordovician-Silurian+transition+in+western+Hubei&amp;btnG=">Google Scholar</a>
Geological characteristics analysis and favorable area optimization of upper shale gas reservoir of Jiaoshiba block in Fuling Gas Field
<a href="https://doi.org/10.11781/sysydz202101034">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geological+characteristics+analysis+and+favorable+area+optimization+of+upper+shale+gas+reservoir+of+Jiaoshiba+block+in+Fuling+Gas+Field,+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Geological characteristics and development potential of upper shale gas reservoirs of No.1 member of Longmaxi Formation in Jiaoshiba area
<a href="https://doi.org/10.11764/j.issn.1672-1926.2019.12.016">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geological+characteristics+and+development+potential+of+upper+shale+gas+reservoirs+of+No.1+member+of+Longmaxi+Formation+in+Jiaoshiba+area,+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Phosphatases relieve carbon limitation of microbial activity in Baltic Sea sediments along a redox-gradient
<a href="https://doi.org/10.4319/lo.2011.56.6.2018">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Phosphatases+relieve+carbon+limitation+of+microbial+activity+in+Baltic+Sea+sediments+along+a+redox-gradient&amp;btnG=">Google Scholar</a>
Depositional environment and hydrothermal controls on organic matter enrichment in the lower Cambrian Niutitang shale
<a href="https://doi.org/10.1306/12222018196">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Depositional+environment+and+hydrothermal+controls+on+organic+matter+enrichment+in+the+lower+Cambrian+Niutitang+shale,+southern+China&amp;btnG=">Google Scholar</a>
The continental crust its composition and evolution
<a href="https://doi.org/10.1017/s0016756800032167">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+continental+crust+its+composition+and+evolution&amp;btnG=">Google Scholar</a>
Trace metals as paleoredox and paleoproductivity proxies: an update
<a href="https://doi.org/10.1016/j.chemgeo.2006.02.012">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Trace+metals+as+paleoredox+and+paleoproductivity+proxies:+an+update&amp;btnG=">Google Scholar</a>
Distribution of phosphorus in sediments from tomales bay
<a href="https://doi.org/10.1016/s0025-3227(96)00109-0">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Distribution+of+phosphorus+in+sediments+from+tomales+bay,+California&amp;btnG=">Google Scholar</a>
A kinetic study of aluminum adsorption by aluminosilicate clay minerals
<a href="https://doi.org/10.1016/0016-7037(88)90056-7">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+kinetic+study+of+aluminum+adsorption+by+aluminosilicate+clay+minerals&amp;btnG=">Google Scholar</a>
Oil content and resource quality evaluation methods for lacustrine shale: a review and a novel three-dimensional quality evaluation model
<a href="https://doi.org/10.1016/j.earscirev.2022.104134">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Oil+content+and+resource+quality+evaluation+methods+for+lacustrine+shale:+a+review+and+a+novel+three-dimensional+quality+evaluation+model&amp;btnG=">Google Scholar</a>
Sedimentary differentiation triggered by the Toarcian Oceanic Anoxic Event and formation of lacustrine shale oil reservoirs: organic matter accumulation and pore system evolution of the Early Jurassic sedimentary succession
<a href="https://doi.org/10.1016/j.jseaes.2023.105825">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Sedimentary+differentiation+triggered+by+the+Toarcian+Oceanic+Anoxic+Event+and+formation+of+lacustrine+shale+oil+reservoirs:+organic+matter+accumulation+and+pore+system+evolution+of+the+Early+Jurassic+sedimentary+succession,+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
Comprehensive characterization and evaluation of deep shales from Wufeng-Longmaxi Formation by LF-NMR technology
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New geochemical identification fingerprints of volcanism during the Ordovician-Silurian transition and its implications for biological and environmental evolution
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and organic matter accumulation of marine oil shale from the Changliang Mountain area
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Influence of the Late Ordovician-Early Silurian paleoenvironment and related geological processes on the organic matter accumulation and carbon isotope excursion
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oxygen and strontium isotopic and elemental characteristics of the Cambrian Longwangmiao Formation in South China: paleoenvironmental significance and implications for carbon isotope excursions
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Sedimentation models and development mechanisms of organic-rich shales of the lower carboniferous dawuba formation: a case study in the yaziluo rift trough
<a href="https://pubmed.ncbi.nlm.nih.gov/36033673/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/acsomega.2c02901">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Sedimentation+models+and+development+mechanisms+of+organic-rich+shales+of+the+lower+carboniferous+dawuba+formation:+a+case+study+in+the+yaziluo+rift+trough,+south+of+Guizhou+province,+southern+China&amp;btnG=">Google Scholar</a>
Factors controlling the heterogeneity of shale pore structure and shale gas production of the Wufeng&#x02013;Longmaxi shales in the Dingshan plunging anticline of the Sichuan Basin
<a href="https://doi.org/10.1016/j.coal.2023.104434">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Factors+controlling+the+heterogeneity+of+shale+pore+structure+and+shale+gas+production+of+the+Wufeng–Longmaxi+shales+in+the+Dingshan+plunging+anticline+of+the+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
potential and prospect of shale gas in China
<a href="https://doi.org/10.3787/j.issn.1000-0976.2021.01.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Development+progress,+potential+and+prospect+of+shale+gas+in+China&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1016/j.earscirev.2018.12.002">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Organic-matter-rich+shales+of+China&amp;btnG=">Google Scholar</a>
Tan Y and Xiao X (2024) Influence of the sedimentary environment of the Wufeng-Longmaxi shale on organic matter accumulation in the Dingshan area
Received: 30 June 2024; Accepted: 23 July 2024;Published: 06 August 2024
Copyright &#x000a9; 2024 Wang, Feng, Gao, Meng, Lu, Fan, Li, Tan and Xiao. This is an open-access article distributed under the terms of the <a rel="license" href="http://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution License (CC BY).</a> The use
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&#x0002a;Correspondence: Yue Feng, <a id="encmail">ZmVuZ3kwOTkxQDE2My5jb20=</a>
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When 17-year-old Lin Shih (林石) crossed the Taiwan Strait in 1746 with a group of settlers, he could hardly have known the magnitude of wealth and influence his family would later amass on the island, or that one day tourists would be walking through the home of his descendants in central Taiwan.
He might also have been surprised to see the family home located in Wufeng District (霧峰) of Taichung, as Lin initially settled further north in what is now Dali District (大里).
However, after the Qing executed him for his alleged participation in the Lin Shuang-Wen Rebellion (林爽文事件), his grandsons were taken south by their mother for a fresh start. Future generations of the Lin family did not rebel against the Qing, and were actually staunch supporters whose military exploits helped cement their fame and fortune.
In the next (fourth) generation of the Lin family, the Wufeng property was split into an Upper House and a Lower House, perhaps simplifying family financial matters at the time but greatly complicating tourist visits today. On top of this, the Upper House has now been further divided into four sites managed by two different entities, with some requiring advance reservations. The Lower House property, however, is accessible in its entirety with one ticket and is the focus of this article.
On the north side of the Lower House grounds is the oldest extant home belonging to the Wufeng Lin family, the Caocuo (草厝), or “grass house”, so named due to its thatched roof. Damaged in the 1935 earthquake, it was finally meticulously restored and reopened to the public just five years ago. Originally built around 1837, this simple brick structure symbolizes the family’s humble beginnings, and stands in stark contrast to the adjacent multi-layered mansion.
After passing through the main entrance and an indoor space, there is a courtyard and another entrance, followed by another courtyard and another entrance, followed by even more. When Lin Wen-cha’s son had expanded the home to its present size by 1895, it had a total of five “layers” (indoor spaces running left to right across the property) with four courtyards in between, making it one of the largest private residences in Taiwan.
The home is richly decorated with symbols for longevity and wealth that a guided tour will reveal. The pamphlet given out at the ticket counter also has a QR code linking to guided tour videos in passable English, which introduce some of these symbols.
When important visitors came to call on the Lins, their sedan chairs could be carried all the way through into the second layer, which was large enough to hold the chair during the guest’s visit. Guests were greeted by the head of the Lin household here, and escorted through the next courtyard into the third layer.
When such a guest was a suitor seeking the hand of a Lin girl in marriage, the girl could peek at the man through special windows on the side called “son-in-law windows.” This was the only chance the girl had to evaluate a suitor before the wedding.
The courtyard beyond the third layer seems especially large. This is because the fourth layer of the house was damaged in the infamous 1935 earthquake, so only the foundation remains today. Reconstruction of historical buildings must be based on visual records, but none exist for this part of the house, so reconstruction has not been possible.
The final layer of Gong-Bao-Di has never been open to the public. Initially, it was where the unmarried Lin females were housed. Nowadays, it serves as the ancestral hall for the Wufeng Lins. The exterior, however, is worth admiring on its own, especially the intricate woodwork covering the windows in alternating blue and green patches.
If Gong-Bao-Di is representative of the Lin family’s military success, the Grand Flower Hall just to the south symbolizes their admiration for literature and the arts. It was erected by Lin Chao-tung (林朝棟), of the sixth generation, in the 1890s, at a time when the Lin family enjoyed exclusive rights for camphor exports from Taiwan and was at the peak of their wealth and influence.
The showpiece of this hall is the theatrical stage in the middle courtyard, now the only Fuzhou-style wooden stage in Taiwan. The best seat in the house for watching performances was directly across from the stage, in the formal living room area, where two chairs — one for the head of the household and one for the night’s most distinguished guest — sit in an alcove surrounded by exquisite wooden carvings.
Facing the stage from here during a daytime tour, what stands out immediately is the symmetry of the stage and the ornamental carved window at the back that fully fills the space between the two entrance curtains. In fact, very little of the entire structure is undecorated.
It’s unfortunate that the building is usually only open for tours during the day, because this stage would look even more impressive at night, with its sharply-angled swallow-tail roof lit up from below as it reaches upward into the black expanse of the heavens. For an idea of how this would look, check out the music video for Jolin Tsai’s (蔡依林) song I’m Not Yours, which was filmed right here, or sign up for the exclusive night tour coming up on Feb. 8.
The stage itself is not open to the public, but visitors may observe it up close from ground level. The stage’s ceiling features a massive hanging wooden peony — a favorite decoration throughout the Lin family’s residence — in a multi-level recessed octagonal space. Underneath the stage are several earthenware jars. These would have been filled with water during performances to serve as resonators, naturally amplifying sounds from the stage.
This is the full extent of the Wufeng Lin family’s Lower House that is open to the public. If you have time, you may also want to check out the Upper House properties, including the Yipu Mansion next door or the Lin garden at the nearby Mingtai High School, neither of which require advance reservations.
Toward the outside edge of Taichung City, in Wufeng District (霧峰去), sits a sprawling collection of single-story buildings with tiled roofs belonging to the Wufeng Lin (霧峰林家) family, who rose to prominence through success in military, commercial, and artistic endeavors in the 19th century.
Most of these buildings have brick walls and tiled roofs in the traditional reddish-brown color, but in the middle is one incongruous property with bright white walls and a black tiled roof: Yipu Garden (頤圃).
Purists may scoff at the Japanese-style exterior and its radical departure from the Fujianese architectural style of the surrounding buildings. However, the property has great value as a historical snapshot of the reality facing Taiwanese during the Japanese era: modernize, or be left behind.
By the time construction was completed in 1914, the Qing empire had collapsed and Japanese rule had been entrenched in Taiwan for nearly two decades. Yipu Garden’s designer, Lin Ji-tang (林紀堂) was looking to the future. This does not mean his house was made to look entirely Japanese, however. There are elements of Chinese and Western influence — not to mention a secret escape tunnel — making the eclectic Yipu Garden a fascinating place to visit.
To enter Yipu Garden, visitors pass by a curving wall and through a gate facing one wing of the house, not the central hall. This was meant to represent a meandering river flowing into the property and its water being captured by one long arm of the building, with the water in turn symbolizing money. Back when the Lin family were major landlords, farmers would enter here and pay their rent in cash or grain in this extended arm of the house.
The property is rich with such symbolism and adherence to principles of fengshui, which the English signs do a decent job of explaining even without a guided tour. The wing of the house one faces when entering is represented by the tiger, which allegedly despises loud noise but doesn’t mind strong smells, so the kitchen and bathrooms can be found on this side.
The old accounting office in this wing has been transformed into a quaint restaurant, Yipu Vegan. Take a minute of your time to peek into the adjacent bathrooms — the toilets are white with blue painted decoration in the style of Ming Dynasty porcelain, and quite attractive, at least as far as toilets go.
Proceed through another gate into the inner courtyard to start your tour of the house’s interior. The house is a three-sided structure much like other Fujian-style houses in Taiwan, but the resemblance stops there. The covered walkways alongside the wings have narrow pillars topped with curved braces, reminiscent of the platforms in several Japanese-era train stations in Taiwan. The interior of the house also displays a high degree of foreign influence.
Proceeding into the tiger wing on the left, you will see a kitchen and casual dining area that look remarkably Western, with wooden cabinets, attractive shelving to display dishware, and an open view over the countertop between the two spaces. The painted floral tile table puts the final touch on a space that feels more like the south of France than Taichung.
The formal dining room contains a round table with lazy Susan as is commonly seen in Taiwanese restaurants. The painting hanging above the table, though painted by a local, is distinctly Western in style, as the artist studied in Europe. The sliding doors connecting the remaining spaces also feature quintessentially Western elements: stained glass windows.
The Lins did their best to adapt to life under the Japanese, and then the Chinese Nationalist Party (KMT) after World War II, but the design of the bedroom still reveals a keen awareness that life might not always be stable and predictable for this prominent family. The cabinets in the wall next to the bed are actually doors in disguise. Behind these doors is a secret room, in which a trapdoor leads to an underground bunker and escape tunnel.
The secret room is also covered in mirrors designed to distract enemies and make them feel more vulnerable. Sniper holes in the wall on the second floor, if manned, would make it nearly impossible for any intruder to survive long enough in the room to locate the escape hatch. The secret tunnel is open to visitors now, but must be accessed from the tunnel’s outdoor exit at the back of the house.
During the Japanese era, an exotic animal zoo was located behind the central wing of Yipu Garden and was a common destination for Japanese tourists. Nowadays, the zoo is long gone and the building that was located here, severely damaged in the massive 921 Earthquake, has been cleared away.
The tour thus continues in the dragon wing, opposite the tiger wing. Dragons apparently don’t mind loud noise, so it was here that games and musical performances took place.
A special room just for women is located at the back of this wing. The floor was decorated with playing card suits, indicating that the main purpose of the room was for games. The slender wooden chairs here were specifically designed with women in mind, and the ebony mahjong table had drawers without handles that could only be easily opened by someone with long fingernails. The Gothic style bay window once again adds a Western touch to the space.
The designer’s son, Lin Ho-nen (林鶴年), studied music and theater in Japan, where he met his second wife, a Japanese woman. In order to make her feel more comfortable in Taiwan, he built a tatami room for her in the dragon wing. The two also performed together in the adjacent concert room, he on the piano and she — trained in opera in Europe — singing soprano.
The couple never had any children, and the property now belongs to one of Lin Ho-nen’s second cousin’s descendants, Lin Chen-ting (林振廷). His son, Hanss Lin (林帛亨), is a professional race car driver and one room is now dedicated to displaying his achievements and memorabilia.
Concluding the tour is another somewhat related item sitting outdoors under a canopy: not a race car, but a Toyota Crown Royal Saloon sedan formerly owned by the Saudi ambassador to the Republic of China. After the countries severed diplomatic relations, the Lin family purchased the car and have maintained it in working order up to the present.
>> The English signage is adequate enough for a self-guided visit, but guided tours (Chinese only) can also be arranged every day through the Web site: wufeng-yipu.com.tw/reservation. One advantage of the guided tour is that the guide will also take you across the street to the family’s art warehouse, where you can have a quick look at their extensive collection of artwork and Qing-era artifacts, and get an excellent view of all the Lin family’s historical buildings from the upper-floor balcony.
>> Regular admission to Yipu Garden costs NT$150, or NT$250 for admission with a guided tour. The park is open 10am to 5pm from Tuesday to Sunday.
Volume 12 - 2024 | <a class="ArticleLayoutHeader__info__doi" href="https://doi.org/10.3389/feart.2024.1375241">https://doi.org/10.3389/feart.2024.1375241</a>
In the deep Longmaxi Formation shale gas reservoirs of the southern Sichuan Basin
strong overpressure is universally developed to varying degrees
there is currently a lack of in-depth research on the formation mechanisms
and the controlling effects on reservoir pore characteristics of strong overpressure
This limitation significantly restricts the evaluation of deep shale gas reservoirs
This study selected typical overpressured shale gas wells in Yongchuan
Through comprehensive methods such as log analysis
the dominant mechanisms of strong overpressure formation were determined
and the pressure evolution from early burial to late strong uplift was characterized
the impact of varying degrees of overpressure on reservoir pore characteristics was studied using techniques such as scanning electron microscopy
The research findings indicate that hydrocarbon generation expansion is the primary mechanism for strong overpressure formation
The pressure evolution in the early burial phase is controlled by the processes of kerogen oil generation and residual oil cracking into gas
The reservoir experienced three stages: normal pressure (Ordovician to Early Triassic)
overpressure (Early Triassic to Early Jurassic)
and strong overpressure (Early Jurassic to Late Cretaceous)
with pressure coefficients of approximately 1.08
the adjustment of early overpressure occurred due to temperature decrease and gas escape
leading to a decrease in formation pressure from 140.55 MPa to 81.63 MPa
while still maintaining a state of strong overpressure
Different degrees of strong overpressure exert a significant control on the physical properties of shale reservoirs and the composition of organic matter pores
Variations exist in the organic matter pore morphology
and connectivity within the deep Wufeng-Longmaxi shale
Higher overpressure favors the preservation of organic large pores and reservoir porosity
Under conditions of strong overpressure development
deep siliceous shales and organically rich clay shales exhibit favorable reservoir properties
By determining the dominant mechanisms of strong overpressure in the Wufeng-Longmaxi Formation and studying pore characteristics
this research not only deepens the understanding of the geological features of deep shale gas reservoirs but also provides a new perspective for understanding the overpressure mechanisms and reservoir properties of deep shale gas reservoirs
it is of significant importance for guiding the exploration and development of deep Longmaxi shale and provides valuable references for further research in related fields
significant variations exist in shale porosity
and gas production among different deep areas
As the geological-geophysical response characteristics are understood
it is revealed that tectonic compression and pressure transmission are the causes of overpressure
It has been discovered that the overpressure in many basins or areas may be the result of multiple causes
a detailed characterization of the impact of overpressure (different overpressure coefficients) on pore development characteristics is still lacking
this study focused on three overpressured shale gas wells in southern Sichuan with pressure coefficients of 1.86 (Well Z202 in Dazu area)
The study firstly conducted theoretical analyses and applied various geophysical logging methods to identify the dominant mechanisms of overpressure formation
it constructed geological models of typical wells by virtue of the basin modeling software
and restored the paleopressure by systematically analyzing fluid inclusion
it employed a mathematical model to quantitatively characterize the entire process of pressure evolution
the study explored the reasons for the differential overpressure evolution
a comparative analysis of porosity and pore structure characteristics of reservoirs with different pressure coefficients was conducted to clarify the impact of overpressure on reservoir pore features
The Yongchuan area is located in the gently folded zone of southeastern Sichuan
characterized by a &#x0201c;two depressions with one uplift between them&#x0201d; structural pattern
The Wufeng Formation-Longmaxi Formation is widely distributed here
with a sedimentary thickness of approximately 360&#x02013;470 m
The overall variation in strata thickness is small
with burial depth gradually decreasing from northwest to southeast
but focused more on pressure evolution differences within three studied wells
and also its influence on reservoir pore characteristics
Figure 1. Planar distribution map of pressure coefficients in the Wufeng-Longmaxi formation shale gas reservoirs in the Southern and Southeastern Sichuan basin [adapted from <a href="#B42">Tang et al. (2022)</a>
Microscope equipped with transmission white light and incident ultraviolet light was used to observe fluid inclusions&#x02019; type and morphology in calcite veins. When the gas-liquid two-phase brine inclusions are artificially heated to a specific temperature, the multiphase state of the inclusions reverts to the initial single-phase fluid state, this specific temperature is homogenization temperature of the inclusion (<a href="#B34">Nie et al., 2020</a>)
By establishing a correlation curve between the Raman shift of methane gas and the pressure inside the inclusion
and based on the principle of maintaining constant total volume and composition of the inclusion
an iterative calculation model can be constructed to accurately calculate the capture pressure of the inclusion
The microthermometry measurements of thickly-polished sections were conducted using TH-600 Linkam heating platform
enabling determination of homogeneity temperature (Th) for gas-liquid two-phase brine inclusions with a reproducibility precision within &#x000b1;0.1
Raman spectroscopic measurements were performed using JY/Horiba LABRAM HR800 raman spectroscopy equipped with a 532 nm green laser and output power ranging from 200 to 500 mW
The ultra-high image resolution of focused ion beam-field emission scanning electron microscopy (FIB-SEM) enables effective observation of shale pore types and shapes
the shale sample is prepared into 1 cm2 before further SEM analysis
To enhance surface conductivity and obtain superior image quality
a Sputter Coater argon ion grinding instrument is utilized to uniformly plate the sample surface with gold
the Quanta250FEG is employed for controlled temperature (24 &#x000b0;C) and humidity level (35%) scanning of shale samples
MPa; &#x003c3; is the air-mercury interfacial tension
480 mN/m; &#x003b8; is air-mercury contact angle
Helium porosity measurements were carried out with Ultrapore-300 using helium expansion
The shale was made into cylindrical samples with a growth degree of 2.5 cm and a diameter of 2.5 cm
the sample was placed in a vacuum drying oven at 105 &#x000b0;C overnight
The volumetric density of the shale samples was measured by a caliper
while bone density calculations were performed based on multiple helium expansions conducted on dry samples
the porosity of the shale was determined by assessing the disparity between its volumetric density and skeletal density
an increasing number of scholars believe that overpressure resulting from disequilibrium compaction occurs in mechanically compacted environments at shallow burial depths with low geothermal gradients (less than 70 &#x000b0;C)
the formation of the overpressure in deeper burial environments is primarily attributed to hydrocarbon generation expansion
suggested that if the inversions of sonic velocity
Meanwhile it reflects possible causes such as fluid expansion
for overpressure caused by fluid expansion
the inversion of sonic velocity and resistivity is more significant than that of density
Overpressure distribution and causes identified from logging responses in the deep Longmaxi formation Shale of well H202 (A)
and Z202 (C) in the southern Sichuan basin
Figure 3. Overpressure distribution and causes identified from logging responses in the Longmaxi formation shale of well YS108, Zhaotong area, Southern Sichuan basin [modified from <a href="#B3">Chen et al. (2016)</a>; <a href="#B37">Rui et al. (2021)</a>]
The overpressure data points in typical crossplot fall on or to the right of the loading curve
due to the slight reduction in density influenced by organic matter enrichment
the overpressure data points in the study area shift slightly to the left
there could exist some controversy in using the sonic velocity vs
density crossplot to determine the dominant cause of overpressure
Figure 4. Typical plot for identifying shale overpressure using density vs. Sonic velocity crossplot (<a href="#B68">Zhao et al., 2017</a>) (A)
Sonic velocity in the deep Longmaxi formation shale of Southern Sichuan Basin (B&#x02013;D)
for the shale of the Wufeng Formation to the Longmaxi Formation in the Sichuan Basin
is identified as the most important mechanism for overpressure during the shale burial stage
the formation water content in organic pores is low in the Silurian shale gas reservoir
and the effect of formation water contraction due to temperature decrease on the reservoir space can be ignored
the changes in fluid pressure and pressure coefficients during the uplift process depend on the overall effects of pore rebound
This method first constructs a geological model (burial history-thermal history) using basin simulation software
then uses the corresponding mathematical model to quantitatively calculate the contributions of various factors after determining the dominated controlling factors of pressure evolution
and finally achieves a quantitative characterization of the entire pressure evolution process under the constraints of paleo-pressure recovery values and current pressure measurements
it can provide relatively accurate results and visually display pressure characteristics at different historical periods
this study will apply this new method to recover the pressure evolution history of the deep Longmaxi Formation shale in the southern Sichuan in the entire process of sedimentary subsidence to structural uplift
laying the foundation for the recovery of the pressure evolution history
The simulation results show that the evolution of the target layer can be divided into two stages
1) A long-term subsidence stage (444&#x02013;65 Ma)
during which the shale underwent two rapid subsidence events
the maximum burial depth of the shale reached 6,700 m
The formation temperature increased from 25&#x000b0;C to 210&#x000b0;C
and the organic matter maturity increased from 0.2% to 2.7%
during which the shale continued to experience strong uplift
with the current burial depth being approximately 4,100 m
The formation temperature decreased from 210&#x000b0;C to 129&#x000b0;C
while the organic matter maturity remained stable
the evolution curve of maturity over time obtained through simulation matched well with the measured equivalent vitrinite reflectance
validating the reliability of the geological model
and geological model calibration results of Well H202 in Yongchuan area
The final reservoir pressure reached 140.55 MPa with pressure coefficient being 2.09
Calculation results of pressure and pressure coefficient for the Longmaxi Formation shale gas reservoir in Well H202
the cumulative pressure increase in the shale due to oil generation was approximately 17.66 MPa
and the pore fluid pressure reached about 49.05 MPa
corresponding to a pressure coefficient of about 1.56; 3) Super-strong overpressure stage (Early Jurassic to Late Cretaceous
195&#x02013;65 Ma): The shale experienced substantial subsidence during this period
with organic matter maturity increasing from 1.30% to 2.70%
The crude oil retained in the shale cracked to generate a large amount of natural gas
significantly increasing fluid pressure and forming strong overpressure
the cumulative pressure increase in the shale due to oil generation was approximately 55.73 MPa
and the pore fluid pressure reached about 140.55 MPa
corresponding to a pressure coefficient of about 2.09
discretely dispersed single-phase methane inclusions exhibit characteristics of low transparency
with bright centers surrounded by a darker rim
primarily in the form of quadrilaterals and sub-rounded shapes
Gas-liquid two-phase brine inclusions are observed as colorless
transparent entities with small gas bubbles
commonly coexisting with methane inclusions
Characteristics of fibrous calcite veins in the Longmaxi formation shale of well H202 in the Yongchuan area (A)
Petrographic features of methane and brine inclusions within the veins (B)
Laser Raman spectrum of methane inclusions (C)
Homogenization temperatures of gas-liquid two-phase brine inclusions
N represents the number of inclusions analyzed (D)
Analysis results of vein and inclusions of well L202 in the Luzhou area (E&#x02013;H) and well Z202 in the Dazu area (I&#x02013;L)
the density value of methane inclusions is calculated to be 0.261 g/cm3
so it is classified as a supercritical high-density methane inclusion
It provides favorable conditions for the accurate calculation of capture pressures
Those main maximum temperature data in L202 shows a unimodal distribution from 160&#x000b0;C to 180&#x000b0;C
When the inclusions are heated and quenched in the HDAC with a suitable external pressure
it can be found that the inclusions return to their pre-heating form
Figure 7. Comparison of temperature measurement results of inclusions (FI) in traditional heating stage (A,B) and HDPC (C&#x02013;G) [adopted from <a href="#B48">Wang et al. 2022b</a>]
and cannot be restored to their initial state during uplift
resulting in a hysteresis rebound phenomenon
it is imperative to consider this factor in calculations
the subsequent equation was employed for computation
&#x003d1; represents rock&#x02019;s Poisson ratio (0.25); Cr and C&#x02009;w represent the coefficient of compressibility of rock and water; &#x003c1;r represents the average density of the denudated formation (2.65&#x000d7;103 kg/m3); g represents the acceleration of gravity (9.8 m/s2); &#x02206;h indicates the denudation thickness of the formation(m)
However, <a href="#B22">Li et al. (2016)</a> and <a href="#B11">Gao et al. (2019)</a> proposed that Longmaxi Formation shale predominantly develops micro- and nano-scale pores
and the rebound degree does not significantly change with increasing denudation thickness
Hence its impact on pressure evolution is negligible
In the uplift stage of Longmaxi Formation shale
a temperature decrease of approximately 80 &#x000b0;C inevitably led to changes in formation pressure
We employed two methods for pressure evolution during tectonic uplift
The first commonly used Soave-Redlich-Kwong (SRK) state equation is employed to quantitatively calculate the influence of temperature changes on fluid pressure in the gas reservoir during the uplift process
P represents pressure (MPa); T is temperature (K); V is molar volume of the gas (cm3/mol); R is the gas constant (8.314 J/mol/K); a(T) denotes inter-molecular attraction; b is the volume of gas molecules; &#x003c9; is the acentric factor of the gas; Tc and Pc are the critical temperature and pressure of the gas (190 K
4.599 MPa); Tr is the relative temperature of the gas
the ratio of the actual absolute temperature to its critical temperature
The second method is the equation of state (EOS) for supercritical CH4 system by <a href="#B7">Duan et al. (1992)</a>. The main factors affecting pressure changes in shales are temperatures and gas escape, which has a linear relationship with gas density. The gas volume or gas density can be evaluated by the equation of state for supercritical CH4 system (<a href="#B7">Duan et al., 1992</a>)
Empirical parameters &#x003b1;1&#x02212;&#x003b1;12, &#x003b1;,&#x003b2;,&#x003b3;,Tc,and&#x02009;Pc in EOS for CH4 are compiled by <a href="#B7">Duan et al. (1992)</a>
Tc is the critical temperature above which a gas cannot be liquefied by an increase of pressure
Pc is the pressure at given temperature to liquefy a gas
Tr and Pr can be calculated at given temperature and pressure condition in a specific basin
Evolutionary models of pressure and pressure coefficient in the deep Longmaxi formation shale gas reservoirs in the Yongchuan Area (A,D)
Pressure evolution histories of the deep Longmaxi Formation shale were individually established for Well L202 in Luzhou area, and Well Z202 in Dazu area (<a href="#F8">Figures 8B,C,E,F</a>)
A comparative analysis reveals similarities in pressure evolution during the sedimentation&#x02013;subsidence stage
Both shales exhibit intense overpressure due to hydrocarbon generation
reaching a formation pressure of approximately 140 MPa and a pressure coefficient of about 2.10 at the maximum burial depth of approximately 6,700 m
differences emerged during the uplift&#x02013;denudation process
The Luzhou area experienced the smallest decrease in formation pressure (pressure drop due to temperature decrease and gas escape are 24.50 MPa and 21.63 MPa
the current formation pressure and pressure coefficient are the highest
the Dazu area witnessed the largest decrease in formation pressure (pressure drop due to temperature decrease and gas escape are 29.33 MPa and 38.88 MPa
the current formation pressure and pressure coefficient are the lowest
This discrepancy reflects variations in gas reservoir preservation conditions
situated within the internal part of the gently inclined tectonic zone in southern Sichuan
is featured by limited large faults and primarily small faults
The extent of shale gas escape and the pressure drop are relatively low
resulting in current gas reservoir pressure coefficients generally ranging from 2.0 to 2.4
located at the boundary of the southern and central Sichuan tectonic zones
hosts several large faults trending northeast to southwest
This may contribute to relatively higher shale gas escape and pressure drop
resulting in overall pressure coefficients ranging from 1.8 to 2.0
Scanning electron microscope images of pore types in organic-rich Shale of the deep long 11 sub-member
including organic matter pores (A&#x02013;C)
intragranular dissolution pores (E&#x02013;G)
and diagenetic shrinkage fractures (H&#x02013;I)
An increase in pyrite content promotes the development of organic matter pores
with the diameters of organic matter pores in the periphery ranging from 20 to 70 nm
They often appear as approximately elliptical and irregular shapes with some interconnected with each other
with increasing pressure coefficients (Dazu &#x0003c; Yongchuan &#x0003c; Luzhou)
there is no consistent pattern in the variation of total pore volume
This suggests that the influence of increased overpressure (1.86&#x02013;2.24) on shale pore volume and specific surface area is relatively limited
Pore structure characteristics of organic-rich shale in the deep long 11 sub-member (Z-1 to Z-3: samples from well Z202 in Dazu area
pressure coefficient 1.86; H-1 to H-7: samples from well H202 in Yongchuan area
pressure coefficient 2.04; L-1 to L-6: samples from well L202 in Luzhou Area
Where, S is pore cross-sectional area. C is pore cross-sectional perimeter Within the range of 0&#x02013;1.0, the values closer to 1.0 indicate a more circular pore shape, and the values closer to 0 suggest increasingly irregular pore shapes. The statistical results indicate that organic pores with a shape factor greater than 0.7 constitute over 65% of the total, while those with a shape factor lower than 0.4 account for less than 9% (<a href="#F12">Figure 12B</a>)
This implies that the organic pores in the target layer of the study area are predominantly circular or subcircular
with fewer irregular and extremely irregular flattened angular pores
Morphological characteristics of organic pores in organic-rich shale of the deep long 11 sub-member in Southern Sichuan (A&#x02013;D) Dazu area; (E&#x02013;H) Yongchuan area; (I&#x02013;L) Luzhou area
Comparative analysis of organic pore size range (A) and shape factor (B) in the deep long 11 sub-member
&#x02018;N&#x02019; represents the total number of statistically analyzed organic pores
but there are few studies on the effect of overpressure on organic macropores in Longmaxi Formation
In the research related to the middle and shallow Longmaxi Formation shale reservoirs in the southern and southeastern Sichuan Basin, the helium porosity is commonly observed to range between 2% and 8%. The variations in porosity are jointly controlled by the formation pressure coefficient and the lithofacies (<a href="#B33">Nguyen et al., 2013</a>; <a href="#B23">Li et al., 2017</a>; <a href="#B32">Nabawy et al., 2022</a>)
as the pressure conditions transit from normal pressure to overpressure
the compaction effect from overlying strata gradually diminishes
maintaining the porosity of shale reservoir at relatively high levels
the compressive strength of siliceous shale
thereby retaining higher porosity and better reservoir capacity
clayey shale and silty shale undergo significant compaction and alteration
leading to a substantial reduction in porosity and reservoir capacity
and they ultimately transform into cap rocks
When normal pressure shifts to overpressure
the compaction intensity of clayey shale significantly decreases
resulting in a notable increase in porosity
sometimes even surpassing that of siliceous shale
clayey shale may also exhibit favorable reservoir capacity under overpressure conditions
This observation indicates that the development of overpressure significantly improves the porosity and quality of clayey shale
Comparison of pore volume in the long 11 sub-member shale reservoir under different pressure coefficients (A)
and comparison of pore volume in the Clayey and Siliceous shales in the Yongchuan area under overpressure conditions (B)
A detailed study on the formation mechanisms
and the controlling effects on reservoir pore characteristics of strong overpressure have been made and the following conclusions can be reached
The well log curve combination method and the sonic velocity-density crossplot method
sediment burial and hydrocarbon generation history
fluid inclusion paleo-pressure recovery together confirm that hydrocarbon generation expansion is the dominant mechanism for the formation of strong overpressure in the deep Longmaxi Formation shale gas reservoir
Overpressured intervals exhibit the log characteristics of significantly increase of acoustic travel time and high resistivity
the deep Longmaxi Formation shale gas reservoir has been influenced by the effects of kerogen oil generation and retained oil cracking into gas
It experienced three stages: normal pressure (Silurian to Early Triassic)
with corresponding pressure coefficients of 1.08&#x02013;1.09
the initially formed overpressure underwent some adjustment due to temperature reduction and gas escape
Fluid pressure gradually decreased from 138.93&#x02013;140.99 MPa to 70.72&#x02013;94.86 MPa
The pressure coefficient showed a change trend of decreasing first and then increasing
and currently strong overpressure is still maintained
Different degrees of strong overpressure have a significant control on the porosity and pore structure of the shale gas reservoir
Higher pressure coefficients contribute to maintaining high porosity and organic macropores
Deep Wufeng-Longmaxi Formation shale exhibits differences in morphological characteristics
structure and connectivity of organic matter pores
This study provides valuable insights for the further understanding and evaluation of deep shale gas reservoirs
The original contributions presented in the study are included in the article/supplementary material
further inquiries can be directed to the corresponding authors
This research was supported by Science and Technology Management Department of PetroChina &#x0201c;Research on Stress Change
Tectonic Activation and Possible Induced Earthquake Mechanism in Shale Gas Development Zones of South Sichuan&#x0201d; (No
The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest
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The formation and destroyment mechanism of shale gas overpressure and its main controlling factors in Silurian of Sichuan Basin
doi:10.11764/j.issn.1672-1926.2016.05.0924
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Analyses of influences on shale reservoirs of Wufeng-Longmaxi Formation by overpressure in the south-eastern part of Sichuan Basin
<a href="https://doi.org/10.14027/j.cnki.cjxb.2015.04.020">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Analyses+of+influences+on+shale+reservoirs+of+Wufeng-Longmaxi+Formation+by+overpressure+in+the+south-eastern+part+of+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Evolution and implications of shale pore structure characteristics under different preservation conditions
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Analysis on mechanism of abnormal low pressure in Sulige gas field
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Analysis+on+mechanism+of+abnormal+low+pressure+in+Sulige+gas+field,+Ordos+Basin&amp;btnG=">Google Scholar</a>
Early overpressuring in organic-rich shales during burial: evidence from fibrous calcite veins in the Lower Jurassic Shales-with-BEEF Member in the Wessex Basin
<a href="https://doi.org/10.1144/jgs2016-146">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Early+overpressuring+in+organic-rich+shales+during+burial:+evidence+from+fibrous+calcite+veins+in+the+Lower+Jurassic+Shales-with-BEEF+Member+in+the+Wessex+Basin,+UK&amp;btnG=">Google Scholar</a>
Implementation of lithofacies and microfacies types on reservoir quality and heterogeneity of the late cretaceous upper bahariya member in the shurouk field
<a href="https://doi.org/10.1016/j.jseaes.2021.105014">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Implementation+of+lithofacies+and+microfacies+types+on+reservoir+quality+and+heterogeneity+of+the+late+cretaceous+upper+bahariya+member+in+the+shurouk+field,+shoushan+basin,+north+western+desert,+Egypt&amp;btnG=">Google Scholar</a>
The role of fluid pressure and diagenetic cements for porosity preservation in Triassic fluvial reservoirs of the Central Graben
<a href="https://doi.org/10.1306/01151311163">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+role+of+fluid+pressure+and+diagenetic+cements+for+porosity+preservation+in+Triassic+fluvial+reservoirs+of+the+Central+Graben,+North+Sea&amp;btnG=">Google Scholar</a>
Temperature and origin of fluid inclusions in shale veins of Wufeng&#x02013;Longmaxi Formations
South China: implications for shale gas preservation and enrichment
<a href="https://doi.org/10.1016/j.petrol.2020.107329">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Temperature+and+origin+of+fluid+inclusions+in+shale+veins+of+Wufeng–Longmaxi+Formations,+Sichuan+Basin,+South+China:+implications+for+shale+gas+preservation+and+enrichment&amp;btnG=">Google Scholar</a>
A preliminary study on the characterization and controlling factors of porosity and pore structure of the Permian shales in Lower Yangtze region
<a href="https://doi.org/10.1016/j.coal.2015.05.005">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+preliminary+study+on+the+characterization+and+controlling+factors+of+porosity+and+pore+structure+of+the+Permian+shales+in+Lower+Yangtze+region,+Eastern+China&amp;btnG=">Google Scholar</a>
Quantitative reconstruction of formation paleo-pressure in sedimentary basins and case studies
<a href="https://doi.org/10.1007/s11430-019-9556-8">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Quantitative+reconstruction+of+formation+paleo-pressure+in+sedimentary+basins+and+case+studies&amp;btnG=">Google Scholar</a>
Characterization of micro-pore throats in the shale gas reservoirs of Zhaotong national shale gas demonstration area
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characterization+of+micro-pore+throats+in+the+shale+gas+reservoirs+of+Zhaotong+national+shale+gas+demonstration+area&amp;btnG=">Google Scholar</a>
Shear mechanical properties of anchored rock mass under impact load
doi:10.13532/j.jmsce.cn10-1638/td.20211014.001
<a href="https://doi.org/10.13532/j.jmsce.cn10-1638/td.20211014.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Shear+mechanical+properties+of+anchored+rock+mass+under+impact+load&amp;btnG=">Google Scholar</a>
The whole apertures of deeply buried Wufeng&#x02043;Longmaxi Formation shale and their controlling factors in Luzhou district
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+whole+apertures+of+deeply+buried+Wufeng⁃Longmaxi+Formation+shale+and+their+controlling+factors+in+Luzhou+district,+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Shale gas exploration and development in China: current status
<a href="https://doi.org/10.1021/acs.energyfuels.0c04131">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Shale+gas+exploration+and+development+in+China:+current+status,+geological+challenges,+and+future+directions&amp;btnG=">Google Scholar</a>
Pressure evolution of deep shale gas reservoirs in Wufeng-Longmaxi formation
southeast Sichuan Basin and its geological significance
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pressure+evolution+of+deep+shale+gas+reservoirs+in+Wufeng-Longmaxi+formation,+Lintanchang+area,+southeast+Sichuan+Basin+and+its+geological+significance&amp;btnG=">Google Scholar</a>
Origin and evolution of overpressure in shale gas reservoirs of the upper ordovician Wufeng Formation&#x02013;lower silurian Longmaxi Formation in the Sichuan Basin
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Origin+and+evolution+of+overpressure+in+shale+gas+reservoirs+of+the+upper+ordovician+Wufeng+Formation–lower+silurian+Longmaxi+Formation+in+the+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Evidence for overpressure generation by kerogen-to-gas maturation in the northern Malay Basin
<a href="https://doi.org/10.1306/09041212032">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Evidence+for+overpressure+generation+by+kerogen-to-gas+maturation+in+the+northern+Malay+Basin&amp;btnG=">Google Scholar</a>
The development features and formation mechanisms of abnormal high formation pressure in southern Junggar region
<a href="https://doi.org/10.3321/j.issn:1000-0747.2003.01.008">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+development+features+and+formation+mechanisms+of+abnormal+high+formation+pressure+in+southern+Junggar+region&amp;btnG=">Google Scholar</a>
Stratigraphic sequence and sedimentary characteristics of lower silurian Longmaxi Formation in Sichuan Basin and its peripheral areas
<a href="https://doi.org/10.1016/j.ngib.2015.07.014">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Stratigraphic+sequence+and+sedimentary+characteristics+of+lower+silurian+Longmaxi+Formation+in+Sichuan+Basin+and+its+peripheral+areas&amp;btnG=">Google Scholar</a>
Overpressure in shale gas reservoirs of Wufeng-Longmaxi formations
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Overpressure+in+shale+gas+reservoirs+of+Wufeng-Longmaxi+formations,+Fuling+area,+southeastern+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Coronavirus disease 2019 outbreak in Beijing&#x00027;s Xinfadi Market
China: a modeling study to inform future resurgence response
<a href="https://doi.org/10.1186/s40249-021-00843-2">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Coronavirus+disease+2019+outbreak+in+Beijing's+Xinfadi+Market,+China:+a+modeling+study+to+inform+future+resurgence+response&amp;btnG=">Google Scholar</a>
Maceral evolution of lacustrine shale and its effects on the development of organic pores during low mature to high mature stage: a case study from the Qingshankou Formation in northern Songliao Basin
<a href="https://doi.org/10.1016/j.petsci.2023.08.025">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Maceral+evolution+of+lacustrine+shale+and+its+effects+on+the+development+of+organic+pores+during+low+mature+to+high+mature+stage:+a+case+study+from+the+Qingshankou+Formation+in+northern+Songliao+Basin,+northeast+China&amp;btnG=">Google Scholar</a>
Pore structure characteristics and main controlling factors of the ultra-deep shales of the Wufeng-Longmaxi Formation in Eastern Sichuan Basin
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+structure+characteristics+and+main+controlling+factors+of+the+ultra-deep+shales+of+the+Wufeng-Longmaxi+Formation+in+Eastern+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Basic characteristics of key interfaces in upper ordovician Wufeng Formation &#x02013; lower silurian Longmaxi Formation in Sichuan Basin and its periphery
<a href="https://doi.org/10.1016/s1876-3804(22)60003-x">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Basic+characteristics+of+key+interfaces+in+upper+ordovician+Wufeng+Formation+–+lower+silurian+Longmaxi+Formation+in+Sichuan+Basin+and+its+periphery,+SW+China&amp;btnG=">Google Scholar</a>
Fluid inclusion evidence for extreme overpressure induced by gas generation in sedimentary basins
<a href="https://doi.org/10.1130/g49848.1">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fluid+inclusion+evidence+for+extreme+overpressure+induced+by+gas+generation+in+sedimentary+basins&amp;btnG=">Google Scholar</a>
Reservoir pressure prediction for marine organic-rich shale: a case study of the Upper Ordovician Wufeng-Lower Silurian Longmaxi shale in Fuling shale gas field
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Reservoir+pressure+prediction+for+marine+organic-rich+shale:+a+case+study+of+the+Upper+Ordovician+Wufeng-Lower+Silurian+Longmaxi+shale+in+Fuling+shale+gas+field,+NE+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Petrographic characterization and maceral controls on porosity in overmature marine shales: examples from ordovician-silurian shales in China and the U.S
<a href="https://doi.org/10.1155/2021/5582262">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Petrographic+characterization+and+maceral+controls+on+porosity+in+overmature+marine+shales:+examples+from+ordovician-silurian+shales+in+China+and+the+U.S&amp;btnG=">Google Scholar</a>
Mechanism and controlling factors on methane yields catalytically generated from low-mature source rocks at low temperatures (60&#x02013;140&#x000b0;C) in laboratory and sedimentary basins
<a href="https://doi.org/10.3389/feart.2022.889302">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mechanism+and+controlling+factors+on+methane+yields+catalytically+generated+from+low-mature+source+rocks+at+low+temperatures+(60–140°C)+in+laboratory+and+sedimentary+basins&amp;btnG=">Google Scholar</a>
Bedding-parallel calcite veins indicate hydrocarbon&#x02013;water&#x02013;rock interactions in the over-mature Longmaxi shales
<a href="https://doi.org/10.1016/j.marpetgeo.2021.105303">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Bedding-parallel+calcite+veins+indicate+hydrocarbon–water–rock+interactions+in+the+over-mature+Longmaxi+shales,+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Fluid activity and pressure evolution process of wufeng-longmaxi shales
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fluid+activity+and+pressure+evolution+process+of+wufeng-longmaxi+shales,+southern+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Organic pores in deep shale controlled by macerals: classification and pore characteristics of organic matter components in Wufeng Formation-Longmaxi Formation of the Sichuan Basin
<a href="https://doi.org/10.3787/j.issn.1000-0976.2021.09.003">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Organic+pores+in+deep+shale+controlled+by+macerals:+classification+and+pore+characteristics+of+organic+matter+components+in+Wufeng+Formation-Longmaxi+Formation+of+the+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Influence of tectonic uplift-erosion on formation pressure
<a href="https://doi.org/10.1007/s12182-010-0094-9">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Influence+of+tectonic+uplift-erosion+on+formation+pressure&amp;btnG=">Google Scholar</a>
Pore structure characteristics of lower Silurian shales in the southern Sichuan Basin
China: insights to pore development and gas storage mechanism
<a href="https://doi.org/10.1016/j.coal.2015.12.015">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+structure+characteristics+of+lower+Silurian+shales+in+the+southern+Sichuan+Basin,+China:+insights+to+pore+development+and+gas+storage+mechanism&amp;btnG=">Google Scholar</a>
Organic carbon content correction and overpressure genesis analysis for overpressure strata of Dongying Formation in Bozhong Sag
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Organic+carbon+content+correction+and+overpressure+genesis+analysis+for+overpressure+strata+of+Dongying+Formation+in+Bozhong+Sag&amp;btnG=">Google Scholar</a>
Main factors controlling marine shale gas enrichment and high-yield wells in South China: a case study of the Fuling shale gas field
<a href="https://doi.org/10.1016/j.marpetgeo.2019.01.024">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Main+factors+controlling+marine+shale+gas+enrichment+and+high-yield+wells+in+South+China:+a+case+study+of+the+Fuling+shale+gas+field&amp;btnG=">Google Scholar</a>
Overpressure generation and evolution in deep Longmaxi Formation Shale reservoir in southern Sichuan Basin: influences on pore development
<a href="https://doi.org/10.3390/en16062533">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Overpressure+generation+and+evolution+in+deep+Longmaxi+Formation+Shale+reservoir+in+southern+Sichuan+Basin:+influences+on+pore+development&amp;btnG=">Google Scholar</a>
Normal pressure formation mechanism of Longmaxi shale gas in Pengshui and its adjacent areas
doi:10.13809/j.cnki.cn32-1825/te.2020.01.002
<a href="https://doi.org/10.13809/j.cnki.cn32-1825/te.2020.01.002">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Normal+pressure+formation+mechanism+of+Longmaxi+shale+gas+in+Pengshui+and+its+adjacent+areas&amp;btnG=">Google Scholar</a>
Natural fractures and their influence on shale gas enrichment in Sichuan Basin
<a href="https://doi.org/10.1016/j.jngse.2015.11.048">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Natural+fractures+and+their+influence+on+shale+gas+enrichment+in+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
An equation for determining methane densities in fluid inclusions with Raman shifts
<a href="https://doi.org/10.1016/j.gexplo.2015.12.003">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=An+equation+for+determining+methane+densities+in+fluid+inclusions+with+Raman+shifts&amp;btnG=">Google Scholar</a>
Unique chemical and isotopic characteristics and origins of natural gases in the Paleozoic marine formations in the Sichuan Basin
SW China: isotope fractionation of deep and high mature carbonate reservoir gases
<a href="https://doi.org/10.1016/j.marpetgeo.2017.02.010">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Unique+chemical+and+isotopic+characteristics+and+origins+of+natural+gases+in+the+Paleozoic+marine+formations+in+the+Sichuan+Basin,+SW+China:+isotope+fractionation+of+deep+and+high+mature+carbonate+reservoir+gases&amp;btnG=">Google Scholar</a>
Mineral composition and seal condition implicated in pore structure development of organic-rich Longmaxi shales
<a href="https://doi.org/10.1016/j.marpetgeo.2018.09.009">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mineral+composition+and+seal+condition+implicated+in+pore+structure+development+of+organic-rich+Longmaxi+shales,+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
Advances in the origin of overpressures in sedimentary basins
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Advances+in+the+origin+of+overpressures+in+sedimentary+basins&amp;btnG=">Google Scholar</a>
Micro-layers division and fine reservoirs contrast of lower silurian Longmaxi Formation shale
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Micro-layers+division+and+fine+reservoirs+contrast+of+lower+silurian+Longmaxi+Formation+shale,+Sichuan+Basin,+SW+China&amp;btnG=">Google Scholar</a>
A new capillary pressure model for fractal porous media using percolation theory
<a href="https://doi.org/10.1016/j.jngse.2017.02.033">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+new+capillary+pressure+model+for+fractal+porous+media+using+percolation+theory&amp;btnG=">Google Scholar</a>
Yin J and Qu J (2024) Formation and evolution of shale overpressure in deep Wufeng-Longmaxi Formation in southern Sichuan basin and its influence on reservoir pore characteristics
Received: 23 January 2024; Accepted: 02 April 2024;Published: 25 April 2024
Copyright &#x000a9; 2024 Sun, Shi, Dong, Bai, Wei, Yin and Qu. This is an open-access article distributed under the terms of the <a rel="license" href="http://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution License (CC BY).</a> The use
&#x0002a;Correspondence: Shasha Sun, <a id="encmail">c3Vuc3M2OUBwZXRyb2NoaW5hLmNvbS5jbg==</a>; Zhensheng Shi, <a id="encmail">c2hpenM2OUBwZXRyb2NoaW5hLmNvbS5jbg==</a>
Volume 10 - 2022 | <a class="ArticleLayoutHeader__info__doi" href="https://doi.org/10.3389/feart.2022.1033407">https://doi.org/10.3389/feart.2022.1033407</a>
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The stress-strain relationship in shales is generally time-dependent
This concerns their long-term deformation in unconventional reservoirs
and its influence on the in situ stress state therein
This paper presents an experimental investigation on the time-dependent deformation of the Longmaxi shale gas shale
A series of creep experiments subject the shale samples to long-term
It is found that the shale samples exhibit varying degrees of time-dependent deformation
which can be adequately described by a power-law function of time
The experimental results establish the relationship between the elastic Young&#x02019;s modulus and viscoplastic constitutive parameters
which are different from previous those derived from North American shales
Based on this viscoplastic constitutive model
the stress relaxation and the differential stress accumulation over geologic time scales can be estimated
It is found that linear elasticity substantially overestimates the differential stress accumulation predicted in the context of viscoplastic relaxation
The characterized viscoplasticity and stress relaxation are of vital importance for various geomechanical problems in shale reservoirs
The mechanical properties of shales are significantly different from those of common rock types (e.g.
sandstones and carbonates) characterized by heterogeneity
Challenges remain when conventional concepts and models (such as linear elasticity) are applied to infer the geomechanical properties and in situ stress in shale reservoirs
quantifying the time-dependent response of shales is of vital importance to in situ stress prediction and other geomechanical applications
Considering the different tectonic environments
it is not clear if the empirical relations derived from North America shales can be directly applied to other shale types
such as the Wufeng-Longmaxi shale investigated in this paper
In this study, we performed a series of multi-step creep experiments on the shale samples from the Longmaxi formation, a major unconventional play in southwestern China (<a href="#B39">Zou et al., 2015</a>; <a href="#B5">Dong et al., 2018</a>)
Based on the laboratory triaxial creep experiments
the time-dependent behavior of the Longmaxi shale samples was investigated considering the effect of hydrostatic loading
Utilizing the theory of linear viscoelasticity
the time-dependent constitutive relation was established for the Wufeng-Longmaxi shale samples
a new empirical relation was proposed to relate the constitutive parameters to the elastic properties
Then the laboratory-derived viscoplastic stress relaxation response was extrapolated
facilitating an estimation of the in situ stress over geologic time scales
a series of integrated well logs are available from the depth of 1950&#x02013;2300&#x000a0;m in Well 1
characteristic of the regional geology and reservoir lithofacies
It has been confirmed that the clay-rich Wufeng-Longmaxi formations are the target of the shale gas play
showing the potential to yield economic hydrocarbon production
Integrated geophysical logs of Well 1: (A) Gamma ray; (B) Element Capture Spectroscopy (ECS); (C) Density; (D) Sonic log derived Young&#x02019;s modulus; (E) Sonic log derived Poisson&#x02019;s ratio
The coring depths of seven shale samples from Well 1 are shown with &#x0201c;H&#x0201d; and &#x0201c;V&#x0201d; denoting horizontal and vertical samples
the stratigraphic column is also shown where &#x0201c;L&#x0201d;
the compositional log via Element Capture Spectroscopy (ECS) indicates systematically higher clay contents and lower QFP contents (volume percentage) than those of the samples from Well 1
Such inconsistency may be attributed to the differences in scale and measurement methods
Before performing the creep experiments on these samples
two shale samples (S1 and S2) without detailed coring information were tested for calibration purposes
Mineral composition and experimental data of the shale samples used in the multi-step creep experiments
&#x0201c;H&#x0201d; and &#x0201c;V&#x0201d; denote horizontal and vertical samples
FIGURE 2. Ternary plot of the mineral composition (in volume fraction) for several representative samples (squares) tested in this study. &#x0201c;H&#x0201d; and &#x0201c;V&#x0201d; denote horizontal and vertical samples, respectively. For reference, the mineral composition of different lithofacies in Well 1 is shown as dots with colors indicated by the stratigraphic column in <a href="#F1">Figure 1</a>
the creep response of Sample S2 was measured at three differential stress levels (20
and 60&#x000a0;MPa) under the confining pressure of 20&#x000a0;MPa
(A) Differential stress and axial/lateral strains evolving with time during the multi-step creep experiment (Sample: S2
the stress was held for about 1 day (24&#x000a0;h)
while the stress for the last step was held for about 6&#x000a0;days
Detailed information of the strains evolving with time is shown in (B&#x02013;E): (B) hydrostatic stage
(C&#x02013;E) differential stress stages with differential stresses of 20
Arrows represent the increase or decrease of the lateral strain during the &#x0201c;instantaneous&#x0201d; loading
Note that data with light color denote the application of the confining pressure or differential stresses
Also note the scale difference for the axial and lateral strain in (B&#x02013;E)
the recorded differential stress and strains of Sample S2 are shown as a function of time during the multi-step creep experiment
the applied confining pressures and differential stresses of the tests in this study are detailed
the close-up of a time interval around 5&#x000d7;105&#x000a0;s clearly shows the details of the data fluctuations
Regression to the data yields an average period of about 2000&#x000a0;s
the compositional difference could mask the orientation effect predicted by the transverse isotropy model
SEM micrographs of two thin-sections corresponding to the same depth as the samples 1&#x02013;5&#x000a0;H and 1&#x02013;6&#x000a0;V
(B) Micrograph shows the abundance of calcite wrapped by clay minerals
the Young&#x02019;s modulus values of each sample are summarized
Relationship of the cumulative differential stress and total axial strain for three pairs of shale samples
Each pair of samples were retrieved from the same depth
Power-law constitutive parameters for Longmaxi shale sample
In <a href="#F7">Figure 7</a>, the creep compliance data for the three differential stress steps of Sample S2 are plotted versus time in the log-log space. Each set of data shows an increasing trend with the logarithm of time. As with the strain data in <a href="#F3">Figure 3</a>
the creep compliance data also feature fluctuations with decreasing degree with time
When the holding time is sufficiently long
the compliance data starts to show a linear trend
For the same sample under different differential stresses
it displays remarkably different creep compliance responses by the individual slopes
the experimental data can be fitted by the widely-used power-law function:
Relationships of creep compliance (J) and time (t) for three differential stress levels (20
60&#x000a0;MPa) shown in the log-log space (Sample: S2
The grey data is the first 1000&#x000a0;s which is not considered in the linear regression
The determined viscoplastic constitutive parameters (B and n) listed in <a href="#T2">Table 2</a> are now plotted in <a href="#F8">Figure 8</a>
Comparison between each well shows that these samples
although collected from different wells and depths
Samples S1 and S2 and Well 3 samples possess relatively lower B values
whereas the B values of Well 2 samples span a higher range (0.04&#x02013;0.1) and Well 1 samples possess the widest range of B values (0.01&#x02013;0.12)
both Well 1 samples and Well 2 samples show that the vertical samples have higher B values and lower n values than horizontal samples
indicating anisotropy in their viscoplastic properties
the samples from Well 3 do not show apparent anisotropy from the laboratory results
Summary of the constitutive parameters of all shale samples
it can be seen that the vertical samples are more compliant than the horizontal samples
which is generally consistent with the theoretical prediction of the transverse isotropy model
Relationship of 1/B and Young&#x02019;s modulus derived from the multi-step creep experiments
calcite) is likely accompanied by the abundant micro-pores
which may often contain fluids as suggested by the overpressure in the Wufeng-Longmaxi formation
it is inferred that the abundance of stiff minerals contributes to high Young&#x02019;s modulus as a short-term response
pore reduction/collapse and drainage could take place over a long time
leading to significant creep deformation as a long-term response
Such an inference could plausibly explain the observation that the stiffer samples feature more significant creep behavior
FIGURE 10. Correlation between Young&#x02019;s modulus and the constitutive parameter n for the studied shale samples. For comparison, data of shales from North American (<a href="#B26">Sone and Zoback, 2014a</a>) are also plotted
Following the theory of linear viscoelasticity, we first obtain the relaxation modulus function by performing Laplace transform operations (<a href="#B15">Lakes, 2009</a>; <a href="#B26">Sone and Zoback, 2014a</a>):
<a href="#e2">Eq. 2</a> implies that 1/B is effectively the Young&#x02019;s modulus at t &#x0003d; 1 s, E1s. Note again that, the fitted relation in <a href="#F9">Figure 9</a> yields that the Young&#x02019;s modulus E is 0.7 times of E1s for the studied shale samples. The difference from the empirical relation for the North American shales (<a href="#B26">Sone and Zoback, 2014a</a>) may be due to the limited shale samples or the special microstructure
it should be cautious to directly apply the empirical relation of the North American shales to other shales
Based on the fitted relation between B and Young&#x02019;s modulus
one can derive B values from Young&#x02019;s modulus values which are more accessible from static experiments
With the relaxation modulus function, we can further calculate the stress response with time based on <a href="#eA2">Eq. (A2)</a>
Assuming a constant strain rate &#x003b5;&#x002d9;
where &#x003b5;0 is the accumulated strain over time t, the constant 0.7 is from the relation between 1/B and E shown in <a href="#F9">Figure 9</a>. In particular, the term t&#x02212;n1&#x02212;n is referred to as stress relaxation factor, which quantifies the fraction of the applied elastic stress that remains unrelaxed after a certain time t (<a href="#B19">Ma and Zoback, 2020</a>)
as long as the accumulated strain &#x003b5;0 and Young&#x02019;s modulus E are reasonably constrained
it is able to estimate the in situ stress without knowing the exact tectonic strain history
it is expected that 20% of the applied differential stress relaxes after 0.01&#x000a0;years (about 3&#x02013;4&#x000a0;days) and 50% of the applied stress relaxes after 200&#x000a0;Myr
Stress relaxation factor as a function of the power exponent n for several time scales from several days up to 200 millions of years (Myr)
the constitutive parameters of all the samples are plotted
To estimate the accumulation of differential stress over a certain period of time
a constant strain rate of 10&#x02013;19 and a deformation duration of 150&#x000a0;Myr are prescribed
Note that it is not easy to constrain a reasonable tectonic strain for the studied shale gas play located near the southern margin of the Sichuan Basin due to the complex geologic and tectonic history
The strain rate and deformation duration are only used for illustrative purpose
The predicted magnitude of the differential stress for all samples ranges from 3 up to 20&#x000a0;MPa
the values where the contours intercept with the horizontal axis (n &#x0003d; 0) correspond to the elastic stress accumulation without viscous relaxation
stress relaxation becomes more pronounced as n increases
indicating less accumulation of the differential stress
Stress accumulation (contours) as a function of the constitutive parameters (B and n)
a constant strain rate of 10&#x02013;19 and a deformation duration of 150&#x000a0;Myr are assumed
The constitutive parameters of all studied samples are also plotted
can also be operative so that a more isotropic stress state is attainable over a shorter time scale
a series of laboratory multi-step creep experiments were performed on several Longmaxi shale samples to investigate their time-dependent deformation properties
It is found that studied shale samples exhibit varying degrees of time-dependent strain response
we extrapolated the stress relaxation of the tested samples and calculated the differential stress accumulation over geologic time scales
the following conclusions can be obtained:
1) Under the applied differential stress levels (20&#x02013;60&#x000a0;MPa)
the instantaneous response of all samples is approximately linear and elastic
collected both from the same well and from different wells
exhibit varying degrees of time-dependent deformation
The time-dependent strain response can be well described by a power-law function of time with only two parameters (B and n)
it is found that Samples S1 and S2 and Samples from Well 3 possess relatively lower values of B
whereas the B values of Well 2 samples are higher
all samples fall within the same ranges (0&#x02013;0.04)
Samples from Wells 1 and 2 show that the vertical samples have higher values of B and lower values of n
indicating the anisotropy in the viscoelastic properties
samples from Well 3 do not show apparent anisotropy from the laboratory results
4) The elastic Young&#x02019;s modulus E correlates with both constitutive parameters (B and n)
it is found that higher E generally corresponds to higher n
which means that a stiffer sample (with higher Young&#x02019;s modulus) tends to exhibit more pronounced time-dependent deformation
Such observation is counterintuitive since one would expect larger creep deformation for samples with lower Young&#x02019;s modulus due to more compliant components
further investigation is required in the future
particularly for the microstructure of the samples
5) The degree of stress relaxation over certain time periods is positively related to the constitutive parameter n
the unrelaxed stress decreases with time but the effect of time gradually diminishes so that a significant amount of differential stress relaxes in the initial short period of time
6) Linear elasticity is not adequate to predict the differential stress accumulation over time
The predicted differential stress accumulation is much larger in the absence of viscoelastic relaxation
the magnitude of differential stress is predicted to be 3&#x02013;10&#x000a0;MPa over 150&#x000a0;Myr at a constant strain rate of 10&#x02013;19
the accumulated differential stress is predicted to be 6.8&#x02013;20.3&#x000a0;MPa by linear elasticity
our laboratory experiments reveal the tendency of the long-term deformation of the Longmaxi shale
can be correlated with the elastic Young&#x02019;s modulus
quantifying the transient behavior that can be measured in situ with logs and ex situ in the laboratories
The viscoplastic properties of the Longmaxi shale can be readily extrapolated to the in situ stress estimation over geologic time scales
facilitating a variety of geomechanical applications in the development of unconventional reservoirs
characterizing the in situ state of stress
especially the &#x0201c;bed-to-bed&#x0201d; lithology-controlled stress variations
is critical to optimizing horizontal well trajectory
improving hydraulic fracturing effectiveness
The workflow presented here for the Longmaxi shale reservoir can be potentially applied to other unconventional plays
The original contributions presented in the study are included in the article/Supplementary Material
and GZ contributed in conceiving this research
This project is sponsored by Research Institute of Petroleum Exploration and Development (RIPED)
China National Petroleum Corporation (CNPC) through an international collaborative grant (No
Open access funding provided by ETH Zurich
This study is partly supported by the Swiss National Science Foundation (Grant no.182150)
We thank all editors and reviewers for their constructive comments and suggestions
and GZ were employed by the Research Institute of Petroleum Exploration &#x00026; Development and Key Laboratory of Oil &#x00026; Gas Production
<a href="https://doi.org/10.1016/j.jngse.2012.06.006">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fracture+stimulation+fundamentals&amp;btnG=">Google Scholar</a>
&#x0201c;The geomechanics of a shale play: What makes a shale prospective!,&#x0201d; in Proceeding of the SPE Eastern Regional Meeting
<a href="https://doi.org/10.2118/125525-ms">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+geomechanics+of+a+shale+play:+What+makes+a+shale+prospective!&amp;btnG=">Google Scholar</a>
Time-dependent subsidence associated with drainage-induced compaction in Gulf of Mexico shales bounding a severely depleted gas reservoir
<a href="https://doi.org/10.1306/11111313009">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Time-dependent+subsidence+associated+with+drainage-induced+compaction+in+Gulf+of+Mexico+shales+bounding+a+severely+depleted+gas+reservoir&amp;btnG=">Google Scholar</a>
Viscous creep in room-dried unconsolidated Gulf of Mexico shale (I): Experimental results
<a href="https://doi.org/10.1016/j.petrol.2009.08.018">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Viscous+creep+in+room-dried+unconsolidated+Gulf+of+Mexico+shale+(I):+Experimental+results&amp;btnG=">Google Scholar</a>
Viscous creep in room-dried unconsolidated Gulf of Mexico shale (II): Development of a viscoplasticity model
<a href="https://doi.org/10.1016/j.petrol.2010.03.002">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Viscous+creep+in+room-dried+unconsolidated+Gulf+of+Mexico+shale+(II):+Development+of+a+viscoplasticity+model&amp;btnG=">Google Scholar</a>
&#x0201c;Preston new road: The role of geomechanics in successful drilling of the UK&#x02019;s first horizontal shale gas well,&#x0201d; in Proceeding of the Society of Petroleum Engineers - SPE Europec Featured at 81st EAGE Conference and Exhibition 2019
<a href="https://doi.org/10.2118/195563-ms">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Preston+new+road:+The+role+of+geomechanics+in+successful+drilling+of+the+UK’s+first+horizontal+shale+gas+well&amp;btnG=">Google Scholar</a>
challenges and prospects of shale gas exploration in the Wufeng&#x02013;Longmaxi reservoirs in the Sichuan Basin
<a href="https://doi.org/10.1016/j.ngib.2018.04.011">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Progress,+challenges+and+prospects+of+shale+gas+exploration+in+the+Wufeng–Longmaxi+reservoirs+in+the+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Creep and relaxation of nonlinear viscoelastic materials
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Creep+and+relaxation+of+nonlinear+viscoelastic+materials&amp;btnG=">Google Scholar</a>
Creep and relaxation of nonlinear viscoelastic materials with an introduction to linear viscoelasticity
<a href="https://doi.org/10.1115/1.3424077">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Creep+and+relaxation+of+nonlinear+viscoelastic+materials+with+an+introduction+to+linear+viscoelasticity&amp;btnG=">Google Scholar</a>
&#x0201c;Modeling of proppant embedment: Elastic deformation and creep deformation,&#x0201d; in Proceeding of the SPE Production and Operations Symposium
<a href="https://doi.org/10.2118/157449-ms">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Modeling+of+proppant+embedment:+Elastic+deformation+and+creep+deformation&amp;btnG=">Google Scholar</a>
The creep behavior of standard linear solid
<a href="https://doi.org/10.1002/app.1975.070191028">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+creep+behavior+of+standard+linear+solid&amp;btnG=">Google Scholar</a>
Predicting and monitoring long-term compaction in unconsolidated reservoir sands using a dual power law model
<a href="https://doi.org/10.1190/1.2751501">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Predicting+and+monitoring+long-term+compaction+in+unconsolidated+reservoir+sands+using+a+dual+power+law+model&amp;btnG=">Google Scholar</a>
Tectonic and geological setting of the earthquake hazards in the Changning shale gas development zone
<a href="https://doi.org/10.1016/S1876-3804(19)60262-4">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Tectonic+and+geological+setting+of+the+earthquake+hazards+in+the+Changning+shale+gas+development+zone,+Sichuan+Basin,+SW+China&amp;btnG=">Google Scholar</a>
The World Stress Map database release 2016: Crustal stress pattern across scales
<a href="https://doi.org/10.1016/j.tecto.2018.07.007">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+World+Stress+Map+database+release+2016:+Crustal+stress+pattern+across+scales&amp;btnG=">Google Scholar</a>
Crustal stress pattern in China and its adjacent areas
<a href="https://doi.org/10.1016/j.jseaes.2017.07.005">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Crustal+stress+pattern+in+China+and+its+adjacent+areas&amp;btnG=">Google Scholar</a>
&#x02018;Deformation of earth materials&#x02019;
an introduction to the rheology of Solid Earth
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=‘Deformation+of+earth+materials’,+an+introduction+to+the+rheology+of+Solid+Earth&amp;btnG=">Google Scholar</a>
Review of stress field studies in Sichuan-Yunnan region
<a href="https://doi.org/10.6038/PG2021FF0171">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Review+of+stress+field+studies+in+Sichuan-Yunnan+region&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1017/CBO9780511626722">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Viscoelastic+materials&amp;btnG=">Google Scholar</a>
The December 2018 ML 5.7 and January 2019 ML 5.3 earthquakes in South Sichuan basin induced by shale gas hydraulic fracturing
<a href="https://doi.org/10.1785/0220190029">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+December+2018+ML+5.7+and+January+2019+ML+5.3+earthquakes+in+South+Sichuan+basin+induced+by+shale+gas+hydraulic+fracturing&amp;btnG=">Google Scholar</a>
and marcellus shale,&#x0201d; in Proceeding of the 46th US Rock Mechanics/Geomechanics Symposium 2012
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Creep+behavior+of+barnett,+haynesville,+and+marcellus+shale&amp;btnG=">Google Scholar</a>
Lithology-controlled stress variations of Longmaxi shale&#x02013;Example of an appraisal wellbore in the Changning area
<a href="https://doi.org/10.1016/j.rockmb.2022.100002">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Lithology-controlled+stress+variations+of+Longmaxi+shale–Example+of+an+appraisal+wellbore+in+the+Changning+area&amp;btnG=">Google Scholar</a>
Lithology-controlled stress variations and pad-scale faults: A case study of hydraulic fracturing in the woodford shale
<a href="https://doi.org/10.1190/GEO2017-0044.1">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Lithology-controlled+stress+variations+and+pad-scale+faults:+A+case+study+of+hydraulic+fracturing+in+the+woodford+shale,+Oklahoma&amp;btnG=">Google Scholar</a>
Predicting lithology-controlled stress variations in the woodford shale from well log data via viscoplastic relaxation
<a href="https://doi.org/10.2118/201232-PA">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Predicting+lithology-controlled+stress+variations+in+the+woodford+shale+from+well+log+data+via+viscoplastic+relaxation&amp;btnG=">Google Scholar</a>
Specific surface area: A reliable predictor of creep and stress relaxation in gas shales
<a href="https://doi.org/10.1190/tle40110815.1">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Specific+surface+area:+A+reliable+predictor+of+creep+and+stress+relaxation+in+gas+shales&amp;btnG=">Google Scholar</a>
The interrelationships between overpressure mechanisms and in-situ stresses
<a href="https://doi.org/10.1306/m76870c2">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+interrelationships+between+overpressure+mechanisms+and+in-situ+stresses&amp;btnG=">Google Scholar</a>
Evaluating the subsidence above gas reservoirs with an elasto-viscoplastic constitutive law
<a href="https://doi.org/10.1016/j.gete.2021.100246">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Evaluating+the+subsidence+above+gas+reservoirs+with+an+elasto-viscoplastic+constitutive+law.+Laboratory+evidences+and+case+histories&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1007/978-94-007-5545-1">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Materials+science+for+structural+geology&amp;btnG=">Google Scholar</a>
Comparison of short-term and long-term creep experiments in shales and carbonates from unconventional gas reservoirs
<a href="https://doi.org/10.1007/s00603-018-1444-y">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Comparison+of+short-term+and+long-term+creep+experiments+in+shales+and+carbonates+from+unconventional+gas+reservoirs&amp;btnG=">Google Scholar</a>
Creep of posidonia shale at elevated pressure and temperature
<a href="https://doi.org/10.1007/s00603-017-1295-y">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Creep+of+posidonia+shale+at+elevated+pressure+and+temperature&amp;btnG=">Google Scholar</a>
Time-dependent deformation of shale gas reservoir rocks and its long-term effect on the in situ state of stress
<a href="https://doi.org/10.1016/j.ijrmms.2014.04.002">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Time-dependent+deformation+of+shale+gas+reservoir+rocks+and+its+long-term+effect+on+the+in+situ+state+of+stress&amp;btnG=">Google Scholar</a>
Viscous relaxation model for predicting least principal stress magnitudes in sedimentary rocks
<a href="https://doi.org/10.1016/j.petrol.2014.09.022">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Viscous+relaxation+model+for+predicting+least+principal+stress+magnitudes+in+sedimentary+rocks&amp;btnG=">Google Scholar</a>
doi:10.1130/0091-7613(2000)028&#x0003c;0399:hfktcs&#x0003e;2.3.co;2
<a href="https://doi.org/10.1130/0091-7613(2000)028%3C0399:hfktcs%3E2.3.co;2">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=How+faulting+keeps+the+crust+strong&amp;btnG=">Google Scholar</a>
&#x0201c;Application of anisotropic wellbore stability model and unconventional fracture model for lateral landing and wellbore trajectory optimization: A case study of shale gas in jingmen area
China,&#x0201d; in Proceeding of the International Petroleum Technology Conference 2019
<a href="https://doi.org/10.2523/19368-ms">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Application+of+anisotropic+wellbore+stability+model+and+unconventional+fracture+model+for+lateral+landing+and+wellbore+trajectory+optimization:+A+case+study+of+shale+gas+in+jingmen+area,+China&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.2118/16402-pa">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=In-situ+stresses+in+low-permeability,+nonmarine+rocks&amp;btnG=">Google Scholar</a>
Inherent transversely isotropic elastic parameters of over-consolidated shale measured by ultrasonic waves and their comparison with static and acoustic in situ log measurements
<a href="https://doi.org/10.1088/1742-2132/5/1/011">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Inherent+transversely+isotropic+elastic+parameters+of+over-consolidated+shale+measured+by+ultrasonic+waves+and+their+comparison+with+static+and+acoustic+in+situ+log+measurements&amp;btnG=">Google Scholar</a>
&#x0201c;Variation of the least principal stress with depth and its effect on vertical hydraulic fracture propagation during multi-stage hydraulic fracturing,&#x0201d; in Proceeding of the 53rd U.S
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Variation+of+the+least+principal+stress+with+depth+and+its+effect+on+vertical+hydraulic+fracture+propagation+during+multi-stage+hydraulic+fracturing&amp;btnG=">Google Scholar</a>
&#x0201c;Fracture gradient prediction using the viscous relaxation model and its relation to out-of-zone microseismicity,&#x0201d; in Proceedings - SPE Annual Technical Conference and Exhibition
<a href="https://doi.org/10.2118/174782-ms">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fracture+gradient+prediction+using+the+viscous+relaxation+model+and+its+relation+to+out-of-zone+microseismicity&amp;btnG=">Google Scholar</a>
The role of preexisting fractures and faults during multistage hydraulic fracturing in the Bakken Formation
<a href="https://doi.org/10.1190/INT-2013-0158.1">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+role+of+preexisting+fractures+and+faults+during+multistage+hydraulic+fracturing+in+the+Bakken+Formation&amp;btnG=">Google Scholar</a>
Viscoplastic deformation of the bakken and adjacent formations and its relation to hydraulic fracture growth
<a href="https://doi.org/10.1007/s00603-015-0866-z">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Viscoplastic+deformation+of+the+bakken+and+adjacent+formations+and+its+relation+to+hydraulic+fracture+growth&amp;btnG=">Google Scholar</a>
Global frictional equilibrium via stochastic
<a href="https://doi.org/10.1029/2020JB021404">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Global+frictional+equilibrium+via+stochastic,+local+coulomb+frictional+slips&amp;btnG=">Google Scholar</a>
&#x0201c;Advanced modeling of production induced stress change impact on wellbore stability of infill well drilling in unconventional reservoirs,&#x0201d; in Proceeding of the SPE/AAPG/SEG Unconventional Resources Technology Conference 2018
<a href="https://doi.org/10.15530/urtec-2018-2889495">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Advanced+modeling+of+production+induced+stress+change+impact+on+wellbore+stability+of+infill+well+drilling+in+unconventional+reservoirs&amp;btnG=">Google Scholar</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Unconventional+reservoir+geomechanics&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1016/S1876-3804(15)30072-0">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Shale+gas+in+China:+Characteristics,+challenges+and+prospects+(I)&amp;btnG=">Google Scholar</a>
For a linear viscoelastic medium, the strain (or stress) response scales linearly with the applied stress (or strain), which favors the use of linear superposition (often referred to as &#x0201c;Boltzmann superposition&#x0201d;) (<a href="#B15">Lakes, 2009</a>; <a href="#B53">Findley and Davis, 2013</a>)
the total strain (or stress) response to a multiple-step stress (or strain) input can be simply obtained as the sum of individual strain (or stress) responses to each step
Assuming the stress (or strain) inputs are infinitesimal
Boltzmann superposition allows us to calculate the strain (or stress) response in an integral form:
in which Jt is the creep compliance function describing the time-dependent strain response to a Heaviside input of unit stress
Et is the relaxation modulus function describing the time-dependent stress response to a Heaviside input of unit strain
If Jt and Et, kernel functions, are known, one can obtain the responses to any arbitrary input history by convolving the kernel functions with the derivative of the input history. The relation between Jt and Et is given by taking the Laplace transforms of <a href="#eA1">Eq. (A1)</a> and <a href="#eA2">Eq. (A2)</a>:
Eliminating &#x003b5; and &#x003c3; from both equations further gives:
This equation allows us to obtain one kernel function if the other one is known. For example, if Et is known, Jt can be calculated by the following steps: 1) taking the Laplace transform of Et to obtain Es; 2) using <a href="#eA5">Eq. (A5)</a> to solve for the corresponding creep compliance Js in the Laplace domain; and 3) performing the inverse Laplace transform to obtain the creep compliance Jt in the time domain
Such operations require that the Laplace and inverse Laplace transform are manageable
Et can be obtained according to the known Jt
considering the self-similar characteristics of the creep compliance
power-law function is adopted in this study due to its simple expression and the capability of predicting long-term creep behavior
Comparison of different functions fit to the creep experimental data: (A) Polynomial function with three parameters; (B) Exponential function with three parameters; (C) Hyperbolic function with three parameters; (D) Power-law function with two parameters; (E) Logarithmic function with two parameters; (F) Comparison between the power-law and logarithmic functions
The experimental data are from the differential stress (60&#x000a0;MPa) stage of Sample S2
Zhang S and Ma X (2023) Time-dependent deformation of Wufeng-Longmaxi shale and its implications on the in situ state of stress
Received: 31 August 2022; Accepted: 16 November 2022;Published: 13 January 2023
Copyright &#x000a9; 2023 Cheng, Zhang, Jin, Liu, Jiang, Zhang, Zhang and Ma. This is an open-access article distributed under the terms of the <a rel="license" href="http://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution License (CC BY).</a> The use
&#x0002a;Correspondence: Jiandong Liu, <a id="encmail">bGl1amlhbmRvbmdAcGV0cm9jaGluYS5jb20uY24=</a>; Shihuai Zhang, <a id="encmail">emhhbmdzaGlAZXRoei5jaA==</a>, <a id="encmail">c2hpaHVhaXpoYW5nLnhoMUBnbWFpbC5jb20=</a>
Volume 10 - 2022 | <a class="ArticleLayoutHeader__info__doi" href="https://doi.org/10.3389/feart.2022.998958">https://doi.org/10.3389/feart.2022.998958</a>
the microscopic pore characteristics of shale in marine strata are evaluated
Based on field emission scanning electron microscopy (FE-SEM)
low-pressure CO2 adsorption (LP-CO2GA) and high-pressure methane adsorption (HPMA) experiments
the pore characteristics of 12 shales from the Wufeng&#x02013;Longmaxi Formations in northern Yunnan and Guizhou are characterized qualitatively and quantitatively
Fractal Frenkel&#x02013;Halsey&#x02013;Hill (FHH) theory is used to analyse the fractal characteristics
and the adsorption pore characteristics of shale are discussed
The correlation between the fractal dimension and pore structure and adsorption performance is determined
The results show that the total organic carbon (TOC) contents of the 12 shales are in the middle&#x02013;low level
and the shales are generally in the highly mature to overmaturity stage (vitrinite reflectance (Ro) values between 1.80% and 2.51%)
The average clay mineral content is 40.98% (ranging from 24.7% to 63.3%)
and the average quartz content is 29.03% (ranging from 16.8% to 39.6%)
which are consistent with those of marine shale in the Sichuan Basin
FE-SEM and LT-N2GA isotherms reveal a complex shale pore structure and open pore style
mainly ink bottle-shaped and parallel plate-like pores
The total pore volumes (PVs) range from 0.012&#x02013;0.052&#x000a0;cm3/g
and the specific surface area (SSA) values range from 18.112&#x02013;38.466&#x000a0;m2/g
All shale samples have abundant micropores and mesopores
accounting for &#x0003e;90% of the total SSA
with different adsorption characteristics at 0&#x02013;0.5 and 0.5&#x02013;1.0 relative pressures
The fractal dimensions increase with increasing BJH PV and BET SSA and decrease with decreasing average pore diameter (APD)
The fractal dimensions are positively correlated with the TOC and clay mineral contents and negatively correlated with the quartz content
The fractal dimension can be used to evaluate the methane adsorption capacity; the larger the fractal dimension is
the larger the methane adsorption capacity is
Fractal analysis is helpful to better understand the pore structure and adsorption capacity of shale gas reservoirs
few studies have focused on the fractal characteristics of marine shale pores in northern Yunnan and Guizhou
the Wufeng Formation and Longmaxi Formation shales
which have the most exploration potential in northern Yunnan and Guizhou
the pore structure of the Wufeng&#x02013;Longmaxi Formation shale in northern Yunnan and Guizhou was analysed
and the fractal dimension of shale adsorption pores was calculated by the FHH model combined with HPMA experiments
X-ray diffraction (XRD) and related geochemical experiments
pore structure parameters and fractal dimension was discussed to provide research methods and evaluation bases for gas-bearing shale reservoir capacity and exploration evaluation in northern Yunnan and Guizhou and to make positive contributions to improving shale gas exploration and development
Structural map and stratigraphic column of the study area
The northern Yunnan&#x02013;Guizhou region experienced the tectonic and sedimentary evolution of the southern continental margin of the Yangtze shelf from the late Proterozoic to the early Paleozoic, the rift epicontinental sea from the late Paleozoic to the Middle Triassic, and the foreland basin in the Mesozoic (<a href="#B30">Liang et al., 2020</a>)
The two sedimentary assemblages include the marine Sinian&#x02013;Middle Triassic and continental Upper Triassic&#x02013;Lower Cretaceous complete strata
which have large stratigraphic thicknesses and wide distributions
Silurian and Upper Triassic&#x02013;Jurassic strata are clastic rocks
and the other strata are mainly carbonate rocks
Various layers on the surface are exposed to different degrees
and most of the Lower Paleozoic are buried in the belly of the earth
shale gas target interval five mountains&#x02013;the dragon stream group deposit in the south of the study area is missing
for a closed set of deposits were stranded anoxic still water environment
the main lithology is black siliceous mudstone
upwards gradient for grey black&#x02013;grey silty mudstone
calcium Shale is thick and thickens gradually from south to north
12 shale samples of the Wufeng&#x02013;Longmaxi Formations in northern Yunnan and Guizhou were collected
To systematically analyse the micropore structural characteristics and factors influencing the Wufeng&#x02013;Longmaxi Formation shale
a relatively complete experimental scheme was carried out
including the determination of the TOC content and vitrinite reflectance (Ro)
The mineral composition and relative mineral percentage of shale samples were estimated according to the standard SY/T 5163-2018
and the BJH model was used to calculate the PV and pore size distribution (PSD)
The LP-CO2GA experiment was carried out at 273&#x000a0;K under different partial pressures
A more suitable DFT model was used to calculate the volume and pore size distribution of micropores
The HPMA experiment was carried out by a Gravimetric Isotherm Rig 3 adsorption instrument
The experimental standard and test method were based on the standard GB/T 1956&#x02013;2008
The shale samples were screened to the same sizes of 60&#x02013;80 mesh
and the samples were weighed to approximately 80&#x02013;120&#x000a0;g
The methane adsorption isotherms of water equilibrium samples were measured at 50&#x000b0;C and 20&#x000a0;MPa under constant pressure
The methods for calculating the fractal dimension based on LT-N2GA data include the thermodynamic method, fractal Langmuir model, fractal BET model and fractal FHH model (<a href="#B26">Li Y. et al., 2019</a>). Among them, the FHH model is proven to be more concise, effective and reliable and is widely used to analyse the surface roughness and spatial structure of porous media (<a href="#B49">Wang et al., 2015</a>; <a href="#B26">Li Y. et al., 2019</a>; <a href="#B23">Li H. et al., 2022</a>)
The FHH calculation formula based on LT-N2GA data is as follows:
where V is the volume of gas molecules adsorbed at equilibrium pressure p
in cm3/g; Vm is the volume of gas adsorbed by the monolayer
in cm3/g; C is a constant; p0 is the saturated vapour pressure of gas adsorption
in MPa; and A is the coefficient related to the fractal dimension (D)
By calculating the logarithmic slope (lnVand ln(ln(p0/p))) of the adsorption volume and the reciprocal of the relative pressure
and the D of shale adsorption pores can be calculated by the value A:
where D is the fractal dimension and the D value is between 2 and 3. When the value is 2, it represents a completely smooth surface and highly homogeneous pore structure. When the value is 3, it indicates an extremely rough pore surface and an extremely complex pore structure (<a href="#B26">Li Y. et al., 2019</a>; <a href="#B40">Shi et al., 2022</a>)
Geochemical characteristics and mineral composition of shale samples
FE-SEM images of a shale from the Longmaxi Formation (TOC &#x0003d;0.58%
sample 2) [(A) mould pores and organic pores between pyrite particles; (B) irregular organic pores; (C) microcracks with different openings; (D) angular granular endopore]
FE-SEM images of a shale from the Longmaxi Formation (TOC &#x0003d;5.05%
Sample 9) [(A) organic shrinkage cracks and organic pores; (B) organic-clay mineral complexes and organic pores; (C) organic&#x02013;pyrite complex and organic pores; (D) mineral grain edge seams and microcracks that cut through minerals]
the lag loop width of shale samples with high TOC contents is larger than that of shale samples with low TOC contents
indicating that organic matter content has a certain promoting effect on shale pore volume development
The pore structure system of shale may be more complex
which was confirmed by the previous FE-SEM experiment
N2 adsorption&#x02013;desorption isotherms of shale samples
The microscopic pore structure of shale reflects that there are a large number of nanoscale pores in shale
and the shale has a large BET SSA and BJH PV
which can provide abundant storage space for hydrocarbon gas
Pore size distributions obtained from LT-N2GA isotherms
Due to the strong energy and fast equilibrium of CO2 molecules in high-temperature analysis (273&#x000a0;K), CO2 molecules can enter smaller pores, especially those with diameters &#x0003c;2&#x000a0;nm, providing most of the storage space for the absorbed gas (<a href="#B8">Chen et al., 2017</a>; <a href="#B26">Li Y. et al., 2019</a>). The LP-CO2GA isotherms of 12 shale samples are shown in <a href="#F6">Figure 6A</a>
these isotherms have the characteristics of type I isotherms
The adsorbed CO2 of sample 10 is the highest
indicating that the sample contains more micropores
indicating that relatively few micropores are present in the sample
(A) CO2 adsorption isotherms of shale samples and (B) pore size distributions obtained from LP-CO2GA
the micropore development of the sample generally presents a multipeak type
with main peaks of 0.3&#x02013;0.4&#x000a0;nm
indicating a wide distribution range of micropores in shale samples
In the range of 0.3&#x02013;0.9&#x000a0;nm
the pore diameters corresponding to the main peaks are 0.35&#x000a0;nm
LT-N2GA is the low-temperature N2 adsorption; LT-CO2GA is the low-pressure CO2 adsorption; SBET is the BET specific surface area
cm3/g; DN is the average pore width by LT-N2GA
cm3/g; DCO2 is the average pore width by LT-CO2GA
Comparisons of the fractal dimensions of shale samples in different areas
Fractal dimensions derived from the FHH model
the increase in TOC content provides a large amount of storage space for shale gas
thus increasing the overall shale gas content
(A) Isothermal adsorption curves of shale samples and (B) relationships between the TOC and VL of shale samples
Distributions of different scales of pores acquired from LT-N2GA and LP-CO2GA [(A) percentage of the PV; (B) percentage of the pore SSA]
Shale with smaller APD has more micropores and mesopores
and the SSA and total PV are relatively higher
Correlation between pore structure parameters
the smooth surface of quartz has fewer pores
and the SSA and total PV of quartz are smaller
TOC and clay minerals increase porosity together and have a positive effect on the PV and SSA of shale
while quartz has a negative effect on the total PV and SSA of shale
Relationships between pore structure parameters and shale composition [(A) TOC vs BET SSA
(B) TOC vs BJH PV; (C) quartz content vs BET SSA; (D) quartz content vs BJH PV; (E) clay content vs BET SSA
indicating that the factors controlling the D of shale pores in northern Yunnan and Guizhou are more complex
This complexity may be affected by a combination of factors
The factors controlling the D of shale pores in the northern Yunnan and Guizhou areas need to be studied in more detail in the future
Relationships between the shale composition and fractal dimensions (D1 and D2) [(A): TOC vs D1 and D2; (B): quartz content vs D1 and D2; (C): clay content vs D1 and D2; (D): D1 vs D2]
Relationships between the fractal dimensions (D1 and D2) and pore structure parameters [(A) D1 and D2 vs BET SSA; (B) D1 and D2 vs BJH PV; (C) D1 and D2 vs APD]
the larger the SSA and the more favourable the adsorption of methane gas molecules
(A) Relationships between the VL and fractal dimensions (D1 and D2) and (B) relationships between the VL and micropore SSA
Chart showing the adsorption process and the major fractal dimension in (A) sample 1 and (B) sample 10
1) The pores developed in the Wufeng&#x02013;Longmaxi shales are mainly OM pores and intraP pores
According to the adsorption-desorption curve of LT-N2GA
mainly parallel plate-like pores and slit pores are observed
2) Most of the pores are in the 0.3&#x02013;0.9&#x000a0;nm and 2&#x02013;4&#x000a0;nm range
with some pores between 20 and 60&#x000a0;nm
3) The mineralogical compositions and TOC of the Wufeng&#x02013;Longmaxi shales have different impacts on the pore structure parameters
The TOC content has a positive effect on the BET SSA and BJH PV
The BET SSA and BJH PV are positively correlated with the clay mineral content but negatively linearly correlated with the quartz content
4) The pore structure parameters in turn exert different effects on the fractal dimensions D1 and D2
D1 and D2 increase with increasing total PV and SSA and decrease with APD
D1 and D2 have a significant positive correlation with the TOC and clay mineral content and a significant negative correlation with the quartz content
the greater the adsorption capacity of shale
All authors contributed to the article and approved the submitted version
This research was jointly supported by the National Natural Science Foundation of China (Grant No
41472122) and Innovative Team Project of Education Department of Hubei Province (Grant No
We thank PetroChina Exploration and Development Research Institute for picking up the samples
Author FT was employed by PetroChina Coalbed Methane Company
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Adsorption of gases in multimolecular layers
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Characterization of gas shale pore systems by porosimetry
and field emission scanning electron microscopy/transmission electron microscopy image analyses: Examples from the barnett
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The organic matter distribution and methane capacity of the lower cretaceous strata of northeastern British columbia
<a href="https://doi.org/10.1016/j.coal.2006.05.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+organic+matter+distribution+and+methane+capacity+of+the+lower+cretaceous+strata+of+northeastern+British+columbia,+Canada&amp;btnG=">Google Scholar</a>
A comparison of nano-scale pore attributes of Barakar Formation gas shales from Raniganj and Wardha Basin
India using low pressure sorption and FEG-SEM analysis
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A novel approach to identify accessible and inaccessible pores in gas shales using combined low-pressure sorption and SAXS/SANS analysis
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Role of composition and depth on pore attributes of barakar formation gas shales of ib valley
using a combination of low-pressure sorption and image analysis
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Pore structure characterization of different rank coals using N2 and CO2 adsorption and its effect on CH4 adsorption capacity: A case in panguan syncline
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Characterization of tight gas reservoir pore structure using USANS/SANS and gas adsorption analysis
<a href="https://doi.org/10.1016/j.fuel.2011.12.010">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characterization+of+tight+gas+reservoir+pore+structure+using+USANS/SANS+and+gas+adsorption+analysis&amp;btnG=">Google Scholar</a>
Experimental study on isothermal adsorption of methane gas on three shale samples from upper paleozoic strata of the Ordos Basin
<a href="https://doi.org/10.1016/j.petrol.2013.08.048">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Experimental+study+on+isothermal+adsorption+of+methane+gas+on+three+shale+samples+from+upper+paleozoic+strata+of+the+Ordos+Basin&amp;btnG=">Google Scholar</a>
A study on fractal characteristics of lacustrine shales of Qingshankou Formation in the Songliao Basin
northeast China using nitrogen adsorption and mercury injection methods
<a href="https://doi.org/10.1016/j.petrol.2020.107378">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+study+on+fractal+characteristics+of+lacustrine+shales+of+Qingshankou+Formation+in+the+Songliao+Basin,+northeast+China+using+nitrogen+adsorption+and+mercury+injection+methods&amp;btnG=">Google Scholar</a>
Pore structure representations based on nitrogen adsorption experiments and an FHH fractal model: Case study of the block Z shales in the Ordos Basin
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Evolution characteristics of micropore and mesopore of different rank coal and cause of their formation
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Evolution+characteristics+of+micropore+and+mesopore+of+different+rank+coal+and+cause+of+their+formation&amp;btnG=">Google Scholar</a>
Investigation of pore structure and fractal characteristics of the lower silurian Longmaxi shales in Western hunan and Hubei provinces in China
<a href="https://doi.org/10.1016/j.jngse.2015.12.024">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Investigation+of+pore+structure+and+fractal+characteristics+of+the+lower+silurian+Longmaxi+shales+in+Western+hunan+and+Hubei+provinces+in+China&amp;btnG=">Google Scholar</a>
<a name="B16" id="B16"></a>IUPAC (International Union of Pure and Applied Chemistry) (1994)
Physical chemistry division commission on colloid and surface chemistry
subcommittee on characterization of porous solids: Recommendations for the characterization of porous solids (technical report)
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Physical+chemistry+division+commission+on+colloid+and+surface+chemistry,+subcommittee+on+characterization+of+porous+solids:+Recommendations+for+the+characterization+of+porous+solids+(technical+report)&amp;btnG=">Google Scholar</a>
Fractal characteristics of nano-pores in the lower silurian Longmaxi shales from the upper Yangtze platform
<a href="https://doi.org/10.1016/j.marpetgeo.2016.08.023">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fractal+characteristics+of+nano-pores+in+the+lower+silurian+Longmaxi+shales+from+the+upper+Yangtze+platform,+south+China&amp;btnG=">Google Scholar</a>
The whole-aperture pore structure characteristics and its effect on gas content of the Longmaxi Formation shale in the Sichuan basin
<a href="https://doi.org/10.13745/j.esf.2016.02.013">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+whole-aperture+pore+structure+characteristics+and+its+effect+on+gas+content+of+the+Longmaxi+Formation+shale+in+the+Sichuan+basin&amp;btnG=">Google Scholar</a>
The characterization and quantitative analysis of nanopores in unconventional gas reservoirs utilizing FESEM&#x02013;FIB and image processing: An example from the lower Silurian Longmaxi Shale
<a href="https://doi.org/10.1016/j.coal.2014.03.004">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+characterization+and+quantitative+analysis+of+nanopores+in+unconventional+gas+reservoirs+utilizing+FESEM–FIB+and+image+processing:+An+example+from+the+lower+Silurian+Longmaxi+Shale,+upper+Yangtze+region,+China&amp;btnG=">Google Scholar</a>
A comparative study of the micropore structure between the transitional and marine shales in China
<a href="https://doi.org/10.1155/2021/5562532">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+comparative+study+of+the+micropore+structure+between+the+transitional+and+marine+shales+in+China&amp;btnG=">Google Scholar</a>
Investigation of pore structure and fractal characteristics of organicrich shale reservoirs: A case study of lower cambrian qiongzhusi formation in malong block of eastern yunnan province
<a href="https://doi.org/10.1016/j.marpetgeo.2015.11.004">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Investigation+of+pore+structure+and+fractal+characteristics+of+organicrich+shale+reservoirs:+A+case+study+of+lower+cambrian+qiongzhusi+formation+in+malong+block+of+eastern+yunnan+province,+south+China&amp;btnG=">Google Scholar</a>
formation periods and genetic mechanisms of tectonic fractures in the tight gas sandstones reservoir: A case study of xujiahe formation in YB area
<a href="https://doi.org/10.1016/j.petrol.2019.04.007">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characteristics,+formation+periods+and+genetic+mechanisms+of+tectonic+fractures+in+the+tight+gas+sandstones+reservoir:+A+case+study+of+xujiahe+formation+in+YB+area,+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
Pore structure and fractal characteristics of the marine shale of the Longmaxi formation in the changning area
<a href="https://doi.org/10.3389/feart.2022.1018274">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+structure+and+fractal+characteristics+of+the+marine+shale+of+the+Longmaxi+formation+in+the+changning+area,+southern+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
Geological characteristics and controlling factors of deep shale gas enrichment of the Wufeng-Longmaxi formation in the southern Sichuan Basin
<a href="https://doi.org/10.2113/2022/4737801">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geological+characteristics+and+controlling+factors+of+deep+shale+gas+enrichment+of+the+Wufeng-Longmaxi+formation+in+the+southern+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
Micro-pore structure and fractal characteristics of deep shale from Wufeng Formation to Longmaxi formation in jingmen exploration area
<a href="https://doi.org/10.1016/j.jnggs.2022.06.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Micro-pore+structure+and+fractal+characteristics+of+deep+shale+from+Wufeng+Formation+to+Longmaxi+formation+in+jingmen+exploration+area,+Hubei+province,+China&amp;btnG=">Google Scholar</a>
Pore structure and its fractal dimensions of transitional shale: A cross-section from east margin of the Ordos Basin
<a href="https://doi.org/10.1016/j.fuel.2018.12.066">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+structure+and+its+fractal+dimensions+of+transitional+shale:+A+cross-section+from+east+margin+of+the+Ordos+Basin,+China&amp;btnG=">Google Scholar</a>
Multi-scale quantitative characterization of 3-D pore-fracture networks in bituminous and anthracite coals using FIB-SEM tomography and X-ray &#x003bc;-CT
<a href="https://doi.org/10.1016/j.fuel.2017.07.088">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Multi-scale+quantitative+characterization+of+3-D+pore-fracture+networks+in+bituminous+and+anthracite+coals+using+FIB-SEM+tomography+and+X-ray+μ-CT&amp;btnG=">Google Scholar</a>
Study on the pore structure and fractal characteristics of marine and continental shale based on mercury porosimetry
<a href="https://doi.org/10.1016/j.jngse.2018.02.027">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Study+on+the+pore+structure+and+fractal+characteristics+of+marine+and+continental+shale+based+on+mercury+porosimetry,+N2+adsorption+and+NMR+methods&amp;btnG=">Google Scholar</a>
An investigation of the fractal characteristics of the Upper Ordovician Wufeng Formation shale using nitrogen adsorption analysis
<a href="https://doi.org/10.1016/j.jngse.2015.07.023">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=An+investigation+of+the+fractal+characteristics+of+the+Upper+Ordovician+Wufeng+Formation+shale+using+nitrogen+adsorption+analysis&amp;btnG=">Google Scholar</a>
Evaluation of shale gas resource potential of Longmaxi formation in zhaotong national shale gas demonstration area in the northern yunnan-guizhou
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Evaluation+of+shale+gas+resource+potential+of+Longmaxi+formation+in+zhaotong+national+shale+gas+demonstration+area+in+the+northern+yunnan-guizhou&amp;btnG=">Google Scholar</a>
Investigation of pore structure and fractal characteristics of organicrich Yanchang formation shale in central China by nitrogen adsorption/desorption analysis
<a href="https://doi.org/10.1016/j.jngse.2014.11.020">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Investigation+of+pore+structure+and+fractal+characteristics+of+organicrich+Yanchang+formation+shale+in+central+China+by+nitrogen+adsorption/desorption+analysis&amp;btnG=">Google Scholar</a>
Spectrum of pore types and networks in mudrocks and a descriptive classification for matrix-related mudrock pores
<a href="https://doi.org/10.1306/08171111061">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Spectrum+of+pore+types+and+networks+in+mudrocks+and+a+descriptive+classification+for+matrix-related+mudrock+pores&amp;btnG=">Google Scholar</a>
and distribution of nanometer-scale pores in siliceous mudstones of the mississippian barnett shale
<a href="https://doi.org/10.2110/jsr.2009.092">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Morphology,+genesis,+and+distribution+of+nanometer-scale+pores+in+siliceous+mudstones+of+the+mississippian+barnett+shale&amp;btnG=">Google Scholar</a>
Investigation of pore structure and fractal characteristics of marine continental transitional shales from Longtan Formation using MICP
<a href="https://doi.org/10.1016/j.marpetgeo.2019.05.018">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Investigation+of+pore+structure+and+fractal+characteristics+of+marine+continental+transitional+shales+from+Longtan+Formation+using+MICP,+gas+adsorption,+and+NMR+(Guizhou,+China)&amp;btnG=">Google Scholar</a>
Porosity of coal and shale: Insights from gas adsorption and SANS/USANS techniques
<a href="https://doi.org/10.1021/ef300735t">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Porosity+of+coal+and+shale:+Insights+from+gas+adsorption+and+SANS/USANS+techniques&amp;btnG=">Google Scholar</a>
Pore structure characterization of different rank coals using gas adsorption and scanning electron microscopy
<a href="https://doi.org/10.1016/j.fuel.2015.06.050">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+structure+characterization+of+different+rank+coals+using+gas+adsorption+and+scanning+electron+microscopy&amp;btnG=">Google Scholar</a>
Organic nanopore structure and fractal characteristics of Wufeng and lower member of Longmaxi shales in southeastern Sichuan
<a href="https://doi.org/10.1016/j.marpetgeo.2019.03.017">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Organic+nanopore+structure+and+fractal+characteristics+of+Wufeng+and+lower+member+of+Longmaxi+shales+in+southeastern+Sichuan,+China&amp;btnG=">Google Scholar</a>
Reflectance measurements of zooclasts and solid bitumen in lower paleozoic shales
southern scandinavia: Correlation to vitrinite reflectance
<a href="https://doi.org/10.1016/j.coal.2013.03.013">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Reflectance+measurements+of+zooclasts+and+solid+bitumen+in+lower+paleozoic+shales,+southern+scandinavia:+Correlation+to+vitrinite+reflectance&amp;btnG=">Google Scholar</a>
Characterizing the shale gas resource potential of devonian-mississippian strata in the western Canada sedimentary basin: Application of an integrated formation evaluation
<a href="https://doi.org/10.1306/09040707048">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characterizing+the+shale+gas+resource+potential+of+devonian-mississippian+strata+in+the+western+Canada+sedimentary+basin:+Application+of+an+integrated+formation+evaluation&amp;btnG=">Google Scholar</a>
Fractal analysis of pore structures in transitional shale gas reservoirs in the Linxing area
<a href="https://doi.org/10.3389/feart.2022.979039">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fractal+analysis+of+pore+structures+in+transitional+shale+gas+reservoirs+in+the+Linxing+area,+Ordos+Basin&amp;btnG=">Google Scholar</a>
The use of nitrogen adsorption for the characterisation of porous materials
<a href="https://doi.org/10.1016/S0927-7757(01)00612-4">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+use+of+nitrogen+adsorption+for+the+characterisation+of+porous+materials&amp;btnG=">Google Scholar</a>
Nanoscale pore characteristics of the lower cambrian Niutitang Formation shale: A case study from well yuke &#x00023;1 in the southeast of chongqing
<a href="https://doi.org/10.1016/j.coal.2015.11.015">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Nanoscale+pore+characteristics+of+the+lower+cambrian+Niutitang+Formation+shale:+A+case+study+from+well+yuke+#1+in+the+southeast+of+chongqing,+China&amp;btnG=">Google Scholar</a>
Multiscale connectivity characterization of marine shales in southern China by fluid intrusion
<a href="https://doi.org/10.1016/j.marpetgeo.2019.104101">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Multiscale+connectivity+characterization+of+marine+shales+in+southern+China+by+fluid+intrusion,+small-angle+neutron+scattering+(SANS),+and+FIB-sem&amp;btnG=">Google Scholar</a>
Characterization of whole-aperture pore structure and its effect on methane adsorption capacity for transitional shales
<a href="https://doi.org/10.1021/acs.energyfuels.7b03807">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characterization+of+whole-aperture+pore+structure+and+its+effect+on+methane+adsorption+capacity+for+transitional+shales&amp;btnG=">Google Scholar</a>
Characterization of methane adsorption on overmature lower silurian-upper ordovician shales in Sichuan Basin
southwest China: Experimental results and geological implications
<a href="https://doi.org/10.1016/j.coal.2016.01.013">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characterization+of+methane+adsorption+on+overmature+lower+silurian-upper+ordovician+shales+in+Sichuan+Basin,+southwest+China:+Experimental+results+and+geological+implications&amp;btnG=">Google Scholar</a>
A preliminary study on the pore characterization of Lower Silurian black shales in the Chuandong Thrust Fold Belt
southwestern China using low pressure N2 adsorption and FE-SEM methods
<a href="https://doi.org/10.1016/j.marpetgeo.2013.07.008">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+preliminary+study+on+the+pore+characterization+of+Lower+Silurian+black+shales+in+the+Chuandong+Thrust+Fold+Belt,+southwestern+China+using+low+pressure+N2+adsorption+and+FE-SEM+methods&amp;btnG=">Google Scholar</a>
Pore characterization of organic-rich lower cambrian shales in qiannan depression of Guizhou province
<a href="https://doi.org/10.1016/j.marpetgeo.2015.01.004">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+characterization+of+organic-rich+lower+cambrian+shales+in+qiannan+depression+of+Guizhou+province,+southwestern+China&amp;btnG=">Google Scholar</a>
Interpreting pore dimensions in gas shales using a combination of SEM imaging
<a href="https://doi.org/10.1021/acs.energyfuels.9b00442">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Interpreting+pore+dimensions+in+gas+shales+using+a+combination+of+SEM+imaging,+small-angle+neutron+scattering,+and+low-pressure+gas+adsorption&amp;btnG=">Google Scholar</a>
Fractal characteristics of upper cretaceous lacustrine shale from the Songliao Basin
<a href="https://doi.org/10.1016/j.marpetgeo.2015.05.011">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fractal+characteristics+of+upper+cretaceous+lacustrine+shale+from+the+Songliao+Basin,+NE+China&amp;btnG=">Google Scholar</a>
Full-scale pore structure and fractal dimension of the Longmaxi shale from the southern Sichuan Basin: Investigations using FE-SEM
gas adsorption and mercury intrusion porosimetry
<a href="https://doi.org/10.3390/min9090543">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Full-scale+pore+structure+and+fractal+dimension+of+the+Longmaxi+shale+from+the+southern+Sichuan+Basin:+Investigations+using+FE-SEM,+gas+adsorption+and+mercury+intrusion+porosimetry&amp;btnG=">Google Scholar</a>
Fractal characteristics of micro- and mesopores in the Longmaxi shale
<a href="https://doi.org/10.3390/en13061349">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fractal+characteristics+of+micro-+and+mesopores+in+the+Longmaxi+shale&amp;btnG=">Google Scholar</a>
Pore characterization and its impact on methane adsorption capacity for organic-rich marine shales
<a href="https://doi.org/10.1016/j.fuel.2016.04.082">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+characterization+and+its+impact+on+methane+adsorption+capacity+for+organic-rich+marine+shales&amp;btnG=">Google Scholar</a>
X-ray diffraction techniques for mineral identification and mineralogical composition
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=X-ray+diffraction+techniques+for+mineral+identification+and+mineralogical+composition&amp;btnG=">Google Scholar</a>
Pore characterization and the controls of organic matter and quartz on pore structure: Case study of the Niutitang Formation of northern Guizhou province
<a href="https://doi.org/10.1016/j.jngse.2018.11.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+characterization+and+the+controls+of+organic+matter+and+quartz+on+pore+structure:+Case+study+of+the+Niutitang+Formation+of+northern+Guizhou+province,+south+China&amp;btnG=">Google Scholar</a>
Fractal characteristics of shales from a shale gas reservoir in the Sichuan Basin
<a href="https://doi.org/10.1016/j.fuel.2013.07.040">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fractal+characteristics+of+shales+from+a+shale+gas+reservoir+in+the+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
Methane adsorption constrained by pore structure in high-rank coals using FESEM
<a href="https://doi.org/10.1002/ese3.275">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Methane+adsorption+constrained+by+pore+structure+in+high-rank+coals+using+FESEM,+CO2+adsorption,+and+NMRC+techniques&amp;btnG=">Google Scholar</a>
Geochemical composition and microstructure of coal measure shale in the upper permian
China: Implications for methane generation and storage
<a href="https://doi.org/10.1021/acs.energyfuels.2c01975">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geochemical+composition+and+microstructure+of+coal+measure+shale+in+the+upper+permian,+western+Guizhou,+China:+Implications+for+methane+generation+and+storage&amp;btnG=">Google Scholar</a>
A comparative evaluation of coal specific surface area by CO2 and N2 adsorption and its influence on CH4 adsorption capacity at different pore sizes
<a href="https://doi.org/10.1016/j.fuel.2016.06.076">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+comparative+evaluation+of+coal+specific+surface+area+by+CO2+and+N2+adsorption+and+its+influence+on+CH4+adsorption+capacity+at+different+pore+sizes&amp;btnG=">Google Scholar</a>
Pore structure characterization of coal by synchrotron radiation nano-CT
<a href="https://doi.org/10.1016/j.fuel.2017.11.014">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+structure+characterization+of+coal+by+synchrotron+radiation+nano-CT&amp;btnG=">Google Scholar</a>
Enrichment conditions and favorable zone prediction of Wufeng&#x02013;Longmaxi shale gas reservoirs in the northern Yunnan&#x02013;Guizhou provinces
<a href="https://doi.org/10.3787/j.issn.1000-0976.2017.12.004">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Enrichment+conditions+and+favorable+zone+prediction+of+Wufeng–Longmaxi+shale+gas+reservoirs+in+the+northern+Yunnan–Guizhou+provinces,+China&amp;btnG=">Google Scholar</a>
3D characterization and quantitative evaluation of pore-fracture networks of two Chinese coals using FIB-SEM tomography
<a href="https://doi.org/10.1016/j.coal.2017.03.008">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=3D+characterization+and+quantitative+evaluation+of+pore-fracture+networks+of+two+Chinese+coals+using+FIB-SEM+tomography&amp;btnG=">Google Scholar</a>
A comparative study of the nanopore structure characteristics of coals and Longmaxi shales in China
<a href="https://doi.org/10.1002/ese3.458">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+comparative+study+of+the+nanopore+structure+characteristics+of+coals+and+Longmaxi+shales+in+China&amp;btnG=">Google Scholar</a>
2D and 3D nanopore characterization of gas shale in Longmaxi formation based on FIB-SEM
<a href="https://doi.org/10.1016/j.marpetgeo.2016.02.033">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=2D+and+3D+nanopore+characterization+of+gas+shale+in+Longmaxi+formation+based+on+FIB-SEM&amp;btnG=">Google Scholar</a>
Characteristics of nanoscale pore structure of organic-rich Longmaxi shale in northern Yunnan and Guizhou province
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characteristics+of+nanoscale+pore+structure+of+organic-rich+Longmaxi+shale+in+northern+Yunnan+and+Guizhou+province&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1016/S1876-3804(16)30022-2">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Shale+gas+in+China:+Characteristics,+challenges+and+prospects+(II)&amp;btnG=">Google Scholar</a>
Technology and prospects of conventional and unconventional natural gas
<a href="https://doi.org/10.1016/S1876-3804(18)30066-1">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Theory,+Technology+and+prospects+of+conventional+and+unconventional+natural+gas&amp;btnG=">Google Scholar</a>
resource potential and key techniques of unconventional hydrocarbon: On unconventional petroleum geology
<a href="https://doi.org/10.11698/PED.2013.04.01">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geological+concepts,+characteristics,+resource+potential+and+key+techniques+of+unconventional+hydrocarbon:+On+unconventional+petroleum+geology&amp;btnG=">Google Scholar</a>
BET Brunauer&#x02013;Emmett&#x02013;Teller
FE-SEM Field emission scanning electron microscope
Deng Z and Hu H (2023) Pore structure and fractal characteristics of Wufeng&#x02013;Longmaxi formation shale in northern Yunnan&#x02013;Guizhou
Received: 20 July 2022; Accepted: 26 September 2022;Published: 06 January 2023
Copyright &#x000a9; 2023 Wang, Tian, Deng and Hu. This is an open-access article distributed under the terms of the <a rel="license" href="http://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution License (CC BY).</a> The use
&#x0002a;Correspondence: Ze Deng, <a id="encmail">ZGVuZ3plQHBldHJvY2hpbmEuY29tLmNu</a>; Haiyan Hu, <a id="encmail">MTA2NDA2OTMzNEBxcS5jb20=</a>
Volume 10 - 2022 | <a class="ArticleLayoutHeader__info__doi" href="https://doi.org/10.3389/feart.2022.1032597">https://doi.org/10.3389/feart.2022.1032597</a>
The Upper Ordovician Wufeng to Lower Silurian Longmaxi Formation has a good material basis for marine shale gas development
and the structural preservation condition is the key factor to control the rich and integrated shale gas reservoirs in the Wuxi area of Chongqing City
Based on the seismic-structural interpretation data
combined with the regional structural background and drilling effect
the structural deformation characteristics and shale gas structural preservation conditions are comprehensively analyzed in the study area
The Wuxi area is located at the structural junction of the Sichuan Basin and southern Dabashan along with strong structural deformations
Seven rows of NW to near EW structural belts are mainly developed
The fold styles and fault development degrees of different structural belts are different
and the difference in the structural preservation conditions of shale gas is also obvious
The study results reveal that the shale gas structure preservation conditions of the Wufeng&#x02212;Longmaxi Formation in the Wuxi area are overall poor and only locally better
The structure preservation conditions for shale gas enrichment and accumulation are divided into four grades
the Heiloumen structural zone and Huangcaoping buried structural zone nearby the Sichuan Basin have good preservation conditions and are classified as the good Class I preservation area
The macroscopic preservation type of shale gas in the Wufeng&#x02212;Longmaxi Formation of the Wuxi area belongs to the complex structural preservation of the basin margin
Three structural preservation modes of shale gas in the study area have also been confirmed
The trap preservation type is more conducive to the preservation of shale gas
which is the most favorable structural mode for shale gas exploration
Although some shale gas exploration wells have achieved effective exploration results in this area
none of them is up to the commercial production scale
the complex geological structural conditions have an important impact on the accumulation and preservation of shale gas in the Wufeng&#x02212;Longmaxi Formation and deserve more attention
Due to the certain constraint of self-contained
a detailed evaluation of structural deformation characteristics may be conducted through the comprehensive analysis of shale gas enrichment
This study will systematically analyze the structural deformation characteristics and shale gas structural preservation conditions of the Wuxi area in Chongqing city based on the seismic-structural interpretation in the study area
combined with the regional tectonic background and actual drilling results
This may provide the geological basis for favorable shale gas exploration and development of the Upper Ordovician Wufeng to Lower Silurian Longmaxi Formation in the area
which is of great significance for us to understand shale gas accumulation and preservation in the complex structural belts at the margin of the Sichuan Basin
southern Dabashan linear synclinore&#x02212;epimetamorphic belt; &#x02160;2
northern Dabashan dome-shaped anticlinoria&#x02212;hypometamorphic belt; &#x02161;1
southern Dabashan imbricate fault belt; &#x02161;2
southern Dabashan ramp fold belt; &#x02161;3
southern Dabashan frontal fold belt; &#x02162;1
high-angle fold belt of eastern Sichuan Basin; &#x02163;1
A&#x02212;A&#x02032; seismic-structural profile in the study area
According to the interpretation results of seismic-structural data and regional structural distribution characteristics, taking the top boundary structures of Middle Ordovician as an example, the demonstration area can be divided into seven main NW to near EW structural belts from the north to south direction (<a href="#F3">Figures 3</a>, <a href="#F4">4</a>)
The detailed deformation characteristics of each structural belt are described as follows
Top boundary of Middle Ordovician in the study area
The Heiloumen structural belt locates at the southern margin of the study area with the NWW to near the EW strike and mainly develops a box-shaped anticline
Its southern and northern flanks are controlled by the Hei&#x02460; and Hei&#x02461; faults
which are distributed on the eastern and western sides of the structural belt
The western high point belongs to the box-shaped anticline with a relatively gentle form and the Lower Triassic Jialingjiang Formation is exposed in the core of the anticline
The eastern high point is connected with the saddle of the Maiyanshan hidden structure
which is located in the southern part of the Hongyan syncline
The structural form of this point is relatively wide and gentle
and the Middle Triassic Leikoupo Formation is exposed along the axis of the anticline
and the secondary faults are well developed
The Muziya structural belt lies between the Mu&#x02460; and Mu&#x02461; faults
which is a strip-like anticline with an NWW direction
Its whole structural form is steep in the south and gentle in the north and some secondary faults are developed along the axis of the anticline
The belt includes eastern and western structural high points
and the Lower to Middle Permian strata and Lower Triassic Jialingjiang Formations are exposed at the anticline core at the western and eastern high points
The Wenfeng structural belt distributes the hanging walls of Wen&#x02460; and Wen&#x02461; faults
which is classified as an NWW-trending strip-like anticline
The structural form is relatively stable as a whole steep in the south and gentle in the north
There are also some secondary faults in the axis zone of the anticline
The belt is divided into eastern and western high points
and its main high point is the Tianba anticline
The fluctuations of strata uplift and denudation in this belt are relatively large
so the exposed Lower Silurian Longmaxi shale formation is denuded and the oldest stratum on the surface is the Upper Cambrian
The Lower Triassic Feixianguan Formation is exposed at the core of the anticline in the eastern high point
The Huangcaoping hidden structural belt lies at the west-dipping end of the Wenfeng anticline, which is controlled by Wen&#x02460; and Gao&#x02461; faults, consisting of two rows of hidden high structural belts, namely, the southern and northern high structure zones (<a href="#F5">Figure 5</a>)
The general distribution of the two hidden zones is an NWW direction and its structural form has the characteristics of being relatively wide and gentle
Huangcaoping&#x02460; and Huangcaoping&#x02461; high points
The distribution of the northern hidden structural zone is very similar to that of the southern zone and there are also two high structural points
Huangcaoping&#x02462; and Huangcaoping&#x02463;
The belt is located at the structural transition zone and the extended distance and scale of the four high structural points are short and small
the buried depth of the two high structural points is superficial and the Lower to Middle Triassic strata are mainly exposed on the surface
B&#x02212;B&#x02032; seismic-structural profile in the study area
occurring on the hanging wall of the Yang&#x02460; fault and the footwall of the Wanyuan&#x02212;Wuxi fault
The two flanks of the anticline are very steep
and develop secondary overturned recumbent folds and faults
The entire structural belt is wide in the west and narrow in the east
and the Silurian is the oldest exposed strata in the core of the anticline
The Jiuchongshan structural belt locates the hanging wall of the Wanyuan&#x02212;Wuxi fault
which is also an NWW-trending anticlinorium along with strong compression and deformation
including fault bend fold and fault propagation fold
and most of their fold forms are closed and the formation occurrence changes repeatedly
mostly at high angles and locally reversed
The strata uplift and denudation in this belt are generally large and the local compression and fragmentation are also serious
The Upper Cambrian to Lower Triassic strata are exposed at the surface and the Wufeng&#x02212;Longmaxi Formation is broadly denuded in the middle part of the structural belt
The Zhongliangshan structural belt lies at the northeastern margin of the Wuxi area and is arranged parallel to the Jiuchongshan anticlinorium
The strata are often strongly deformed with generally developed secondary folds and faults
the surfaced and underground structures are obviously inconsistent and the fold form changes significantly in the deep underground
the Middle&#x02212;Lower Silurian to Lower Triassic strata are exposed along with severe compression and fragmentation and multiple high-angle fractures
there are poor gas-bearing shale target layers from the two cores
which are less than 0.5&#x000a0;m3/t and 0.8&#x000a0;m3/t of gas-bearing contents in the WQ2 and WQ1 wells
good external structural preservation conditions can play a critical role in the gas-bearing properties of black shale layers in addition to the shale itself having a good material basis for shale gas enrichment and accumulation
the quality of structural preservation conditions is the key factor controlling the enrichment and accumulation of shale gas in the Wuxi area
Development characteristics of organic micro-pores in the dark shale of the Wufeng&#x02212;Longmaxi Formation in the Wuxi area
X202 (1888.99&#x000a0;m); (B) black carbonaceous shale
X202 (1955.85&#x000a0;m); (C) gray black silty shale
X203 (3,616.64&#x000a0;m); (D) black carbonaceous shale
Connecting the well profile of shale target layers in the Wufeng&#x02212;Longmaxi Formation
Typical drilling core photographs of the Longmaxi Formation
and the red line direction is the stratum layer; (B) X203 well
and the fracture surface is filled with calcite veins; (C) WQ1 well
and the fracture surface is filled with calcite veins; (D) WQ1 well
with seriously broken strata and the core is broken into pieces; (E) WQ2 well
with high-angle strata and light sandy lamina; (F) WQ2 well
with a seriously crumpled and deformed strata
and the rock core is broken into pieces along the bedding plane
the structural condition is a major controlling factor for shale gas preservation
the evaluation of shale gas preservation depends on the combination methods of qualitative and quantitative analysis
Due to different regional tectonic backgrounds and differentiated degrees of research data
there is still no unified standard for the evaluation of shale gas preservation conditions
The Wuxi area is located in the basin-mountain coupling region and the macroscopic preservation type of shale gas is complex structural preservation of the basin margin
Through the detailed analysis of the structural conditions
the structural deformation is much stronger
so the structural preservation conditions are generally poor but are locally good and there are differentiated preservation conditions of shale gas in different regions
By the deformation characteristics of each structural belt, combined with the actual drilling effect of shale gas, the structural preservation conditions of shale gas in the Wufeng&#x02212;Longmaxi Formation can be evaluated in the area. Structure preservation conditions are divided into four grades, namely, the good Class I area, the general Class II area, the poor Class III area, and the very poor Class IV area (<a href="#F9">Figure 9</a>; <a href="#T1">Table 1</a>)
In the compound fold belt at the northern side of the Wanyuan&#x02212;Wuxi fault
the Jiuchongshan and Zhongliangshan structural belts have structural deformation
and both the surfaced and underground faults are well developed
The shale target layer of the Lower Silurian has extensive exposure and denudation
with high-angle fractures and very poor structural preservation condition of shale gas
and the western pinching end of the Muziya structural belt
the whole structural deformation is strong with relatively fragmented strata
mainly constructing anticlinoria and closed secondary folds
Faults are relatively well-developed with locally large faults
and the degree of formation uplift and denudation is rather large
The Permian to Lower Triassic strata are mainly exposed at the surface and the Lower Silurian is presented and denuded locally
The capping condition of the region is generally poor
In the Muziya structural belt and fold region at the southern side of the Wenfeng structural belt
which is mainly composed of asymmetric folds and open folds
There is a low development degree of faults in this region
with relatively well-developed high-angle fractures larger than 3&#x000a0;km from the surfaced large fault
the degree of formation uplift and denudation is rather small and the distance from the denudation zone of the shale target layer is more than 5&#x000a0;km
The Triassic strata are mainly exposed at the surface and partially exposed to the Lower Jurassic
The capping condition of the region in general belongs to the Class II area
In the Heiloumen structural region at the southern side of the Muziya structural belt and on the Huangcaoping hidden structure at the western pinching end of the Wenfeng structural belt
There is a relatively low development degree of faults in this region
larger than 5&#x000a0;km from the surfaced large fault
the degree of formation uplift and denudation is rather small and the distance from the denudation zone of the shale target layer is more than 10&#x000a0;km
The Upper Triassic to Middle&#x02212;Lower Jurassic strata are mainly exposed at the surface
and the capping condition of the region is good
Partitioning evaluation of structural preservation conditions of shale gas enrichment and accumulation in the Wufeng&#x02212;Longmaxi Formation
Grading evaluation of structural preservation conditions of shale gas enrichment and accumulation in the Wufeng&#x02212;Longmaxi Formation
Through the comprehensive analysis of the structural preservation conditions of shale gas enrichment and accumulation in the Wufeng&#x02212;Longmaxi Formation in the Wuxi area
the different structural preservation characteristics in different structural belts and their differences are very obvious
According to the differences in the structural styles and deformation intensity in the area
there are three structural preservation modes of shale gas enrichment and accumulation in the Wufeng&#x02212;Longmaxi Formation
Its specific characteristics are as follows
The lost destruction type focuses on the southern Dabashan ramp fault-fold belt with strong structural transformation. Intense structural compression deformation and formation uplift and denudation lead to complex fold changes in the Wuxi area, such as the development of faults and fractures, so that the formation capping condition becomes worse (<a href="#F10">Figure 10</a>)
The shale gas in the target layer of the Lower Silurian Longmaxi Formation has a large amount of it escape towards the superficial layers along the faulted fracture zones; especially the development of the enormous fault is directly connected with the surface
the surface is dominated by the Lower Silurian and even the target shale layer is denuded
The direct release of overlying pressure leads to the vertical loss of shale gas
resulting in a low enrichment degree of shale gas in the target layer and the destruction of effective shale gas accumulation
Structural preservation mode of shale gas enrichment and accumulation in the Wufeng&#x02212;Longmaxi Formation-lost destruction type
The lost residual type mainly develops on the southern Dabashan frontal fold belt with weak structural transformation. The surfaced faults and fractures are of the non-development type, and the Permian to Triassic strata are exposed, which have certain capping conditions, but the deformation of underground folds is very complex and thrust faults are well-developed in this belt (<a href="#F11">Figure 11</a>)
The shale gas escapes to the superficial layers along the structurally weak regions such as faulted fracture channels
the most of shale adsorbed gas is effectively preserved due to the unique compactness and adsorption of the black shale interval itself
Although good gas-bearing properties have been found in some drilling wells because of the massive loss of free gas
which gives rise to lower formation pressure and insufficient energy; it is difficult to achieve commercial production with the scale of adsorbed gas
the average gas content of the shale target layer in the X202 well is 2.07&#x000a0;m3/t
but the formation pressure coefficient is only 0.67 and no industrial gas flow is obtained
Structural preservation mode of shale gas enrichment and accumulation in the Wufeng&#x02212;Longmaxi Formation-lost residual type
The trap preservation type mainly manifests in the Heiloumen structural belt and Huangcaoping hidden structural belt near the interior of the Sichuan Basin with stable, wide, and gentle structural forms and the weak development of faulted fractures. The structural style in this region is dominated by wide-gentle fold and suspected box-shaped fold, and the Triassic to Jurassic strata are exposed at the surface with good capping conditions (<a href="#F12">Figure 12</a>)
The overlying capping layers in the two structural belts are rather thick
especially the Middle Triassic gypsum-salt rock layer has played a very good capping effect on the shale gas reservoir
Although there are also some faults developed in the deep underground
they are only developed in the Lower Triassic strata
so the loss of shale gas is very limited and the mode is more conducive to the enrichment
and preservation of shale gas in the high structural points
Structural preservation mode of shale gas enrichment and accumulation in the Wufeng&#x02212;Longmaxi Formation-trap preservation type
(1) The Wuxi area lies in the transition zone between the Dabashan thrust-fold belt and the Sichuan Basin
belonging to a superimposed transformation area with strong structural deformation
The area can be divided into seven structural belts
(2) The macroscopic preservation type of shale gas in the Wufeng&#x02212;Longmaxi Formation of the Wuxi area belongs to the complex structural preservation of the basin margin
The structural preservation conditions of shale gas enrichment and accumulation in the Wuxi area are divided into four grades
the Heiloumen structural zone and Huangcaoping buried structural zone near the Sichuan Basin have good preservation conditions and are classified as good Class I preservation areas
(3) Three structural preservation modes of shale gas in the Wuxi area have been identified, including lost destruction type, lost residual type, and trap preservation type. The trap preservation type is more conducive to the preservation of shale gas, which is the most favorable structural mode for shale gas exploration (<a href="#B22">Wang et al., 2006</a>; <a href="#B12">Liu and Wang, 2016</a>)
The original contributions presented in the study are included in the article/Supplementary Material; further inquiries can be directed to the corresponding author
The research was financially supported by the projects of the Chongqing Municipal Bureau of Planning and Natural Resources (KJ-2021026)
the Natural Science Foundation of Chongqing (cstc2021jcyj-msxmX0624 and CSTB2022NSCQ-MSX1221)
the Science and Technology Department of Sichuan Province (2021YFH0048)
and the project funded by the China Postdoctoral Science Foundation (2020M683253 and 2022T150774)
and ZZ were employed by Chongqing Shale Gas Exploration And Development Company Limited
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and implications of volcanic activity across the Ordovician&#x02013;Silurian transition in the Lower Yangtze region
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Mutual interference of layer plane and natural fracture in the failure behavior of shale and the mechanism investigation
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Keywords: structural deformation characteristics
Zhang Y and Liu J (2023) Structural deformation characteristics and its influence on shale gas preservation of the Wufeng&#x02212;Longmaxi Formation in the Wuxi area
Received: 31 August 2022; Accepted: 21 September 2022;Published: 09 January 2023
Copyright &#x000a9; 2023 Li, Luo, Yu, Tian, Sun, Wang, Wang, Zhong, Zhang and Liu. This is an open-access article distributed under the terms of the <a rel="license" href="http://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution License (CC BY).</a> The use
&#x0002a;Correspondence: Chuan Yu, <a id="encmail">eXVjaHVhbjAzMDQxNTEyQGFsaXl1bi5jb20=</a>
Volume 12 - 2024 | <a class="ArticleLayoutHeader__info__doi" href="https://doi.org/10.3389/feart.2024.1360202">https://doi.org/10.3389/feart.2024.1360202</a>
The marine shale within the Sichuan Basin constitutes China&#x02019;s significant shale gas production
there are significant differences in the shale gas preservation conditions and reservoir quality in different areas
limiting future large-scale exploration and development
Pore structure significantly influences shale reservoir quality
The influence of structural-dominated preservation conditions on shale pore structures is essential to comprehend for effective shale gas exploitation
This study employs field-emission scanning electron microscopy in conjunction with other techniques (low-temperature N2 adsorption
and nuclear magnetic resonance) for detailed analyses of the pore structure across varied structural zones
revealing the influence of structural attributes
and formation pressure on pore architecture
and examining the relationship between pore structure and shale gas preservation conditions
The results show that stable structural condition is conducive to the development and preservation of shale pores
Structural compression causes inorganic and organic pores to become narrow and elongated due to shrinkage
with a significant increase in microfractures
The porosity of shale with stable structural conditions exhibits markedly increased porosity compared to samples under structural compressions
Under conditions of similar TOC and mineral composition
and specific surface area (SSA) of shale after structural compression are significantly lower than those of samples with stable structural conditions
the shale porosity shows a decreasing trend
Burial depth significantly impacts the SSA and PV of high-TOC samples (3%&#x02013;6%)
both SSA and PV show a significant decreasing trend
The formation pressure coefficient is an important factor for the development and preservation of shale pores
and porosity is positively correlated with the formation pressure coefficient
Increased formation pressure coefficient indicates superior preservation conditions and enhanced pore development
which pose significant challenges for the next large-scale exploration and exploitation
The effect of structural preservation conditions on shale pore structure remain poorly understood compared to current understanding of nanoscale preservation conditions
Establishing the relationship between preservation conditions and pore structure has important scientific significance and exploration practical value for the study of shale gas preservation conditions and the evolution of shale pore structure
Field emission-Scanning electron microscopy (FE-SEM)
and nuclear magnetic resonance (NMR) have been widely used to illustrate pore structure parameters and their controlling factors
Based on comprehensive data of marine shale reservoir in Southern Sichuan Basin
these methods are employed in this study to (i) demonstrate the pore structure of the different structural area
(ii) reveal the effect of structure fault on pore structure
and (iii) quantitatively discuss the correlation between pore structure and structural preservation conditions of shale reservoir
Figure 1. (A) Paleogeography of Wufeng-Longmaxi Formation in Sichuan Basin. (B) Fault distribution and burial depth of Wufeng-Longmaxi Formation (modified from <a href="#B58">Zou et al., 2016a</a>; <a href="#B5">Dong et al., 2022</a>)
(C) Stratigraphic column of Wufeng-Longmaxi Formation in South Sichuan Basin
Based on core observation and outcrop observation
four shale samples of Wufeng-Longmaxi Formation shale samples obtained from coring wells and outcrop
These samples were processed into 25 mm &#x000d7; 25 mm core-plug sample for nuclear magnetic resonance (NMR) experiment
The remaining samples are for field emission-scanning electron microscope (FE-SEM) identification
low-temperature N2 (LTNA) and CO2 adsorption (LTCA) experiments and TOC measurement
Macroscopic characteristics of marine shale interval in Wufeng-Longmaxi Formation
(A) The maximum fracture width can reach 6 mm
(B) The degree of fracture development is significantly low
Well L206, at the core of the syncline, is distant from the significant fault, ensuring stable structural circumstances. Drilling core observations confirm absence of substantial fractures or notable structural compression features in the Wufeng-Longmaxi Formation (<a href="#F2">Figure 2B</a>). A limited number of tensile fractures emerge in specific depth intervals, maintaining a well-preserved shale with distinct bedding plane (<a href="#F3">Figure 3</a>)
Petrological characteristics of marine shale interval in Wufeng-Longmaxi Formation
and the TOC content is relatively low and close
The mineral composition is not significantly different
mainly composed of clay and siliceous minerals (quartz &#x0002b; feldspar)
with contents ranging from 47.53% to 50.14% and 41.84%&#x02013;43.14%
The content of carbonate rocks and pyrite is relatively low
with distribution ranges of 6.12%&#x02013;8.51% and 1.05%&#x02013;1.63%
Basic parameters of the marine shale samples under different structural conditions
The cross-plot of TOC content vs. porosity suggest that the shale porosity of Well L206 shows an increasing trend with the increase of TOC (<a href="#F4">Figure 4</a>)
2nd and 3rd Unit has the highest TOC content and highest porosity
the porosity range of Well H203 is between 1.5% and 5.0%
and does not show an increasing trend with the increase of TOC
The porosity of some samples from the Wufeng Formation and the 4th Unit showed a decreasing trend
significantly lower than that of shale samples with similar TOC content in Well L206
These shale samples are precisely distributed in the intervals with intense tectonic compression
it is suggested that strong tectonic compression can reduce the size of porosity
Comparison of shale porosity between the Wufeng-Longmaxi Formation of Well H 203 and Well L 206
FE-SEM images of nanoscale pores and fractures in Wufeng-Longmaxi Formation shale
(B) The pores at the edge of organic matter have directionality
(C) Fractures and oriented inorganic pores generated by compression
(D) A large number of inorganic pores with no directional distribution
(E) Non directional distribution of inorganic pores
Pore structure characteristics of Wufeng-Longmaxi Formation shale by LTNA and LTCA
According to the statistical results of specific surface area (SSA) and pore volume (PV), the SSA of No. 1 and No. 2 are 14.25 m2/g and 19.33 m2/g, respectively, and the PV is 7.58 &#x000d7; 10&#x02212;3 cm3/g and 8.87 &#x000d7; 10&#x02212;3 cm3/g. The SSA of No. 3 and No. 4 are 32.02 m2/g and 25.19 m2/g, respectively, and the PV is 17.08 &#x000d7; 10&#x02212;3 cm3/g and 18.07 &#x000d7; 10&#x02212;3 cm3/g (<a href="#T2">Table 2</a>)
2 are significantly lower than those of samples No
Pore structure parameters obtained by different experimental methods
shale samples that have not been compressed have more &#x0201c;relatively large pores,&#x0201d; or in other words
a larger proportion of &#x0201c;relatively large pores.&#x0201d; After structural compression
some of the &#x0201c;relatively large pores&#x0201d; in the shale are converted into &#x0201c;relatively small pores,&#x0201d; resulting in an increase in the proportion of &#x0201c;relatively small pores.&#x0201d;
NMR T2 spectra of shale samples saturated with low salinity brine
strong structural compression is not conducive to the development and preservation of pores
Structural compression is an important factor leading to a decrease in pore size and volume
In areas far away from structural compression and fault zones
with more and larger pores and higher porosity
which is conducive to shale gas enrichment
Burial depth and pressure coefficient of Wufeng-Longmaxi Formation in Sichuan Basin and surrounding areas
The relationship between shale porosity and burial depth in the Wufeng-Longmaxi Formation
(A) TOC value between 1% -2%; (B) TOC value between 2% -3%; (C) TOC value between 3% -4%; (D) TOC value between 4% -6%
This may be attributed to the weathering effect on the outcrop samples
Figure 9. The relationship between the specific surface area (SSA) and burial depth of shale in the Wufeng-Longmaxi Formation (Most of the data is cited from <a href="#B7">Fu, 2017</a>; <a href="#B37">Tang, 2018</a>; <a href="#B40">Wang, 2017</a>; <a href="#B41">Wang, 2021</a>; <a href="#B46">Yang, 2018</a>)
The increase in burial depth will amplify the compaction effect and inevitably enhance the destructive effect on pores
Despite factors such as high brittle mineral content and formation over-pressure that resist compaction
excessive burial depth is still a controlling factor for poor pore development
Figure 10. The relationship between the pore volume (PV) and burial depth of shale in the Wufeng-Longmaxi Formation (Most of the data is cited from <a href="#B7">Fu, 2017</a>; <a href="#B37">Tang, 2018</a>; <a href="#B40">Wang, 2017</a>; <a href="#B41">Wang, 2021</a>; <a href="#B46">Yang, 2018</a>)
Table 4. Classification scheme for formation pressure coefficient (<a href="#B8">Fu, 2016</a>; <a href="#B3">Chen et al., 2020</a>; <a href="#B20">Jin et al., 2023</a>)
Figure 11. Distribution characteristics of burial depth and pressure coefficient of shale formations in the Wufeng-Longmaxi Formation of the study area (modified from <a href="#B58">Zou et al., 2016a</a>; <a href="#B59">Zou et al., 2016b</a>; <a href="#B36">Tang et al., 2022</a>)
The relationship between the burial depth of the Wufeng-Longmaxi Formation and the formation pressure coefficient
Based on the influence of burial depth on pore structure parameters
it is speculated that this phenomenon is also applicable to shale pore structure
Coupling relationship between different burial depths
and shale porosity in the Wufeng-Longmaxi Formation
1) Stable structural conditions facilitate pore development and preservation in shale reservoir
Under the influence of structural compression
reducing inorganic and organic pores into narrowed and elongated forms with directional pore distribution and intensified micro-fracture evolution
Shale samples with stable structural conditions displays elevated porosity compared to compressed shale samples
Under similar TOC content and mineral composition
the pore size distribution curve of shale under structural compression shows significantly lower micropores and mesopores than other samples
The pore volume and specific surface area of shale under tectonic compression rank lower compared to others
The peak area on the right side of the T2 spectrum of saturated saline corresponds to the proportion of relative macropores and micro-fractures in the total pore volume
Shale samples subjected to structural compression exhibited significantly diminished pore volumes compared to other shale counterparts
implying substantial shrinkage in the volume of expanded pores and micro-fractures
shale reservoir porosity exhibits a declining pattern
Shale reservoir porosity with a burial depth of less than 3500 m ranges from 3% to 7%
while shale porosity with a burial depth of more than 3500 m ranges from 1% to 6%
Burial depth has a significant impact on the specific surface area and pore volume of high TOC shale (3%&#x02013;6%)
Burial depth causes a discernible decline in both specific surface area and pore volume
Upon reaching a shale burial depth of 4000 m
the distribution of pore volume and specific surface area data points becomes more concentrated
The pressure coefficient visualizes the shale pore development and preservation status
the better the preservation conditions of the shale reservoir
The pressure coefficient is positively correlated with porosity
High pressure coefficient can slow down the compaction effect of overlying strata
and moderate burial conditions play an important role in protecting the pores
The raw data supporting the conclusion of this article will be made available by the authors
The author(s) declare financial support was received for the research
This study was funded by the Innovation Consortium Project of China National Petroleum Corporation and Southwest Petroleum University (Grant No
and LH were employed by PetroChina Southwest Oil and Gasfield Company
The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest
The reviewer HL declared a shared affiliation with the author HT to the handling editor at the time of review
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Pore-structure characterisation of tectonically deformed shales: a case study of Wufeng-Longmaxi Formation in western Hunan Province
<a href="https://doi.org/10.1080/08120099.2019.1588168">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore-structure+characterisation+of+tectonically+deformed+shales:+a+case+study+of+Wufeng-Longmaxi+Formation+in+western+Hunan+Province,+southern+China&amp;btnG=">Google Scholar</a>
The shale gas enrichment factors of Longmaxi Formation under gradient basin-mountain boundary in South Sichuan Basin: tectono-depositional differentiation and discrepant evolution
<a href="https://doi.org/10.12017/dzkx.2021.005">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+shale+gas+enrichment+factors+of+Longmaxi+Formation+under+gradient+basin-mountain+boundary+in+South+Sichuan+Basin:+tectono-depositional+differentiation+and+discrepant+evolution&amp;btnG=">Google Scholar</a>
doi:10.13809/j.cnki.cn32-1825/te.2020.05.001
<a href="https://doi.org/10.13809/j.cnki.cn32-1825/te.2020.05.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Evolution+and+implications+of+shale+pore+structure+characteristics+under+different+preservation+conditions&amp;btnG=">Google Scholar</a>
Structural deformation characteristics and formation process of Luzhou block in Sichuan Basin
<a href="https://doi.org/10.3969/j.issn.1671-9727.2022.06.03">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Structural+deformation+characteristics+and+formation+process+of+Luzhou+block+in+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
Fault damage zone and its effect on deep shale gas: insights from 3D seismic interpretation in the southern Sichuan Basin
<a href="https://doi.org/10.1016/j.jsg.2023.104848">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fault+damage+zone+and+its+effect+on+deep+shale+gas:+insights+from+3D+seismic+interpretation+in+the+southern+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1306/07231212048">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Organic+matter-hosted+poresystem,+marcellus+formation+(devonian),+Pennsylvania&amp;btnG=">Google Scholar</a>
Pore types and pore-size distributions across thermal maturity
<a href="https://doi.org/10.1306/03051514151">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+types+and+pore-size+distributions+across+thermal+maturity,+Eagle+Ford+Formation,+southern+Texas&amp;btnG=">Google Scholar</a>
Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984)
<a href="https://doi.org/10.1351/pac198557040603">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Reporting+physisorption+data+for+gas/solid+systems+with+special+reference+to+the+determination+of+surface+area+and+porosity+(Recommendations+1984)&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.3787/j.issn.1000-0976.2015.05.003">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Comprehensive+evaluation+of+effective+preservation+zone+of+Longmaxi+Formation+shale+gas+in+the+Southeast+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Origin and evolution of overpressure in shale gas reservoirs of the upper ordovician Wufeng Formation-lower silurian Longmaxi Formation in the Sichuan Basin
<a href="https://doi.org/10.3787/j.issn.1000-0976.2022.10.004">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Origin+and+evolution+of+overpressure+in+shale+gas+reservoirs+of+the+upper+ordovician+Wufeng+Formation-lower+silurian+Longmaxi+Formation+in+the+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Tectonic control of shale gas accumulation in Longmaxi Formation in the southern Sichuan Basin
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Tectonic+control+of+shale+gas+accumulation+in+Longmaxi+Formation+in+the+southern+Sichuan+Basin.+%5Bdissertation%5D.+%5BXuzhou+(jiangsu+province)%5D&amp;btnG=">Google Scholar</a>
with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report)
<a href="https://doi.org/10.1515/pac-2014-1117">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Physisorption+of+gases,+with+special+reference+to+the+evaluation+of+surface+area+and+pore+size+distribution+(IUPAC+Technical+Report)&amp;btnG=">Google Scholar</a>
Stratigraphic framework of the Wufeng-Longmaxi shale in and around the Sichuan Basin
China: implications for targeting shale gas
<a href="https://doi.org/10.1016/j.engeos.2020.05.006">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Stratigraphic+framework+of+the+Wufeng-Longmaxi+shale+in+and+around+the+Sichuan+Basin,+China:+implications+for+targeting+shale+gas&amp;btnG=">Google Scholar</a>
The correlation between shale sealing capacity and the gas generation characteristics of shale organic matter
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+correlation+between+shale+sealing+capacity+and+the+gas+generation+characteristics+of+shale+organic+matter,+minerals+compositions+and+pore+structure&amp;btnG=">Google Scholar</a>
(2021).Study on shale gas accumulation process and enrichment mechanism of Wufeng-Longmaxi Formation in Changning Area
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Study+on+shale+gas+accumulation+process+and+enrichment+mechanism+of+Wufeng-Longmaxi+Formation+in+Changning+Area&amp;btnG=">Google Scholar</a>
Nanoscale pore characteristics of the lower permian shanxi formation transitional facies shale
<a href="https://doi.org/10.3389/feart.2022.842955">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Nanoscale+pore+characteristics+of+the+lower+permian+shanxi+formation+transitional+facies+shale,+eastern+ordos+basin,+North+China&amp;btnG=">Google Scholar</a>
Fluid activity and pressure evolution process of Wufeng-Longmaxi shales
<a href="https://doi.org/10.3799/dqkx.2021.049">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fluid+activity+and+pressure+evolution+process+of+Wufeng-Longmaxi+shales,+Southern+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Effect of faults on shale pore fracture and shale gas preservation: a case study of the Wufeng-Longmaxi Formation in the Northeast Yunnan Area
<a href="https://doi.org/10.1021/acs.energyfuels.2c01834">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Effect+of+faults+on+shale+pore+fracture+and+shale+gas+preservation:+a+case+study+of+the+Wufeng-Longmaxi+Formation+in+the+Northeast+Yunnan+Area&amp;btnG=">Google Scholar</a>
Main controlling factors of enrichment and high-yield of deep shale gas in the Luzhou Block
<a href="https://doi.org/10.3787/j.issn.1000-0976.2019.11.007">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Main+controlling+factors+of+enrichment+and+high-yield+of+deep+shale+gas+in+the+Luzhou+Block,+southern+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Pore structure and tracer-containing fluid migration in connected pores of Wufeng and Longmaxi shales from western Hubei and eastern Chongqing regions
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+structure+and+tracer-containing+fluid+migration+in+connected+pores+of+Wufeng+and+Longmaxi+shales+from+western+Hubei+and+eastern+Chongqing+regions.+%5Bdissertation%5D.+%5BWuhan+(Hubei+Province)%5D&amp;btnG=">Google Scholar</a>
Behavior of organic matter-hosted pores within shale gas reservoirs in response to differential tectonic deformation: potential mechanisms and innovative conceptual models
<a href="https://doi.org/10.1016/j.jngse.2022.104571">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Behavior+of+organic+matter-hosted+pores+within+shale+gas+reservoirs+in+response+to+differential+tectonic+deformation:+potential+mechanisms+and+innovative+conceptual+models&amp;btnG=">Google Scholar</a>
Experimental study on the existence of nano-scale pores and the evolution of organic matter in organic-rich shale
<a href="https://doi.org/10.1515/ntrev-2019-0015">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Experimental+study+on+the+existence+of+nano-scale+pores+and+the+evolution+of+organic+matter+in+organic-rich+shale&amp;btnG=">Google Scholar</a>
Natural fractures and their contribution to tight gas conglomerate reservoirs: a case study in the northwestern Sichuan Basin
<a href="https://doi.org/10.1016/j.petrol.2021.110028">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Natural+fractures+and+their+contribution+to+tight+gas+conglomerate+reservoirs:+a+case+study+in+the+northwestern+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
and prediction of natural fractures in deep tight sandstones of China
<a href="https://doi.org/10.1306/07052322120">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+review+of+the+genesis,+evolution,+and+prediction+of+natural+fractures+in+deep+tight+sandstones+of+China&amp;btnG=">Google Scholar</a>
Microstructure characterization of kerogen in mature shale: molecular investigation of micropore development
<a href="https://doi.org/10.1016/j.jngse.2021.104239">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Microstructure+characterization+of+kerogen+in+mature+shale:+molecular+investigation+of+micropore+development&amp;btnG=">Google Scholar</a>
Preservation mechanism and evaluation method of marine shale gas with complex tectonic background
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Preservation+mechanism+and+evaluation+method+of+marine+shale+gas+with+complex+tectonic+background&amp;btnG=">Google Scholar</a>
A novel pore size classification method of coals: investigation based on NMR relaxation
<a href="https://doi.org/10.1016/j.jngse.2020.103466">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+novel+pore+size+classification+method+of+coals:+investigation+based+on+NMR+relaxation&amp;btnG=">Google Scholar</a>
Predicting adsorbed gas capacity of deep shales under high temperature and pressure: experiments and modeling
<a href="https://doi.org/10.46690/ager.2022.06.05">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Predicting+adsorbed+gas+capacity+of+deep+shales+under+high+temperature+and+pressure:+experiments+and+modeling&amp;btnG=">Google Scholar</a>
Nanoscale pore characteristics of the jurassic dongyuemiao member lacustrine shale
<a href="https://doi.org/10.3389/feart.2022.1055541">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Nanoscale+pore+characteristics+of+the+jurassic+dongyuemiao+member+lacustrine+shale,+eastern+Sichuan+Basin,+SW+China:+insights+from+SEM,+NMR,+LTNA,+and+MICP+experiments&amp;btnG=">Google Scholar</a>
Evolution characteristics and models of shale pores and fractures under tectonic deformation: a case study of the Lower Paleozoic marine shale in the Sichuan Basin and its periphery
<a href="https://doi.org/10.11743/ogg20210116">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Evolution+characteristics+and+models+of+shale+pores+and+fractures+under+tectonic+deformation:+a+case+study+of+the+Lower+Paleozoic+marine+shale+in+the+Sichuan+Basin+and+its+periphery&amp;btnG=">Google Scholar</a>
Sequence stratigraphy and lithofacies paleogeographic evolution of katian stage-aeronian stage in southern Sichuan Basin
<a href="https://doi.org/10.1016/S1876-3804(21)60096-4">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Sequence+stratigraphy+and+lithofacies+paleogeographic+evolution+of+katian+stage-aeronian+stage+in+southern+Sichuan+Basin,+SW+China&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1016/s1876-3804(16)30022-2">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Shale+gas+in+China:+characteristics,+challenges+and+prospects+(II)&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.11698/PED.2015.06.01">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Shale+gas+in+China:+characteristics,+challenges+and+prospects+(Ⅰ)&amp;btnG=">Google Scholar</a>
Zhong K and He L (2024) The effect of structural preservation conditions on pore structure of marine shale reservoir: a case study of the Wufeng-Longmaxi Formation shale
Received: 22 December 2023; Accepted: 26 April 2024;Published: 15 May 2024
Copyright &#x000a9; 2024 Yu, Yuan, Tang, Luo, Wu, Liu, Yang, Zhong and He. This is an open-access article distributed under the terms of the <a rel="license" href="http://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution License (CC BY).</a> The use
&#x0002a;Correspondence: Weiming Yu, <a id="encmail">d29veXUwNzE3QDE2My5jb20=</a>
Volume 10 - 2022 | <a class="ArticleLayoutHeader__info__doi" href="https://doi.org/10.3389/feart.2022.809418">https://doi.org/10.3389/feart.2022.809418</a>
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A series of investigations have been conducted concerning the study of traditional stable isotopes and rare gas stable isotopes in natural gas
little is known regarding non-traditional stable isotopes of mercury in natural gas
especially in the development and utilization of shale gas in recent years
the presence of mercury in natural gas (including shale gas) provides a basis for research on mercury isotopes
Mercury was extracted from shale gas at the Wufeng-Longmaxi Formation in the YS108 block of the Zhaotong National shale gas demonstration area in the Sichuan Basin by using an acid potassium permanganate solution
followed by the analysis of mercury content and stable isotope composition
The mercury content in the marine shale gas at the Wufeng-Longmaxi Formation ranged from 171 to 2,906&#x000a0;ng/m3
with an average of 1,551.08 &#x000b1; 787.08&#x000a0;ng/m3 (n &#x0003d; 37
The &#x00394;199Hg values of mercury stable isotopes range from 02&#x02030; to 0.39&#x02030;
with an average of 22&#x02030; &#x000b1; 0.08&#x02030; (n &#x0003d; 37
1 SD); the &#x003b4;202Hg values range from &#x02212;1.68&#x02030; to &#x02212;0.04&#x02030;
with an average of &#x02212;0.87&#x02030; &#x000b1; 0.31&#x02030; (n &#x0003d; 37
which are significantly different from the &#x00394;199Hg and &#x003b4;202Hg information of coalbed gas
but similar to the &#x00394;199Hg and &#x003b4;202Hg information of terrestrial oil-type gas and the &#x00394;199Hg in the main hydrocarbon-forming organic matter of lower organisms such as algae (t-test
This indicates that terrestrial target strata with abundant algae or strata with positive &#x00394;199Hg are the target strata for the exploration of terrestrial oil and gas
As proposed by <a href="#B49">Ozerova (1983)</a>, the concentration of mercury (elemental mercury, Hg0) reflects the origin of natural gas. <a href="#B10">Dai (1992)</a> showed that Hg0 concentrations are greater than 700&#x000a0;ng/m3 in coalbed gas and less than 500&#x000a0;ng/m3 in oil-type gas. However, Hg0 concentrations vary significantly within a single gas field (<a href="#B38">Liu, 2013</a>)
the Hg0 concentration alone is an imprecise estimate of the natural gas source
stable isotopes of mercury in shale gas have not yet been reported
The development and utilization of shale gas help achieve the goals of &#x0201c;carbon peak&#x0201d; and &#x0201c;carbon neutrality,&#x0201d; which has become an important part of the energy structure of the world
The research object of this study is the existing shale gas in the Zhaotong Block of the Sichuan Basin
The mercury in shale gas was collected on-site
whereby we analyzed the mercury content and stable isotope composition of mercury in the samples
we compared the mercury stable isotope compositions of oil-type gas and coalbed gas in previous studies
the general characteristics of the mercury isotope composition of shale gas
and discussed the main material sources and exploration indicative significance of shale gas
FIGURE 1. Structural map of Zhaotong Demonstration Zone (A) and YS108 Block (B) [Figure A is modified according to <a href="#B72">Xu et al. (2019</a>), and Figure B is modified according to <a href="#B27">Huang et al. (2019</a>)]
and the horizontal wells of the related wells are drawn
The yellow and gray wells are other wells in the block
The mercury in the shale gas of seven gas accumulation wells from three gas accumulation platforms in Block YS108 of Zhaotong National Shale Gas Demonstration Zone in Sichuan Basin was collected on-site
A total of 37 samples of mercury capture fluid from shale gas were collected
we used three series of acid potassium permanganate cylinders to capture mercury in oil-type gas and coalbed gas
but laboratory simulations and mercury isotope tests found that Hg0 is mainly enriched in the first impinger (the percentage of mercury content is 76%&#x02013;97%)
and the isotopic composition of total mercury is consistent with that of the solution of the first impinger
we simplified the mercury capture device for shale gas
and the main body of the mercury capture device was composed of three impingers (Environmental Supply Company
500&#x000a0;ml for each sampling bottle) in series
The first impinger was an empty bottle for separating water vapor in shale gas
ensuring the concentration of acidic potassium permanganate mixture in the second impinger
The second impinger contained 100&#x000a0;ml of 4% (w/v) KMnO4 and 1% (v/v) H2SO4
Hg0 in shale gas was oxidized to ionic mercury and captured and retained in an acid potassium permanganate solution
The acid potassium permanganate solution was recovered as a sample for mercury content and mercury isotope analysis in shale gas
The third impinger contained approximately 100&#x000a0;mg of discolored silica gel
which was used to absorb the water vapor attached to the remaining gas to prevent its impact on the subsequent gas flowmeter
The three impingers were fixed in a cold-water tank
Mercury capture device for shale gas [Description: 1
Impact bottle with 4% (W/V) KMnO4&#x0002b;1% (V/V) H2SO4 solution; 4
Impact bottle with color-changing silicone; 5
To ensure the authenticity of mercury capture in shale gas
and their connecting tubes need to be processed in advance
which requires a low blank value of mercury
Potassium permanganate was purchased from the United States (mercury content is &#x0003c;0.002&#x000a0;ng/ml)
sulfuric acid is eminently pure (mercury content is &#x0003c;0.004&#x000a0;ng/ml)
and the impinger and its connecting parts are borosilicate glass bottles purchased from the United States and have been subjected to high-temperature treatment in a muffle furnace
The purchased PTFE pipe was used to connect the pipe from the shale gas wellhead to the impinger
the entire sampling device was directly flushed with the original natural gas of the shale gas wellhead for approximately 3&#x02013;5 min
and the acid potassium permanganate mercury-capturing mixture prepared on-site was quickly filled and connected to the whole device
Each sample captures 1 m3 of mercury in shale gas
which ensures the representativeness of the capture shale gas and enriches enough mercury to meet the requirements of mercury isotope analysis
the color of the mercury capture liquid should always be purple
the sampling should be immediately stopped
The acidic potassium permanganate mixture was recovered as the sample
and the volume of the mixture and gas flowmeter data were recorded
the mercury capture solution was recovered
and the volume was recorded with a measuring cylinder and transferred to a borosilicate glass bottle
Approximately 0.5&#x000a0;ml of potassium dichromate solution (30%
and transported back to the laboratory for testing
The mercury content of the captured mercury from acid potassium permanganate was determined by using the RA-915&#x000a0;M mercury meter and its liquid attachment
After the standard curve was plotted depicting the mercury standard solution
approximately 10&#x000a0;ml of acidic KMnO4 solution sample was added to the centrifuge tube
and then approximately 0.5&#x000a0;ml of NH2OH-HCl solution with a mass volume fraction of 15% was slowly added with a pipette
Shaking resulted in the captured mercury solution to be colorless and transparent
where 5&#x000a0;ml of the sample solution was added with a pipette to a 20% (w/v) SnCl2 solution foaming bottle open on the left side of the liquid attachment
Hg2&#x0002b; in the sample was reduced to Hg0 and was pumped by the instrument to the right foaming bottle containing 30% NaOH solution (the purpose was to remove the volatile acidic gas in the sample and prevent the host from being corroded)
Hg0 was sent to the host of the mercury analyzer to determine the mercury content
The sampling process was powered by a constant-speed gas pump in the liquid attachment
and the average value of each sample was taken as the final result after two measurements (relative deviation less than 10%)
where XXX refers to 199, 200, 201, 202, and 204, respectively. The mass-independent fractionation of mercury isotopes is represented by &#x00394;xxxHg (&#x02030;), which refers to the deviation between the measured and theoretical values. It is specifically calculated according to the following formula (<a href="#B4">Blum and Bergquist, 2007</a>):
The overall mercury content demonstrates coal-formed gas &#x0003e; oil-type gas &#x0003e; shale gas &#x0003e; coalbed gas
but the mercury content varies by one to several orders of magnitude
Mercury content in different types of natural gas
this study does not describe all geochemical processes that contribute to the mass fractionation of mercury isotopes
Characteristics of shale gas &#x00394;199Hg and &#x003b4;202Hg (A) and &#x00394;199Hg and &#x003b4; 201Hg (B): The ellipse in Figure A shows the mean values of &#x00394;199Hg and &#x003b4;202Hg (inner ellipse) and 95% confidence level (outer ellipse)
which also indicates that the mercury in shale gas undergoes the photoreduction reaction of Hg2&#x0002b; in water before deposition
There are relatively few studies on mercury isotopes in natural gas (<a href="#B62">Tang et al., 2019</a>; <a href="#B69">Washburn et al., 2018</a>), and the development and utilization of mercury isotopes in shale gas in recent years have not been reported. <a href="#F5">Figure 5</a> summarizes the results of shale gas and <a href="#B62">Tang et al. (2019)</a> on mercury isotopes in oil-type gas and coalbed gas
FIGURE 5. Comparison of mercury isotopic composition in different types of natural gas: the data of oil-type gas and coalbed gas are quoted from the literature (<a href="#B62">Tang et al., 2019</a>)
p &#x0003e; 0.05) and all values are positive
which also indicates that &#x00394;199Hg in marine crude oil is similar to that of algae
The &#x00394;199Hg of shale gas in the Zhaotong YS108 block, oil-type gas from the Liaohe oilfield, and Zhongyuan oilfield is significantly different from that of coalbed gas in mine no. 6 of the Hebi Coal Mine (<a href="#F5">Figure 5</a>). The coal seam in mine no. 6 of the Hebi coal mine is the continental coal seam of the Permian fluvial and lacustrine facies. The main coal-forming organic matter was terrestrial higher plants, and the &#x00394;199Hg was negative (<a href="#F6">Figure 6</a>)
the mercury &#x00394;199Hg (&#x02212;0.19&#x02030; to &#x02212;0.01&#x02030;
&#x02212;0.11&#x02030; &#x000b1; 0.06&#x02030;
&#x00394;199Hg is significantly different from that of shale gas and oil-type gas
The mercury content of marine shale gas in the YS108 block of Zhaotong demonstration area ranges from 171 to 2,906&#x000a0;ng/m3
with an average of 1,551.08 &#x000b1; 787.08&#x000a0;ng/m3 (n &#x0003d; 37,1 SD)
The &#x00394;199Hg values of mercury isotopes range from 0.02&#x02030; to 0.39&#x02030;
with an average of 0.22&#x02030; &#x000b1; 0.08&#x02030; (n &#x0003d; 37
and the &#x003b4;202Hg values range from &#x02212;1.68&#x02030; to &#x02212;0.04&#x02030;
which are significantly different from the &#x00394;199Hg and &#x003b4;202Hg values of coalbed gas
but not significantly different from the &#x00394;199Hg and &#x003b4;202Hg values of terrestrial oil-type gas
We can use it as an indicator to search for algae-rich continental strata or delineate the strata with positive &#x00394;199Hg as exploration targets
Further inquiries can be directed to the corresponding authors
ST: conceived the idea for this study and provided manuscript guidance; GZ: assisted in sample collection and manuscript revision; YD and ST: data analysis
All authors listed have made a contribution to the work and approved it for publication
This research was supported by the National Natural Science Foundation of China (41573006 and 41372360) and the CNPC (China National Petroleum Corporation) Scientific Research and Technology Development Project (Grant No
Author GZ was employed by the company PetroChina
We thank Gaoen Wu of State Key Laboratory of Environmental Geochemistry
We thank the editor and reviewers for their thoughtful comments
which significantly improved the quality of this paper
The Supplementary Material for this article can be found online at: <a href="https://www.frontiersin.org/articles/10.3389/feart.2022.809418/full#supplementary-material">https://www.frontiersin.org/articles/10.3389/feart.2022.809418/full&#x00023;supplementary-material</a>
Mass-Dependent and -Independent Fractionation of Hg Isotopes by Photoreduction in Aquatic Systems
<a href="https://pubmed.ncbi.nlm.nih.gov/17872409/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1126/science.1148050">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mass-Dependent+and+-Independent+Fractionation+of+Hg+Isotopes+by+Photoreduction+in+Aquatic+Systems&amp;btnG=">Google Scholar</a>
Natural Mercury Isotope Variation in Coal Deposits and Organic Soils
<a href="https://pubmed.ncbi.nlm.nih.gov/19068810/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es801444b">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Natural+Mercury+Isotope+Variation+in+Coal+Deposits+and+Organic+Soils&amp;btnG=">Google Scholar</a>
&#x0201c;Applications of Stable Mercury Isotopes to Biogeochemistry,&#x0201d; in Handbook of Environmental Isotope Geochemistry: Vol I
<a href="https://doi.org/10.1007/978-3-642-10637-8_12">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Applications+of+Stable+Mercury+Isotopes+to+Biogeochemistry&amp;btnG=">Google Scholar</a>
Reporting of Variations in the Natural Isotopic Composition of Mercury
<a href="https://pubmed.ncbi.nlm.nih.gov/17375289/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1007/s00216-007-1236-9">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Reporting+of+Variations+in+the+Natural+Isotopic+Composition+of+Mercury&amp;btnG=">Google Scholar</a>
Mercury Isotopes in Earth and Environmental Sciences
<a href="https://doi.org/10.1146/annurev-earth-050212-124107">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Isotopes+in+Earth+and+Environmental+Sciences&amp;btnG=">Google Scholar</a>
Magnetic Isotope Effect for Mercury Nuclei in Photolysis of Bis(p-Trifluoromethylbenzyl)mercury
<a href="https://doi.org/10.1134/S0012501607030013">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Magnetic+Isotope+Effect+for+Mercury+Nuclei+in+Photolysis+of+Bis(p-Trifluoromethylbenzyl)mercury&amp;btnG=">Google Scholar</a>
Odd Isotope Deficits in Atmospheric Hg Measured in Lichens
<a href="https://pubmed.ncbi.nlm.nih.gov/19731659/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es900578v">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Odd+Isotope+Deficits+in+Atmospheric+Hg+Measured+in+Lichens&amp;btnG=">Google Scholar</a>
Paleoenvironment and Mechanism of Organic&#x02010;Matter Enrichment in the Lower Silurian Longmaxi Formation Shale in the Sichuan Basin
<a href="https://doi.org/10.1111/1755-6724.13868">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geochemistry,+Paleoenvironment+and+Mechanism+of+Organic&#x02010;Matter+Enrichment+in+the+Lower+Silurian+Longmaxi+Formation+Shale+in+the+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
doi:10.1306/61EEDDBE-173E-11D7-8645000102C1865D
<a href="https://doi.org/10.1306/61EEDDBE-173E-11D7-8645000102C1865D">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fractured+Shale-Gas+Systems&amp;btnG=">Google Scholar</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Identification+of+Various+Alkane+Gases&amp;btnG=">Google Scholar</a>
Geochemistry of the Extremely High thermal Maturity Longmaxi Shale Gas
<a href="https://doi.org/10.1016/j.orggeochem.2014.01.018">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geochemistry+of+the+Extremely+High+thermal+Maturity+Longmaxi+Shale+Gas,+Southern+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Mercury Isotopes in a Forested Ecosystem: Implications for Air-Surface Exchange Dynamics and the Global Mercury Cycle
<a href="https://doi.org/10.1002/gbc.20021">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Isotopes+in+a+Forested+Ecosystem:+Implications+for+Air-Surface+Exchange+Dynamics+and+the+Global+Mercury+Cycle&amp;btnG=">Google Scholar</a>
Discussion on the Symbiotic Relationship between High Quality Source Rocks and Large Oilfields
<a href="https://doi.org/10.11935/j.issn.1673-1506.2019.05.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Discussion+on+the+Symbiotic+Relationship+between+High+Quality+Source+Rocks+and+Large+Oilfields&amp;btnG=">Google Scholar</a>
An Isotopic Record of Mercury in San Francisco Bay Sediment
<a href="https://doi.org/10.1016/j.chemgeo.2013.04.017">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=An+Isotopic+Record+of+Mercury+in+San+Francisco+Bay+Sediment&amp;btnG=">Google Scholar</a>
Holocene Atmospheric Mercury Levels Reconstructed from Peat Bog Mercury Stable Isotopes
<a href="https://pubmed.ncbi.nlm.nih.gov/28440654/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/acs.est.6b05804">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Holocene+Atmospheric+Mercury+Levels+Reconstructed+from+Peat+Bog+Mercury+Stable+Isotopes&amp;btnG=">Google Scholar</a>
Atmospheric Mercury Transfer to Peat Bogs Dominated by Gaseous Elemental Mercury Dry Deposition
<a href="https://pubmed.ncbi.nlm.nih.gov/26849121/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/acs.est.5b06058">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Atmospheric+Mercury+Transfer+to+Peat+Bogs+Dominated+by+Gaseous+Elemental+Mercury+Dry+Deposition&amp;btnG=">Google Scholar</a>
Mercury Isotope Fractionation during Liquid&#x02013;Vapor Evaporation Experiments
<a href="https://doi.org/10.1016/j.gca.2009.01.024">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Isotope+Fractionation+during+Liquid–Vapor+Evaporation+Experiments&amp;btnG=">Google Scholar</a>
Tracing Mercury Contamination Sources in Sediments Using Mercury Isotope Compositions
<a href="https://pubmed.ncbi.nlm.nih.gov/20387881/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es9039488">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Tracing+Mercury+Contamination+Sources+in+Sediments+Using+Mercury+Isotope+Compositions&amp;btnG=">Google Scholar</a>
&#x0201c;11.4 - Geochemistry of Mercury in the Environment,&#x0201d; in Treatise on Geochemistry
<a href="https://doi.org/10.1016/b978-0-08-095975-7.00904-9">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=11.4+-+Geochemistry+of+Mercury+in+the+Environment&amp;btnG=">Google Scholar</a>
Tracing Mercury Contamination from the Idrija Mining Region (Slovenia) to the Gulf of Trieste Using Hg Isotope Ratio Measurements
<a href="https://pubmed.ncbi.nlm.nih.gov/19209581/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es801772b">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Tracing+Mercury+Contamination+from+the+Idrija+Mining+Region+(Slovenia)+to+the+Gulf+of+Trieste+Using+Hg+Isotope+Ratio+Measurements&amp;btnG=">Google Scholar</a>
Variations in Stable Isotope Fractionation of Hg in Food Webs of Arctic Lakes
<a href="https://pubmed.ncbi.nlm.nih.gov/20000504/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es901771r">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Variations+in+Stable+Isotope+Fractionation+of+Hg+in+Food+Webs+of+Arctic+Lakes&amp;btnG=">Google Scholar</a>
The Geochemical Behavior and Isotopic Composition of Hg in a Mid-pleistocene Western Mediterranean Sapropel
<a href="https://doi.org/10.1016/j.gca.2008.12.012">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+Geochemical+Behavior+and+Isotopic+Composition+of+Hg+in+a+Mid-pleistocene+Western+Mediterranean+Sapropel&amp;btnG=">Google Scholar</a>
Mercury Spikes Suggest Volcanic Driver of the Ordovician-Silurian Mass Extinction
<a href="https://pubmed.ncbi.nlm.nih.gov/28706302/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1038/s41598-017-05524-5">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Spikes+Suggest+Volcanic+Driver+of+the+Ordovician-Silurian+Mass+Extinction&amp;btnG=">Google Scholar</a>
Basic Geological and Geochemical Characteristics of Unconventional Natural Gas Resources in China
<a href="https://doi.org/10.3724/SP.J.1140.2014.05095">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Basic+Geological+and+Geochemical+Characteristics+of+Unconventional+Natural+Gas+Resources+in+China.+Mar&amp;btnG=">Google Scholar</a>
Content Distribution Characteristics and Genetic Analysis of Mercury in the Natural Gas from Sichuan Basin
<a href="https://doi.org/10.11764/j.issn.1672-1926.2020.11.014">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Content+Distribution+Characteristics+and+Genetic+Analysis+of+Mercury+in+the+Natural+Gas+from+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Metal-organic Associations in Sediments&#x02014;I
Comparison of Unpolluted Recent and Ancient Sediments and Sediments Affected by Anthropogenic Pollution
<a href="https://doi.org/10.1016/0883-2927(90)90023-X">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Metal-organic+Associations+in+Sediments—I.+Comparison+of+Unpolluted+Recent+and+Ancient+Sediments+and+Sediments+Affected+by+Anthropogenic+Pollution&amp;btnG=">Google Scholar</a>
Discussion on Development Mode of Smaller Well Spacing and Tridimensional Development in the YS108 Block
Zhaotong National Shale Gas Demonstration Area
<a href="https://doi.org/10.11764/ji.ssn1672-1926.2018.12.018">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Discussion+on+Development+Mode+of+Smaller+Well+Spacing+and+Tridimensional+Development+in+the+YS108+Block,+Zhaotong+National+Shale+Gas+Demonstration+Area&amp;btnG=">Google Scholar</a>
Solution Speciation Controls Mercury Isotope Fractionation of Hg(II) Sorption to Goethite
<a href="https://pubmed.ncbi.nlm.nih.gov/22612062/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es3008112">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Solution+Speciation+Controls+Mercury+Isotope+Fractionation+of+Hg(II)+Sorption+to+Goethite&amp;btnG=">Google Scholar</a>
Photomicrobial Visible Light-Induced Magnetic Mass Independent Fractionation of Mercury in a Marine Microalga
<a href="https://doi.org/10.1021/acsearthspacechem.7b00056">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Photomicrobial+Visible+Light-Induced+Magnetic+Mass+Independent+Fractionation+of+Mercury+in+a+Marine+Microalga&amp;btnG=">Google Scholar</a>
Mercury Stable Isotopes for Monitoring the Effectiveness of the Minamata Convention on Mercury
<a href="https://doi.org/10.1016/j.earscirev.2020.103111">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Stable+Isotopes+for+Monitoring+the+Effectiveness+of+the+Minamata+Convention+on+Mercury&amp;btnG=">Google Scholar</a>
Interactions between Mercury and Phytoplankton: Speciation
<a href="https://pubmed.ncbi.nlm.nih.gov/24127330/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1002/etc.2424">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Interactions+between+Mercury+and+Phytoplankton:+Speciation,+Bioavailability,+and+Internal+Handling&amp;btnG=">Google Scholar</a>
Mercury Isotopic Evidence for Multiple Mercury Sources in Coal from the Illinois Basin
<a href="https://pubmed.ncbi.nlm.nih.gov/21222443/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es102875n">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Isotopic+Evidence+for+Multiple+Mercury+Sources+in+Coal+from+the+Illinois+Basin&amp;btnG=">Google Scholar</a>
Genesis of Mercury in Natural Gas of Chinese Gas Fields
<a href="https://doi.org/10.11764/j.issn.1672-1926.2012.03.413">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Genesis+of+Mercury+in+Natural+Gas+of+Chinese+Gas+Fields&amp;btnG=">Google Scholar</a>
Heavy Metal Uptake Capacities by the Common Freshwater green Alga Cladophora Fracta
<a href="https://doi.org/10.1007/s10811-011-9721-0">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Heavy+Metal+Uptake+Capacities+by+the+Common+Freshwater+green+Alga+Cladophora+Fracta&amp;btnG=">Google Scholar</a>
Occurrence Features and Gas Content Analysis of marine and continental Shales: A Comparative Study of Longmaxi Formation and Yanchang Formation
<a href="https://doi.org/10.1016/j.jngse.2018.06.019">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Occurrence+Features+and+Gas+Content+Analysis+of+marine+and+continental+Shales:+A+Comparative+Study+of+Longmaxi+Formation+and+Yanchang+Formation&amp;btnG=">Google Scholar</a>
(2020).Preliminary Study on Mercury Content and Mercury Isotopes in Coal-Derived Gas and Terrestrial Oil-type Gas in Xinjiang
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Preliminary+Study+on+Mercury+Content+and+Mercury+Isotopes+in+Coal-Derived+Gas+and+Terrestrial+Oil-type+Gas+in+Xinjiang&amp;btnG=">Google Scholar</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Petroleum+Geology&amp;btnG=">Google Scholar</a>
Mercury Concentration in Natural Gas and its Distribution in the Tarim Basin
<a href="https://doi.org/10.1007/s11430-013-4609-2">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Concentration+in+Natural+Gas+and+its+Distribution+in+the+Tarim+Basin&amp;btnG=">Google Scholar</a>
Source and Distribution of Mercury in Natural Gas of Major Petroliferous Basins in China
<a href="https://doi.org/10.1007/s11430-019-9596-6">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Source+and+Distribution+of+Mercury+in+Natural+Gas+of+Major+Petroliferous+Basins+in+China&amp;btnG=">Google Scholar</a>
Mercury Concentrations and Mercury Isotope Composition in lake Sediment Cores from the Vicinity of a Metal Smelting Facility in Flin Flon
<a href="https://doi.org/10.1016/j.chemgeo.2012.10.037">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Concentrations+and+Mercury+Isotope+Composition+in+lake+Sediment+Cores+from+the+Vicinity+of+a+Metal+Smelting+Facility+in+Flin+Flon,+Manitoba&amp;btnG=">Google Scholar</a>
Shale Gas Genesis and Carbon Isotope Inversion Mechanism of Wufeng Longmaxi Formation in Sichuan Basin -- Understanding from thermal Simulation experiment
<a href="https://doi.org/10.11781/sysydz202003428">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Shale+Gas+Genesis+and+Carbon+Isotope+Inversion+Mechanism+of+Wufeng+Longmaxi+Formation+in+Sichuan+Basin+--+Understanding+from+thermal+Simulation+experiment&amp;btnG=">Google Scholar</a>
Mercury Biogeochemical Cycling in the Ocean and Policy Implications
<a href="https://pubmed.ncbi.nlm.nih.gov/22559948/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1016/j.envres.2012.03.013">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Biogeochemical+Cycling+in+the+Ocean+and+Policy+Implications&amp;btnG=">Google Scholar</a>
north-central Texas: Gas-Shale Play with Multi&#x02013;Trillion Cubic Foot Potential
<a href="https://doi.org/10.1306/09170404042">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mississippian+Barnett+Shale,+Fort+Worth+basin,+north-central+Texas:+Gas-Shale+Play+with+Multi–Trillion+Cubic+Foot+Potential&amp;btnG=">Google Scholar</a>
Stable Carbon and Hydrogen Isotopic Characteristics of Natural Gas from Taibei Sag
<a href="https://doi.org/10.1016/S1876-3804(19)60033-9">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Stable+Carbon+and+Hydrogen+Isotopic+Characteristics+of+Natural+Gas+from+Taibei+Sag,+Turpan-Hami+Basin,+NW+China&amp;btnG=">Google Scholar</a>
Organic Matter Types of the Wufeng and Longmaxi Formations in the Sichuan Basin
South China: Implications for the Formation of Organic Matter Pores
<a href="https://doi.org/10.1021/acs.energyfuels.9b01453">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Organic+Matter+Types+of+the+Wufeng+and+Longmaxi+Formations+in+the+Sichuan+Basin,+South+China:+Implications+for+the+Formation+of+Organic+Matter+Pores&amp;btnG=">Google Scholar</a>
Sources of Mercury in Deep-Sea Sediments of the 481 Mediterranean Sea as Revealed by Mercury Stable Isotopes
<a href="https://pubmed.ncbi.nlm.nih.gov/31406135/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1038/s41598-019-48061-z">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Sources+of+Mercury+in+Deep-Sea+Sediments+of+the+481+Mediterranean+Sea+as+Revealed+by+Mercury+Stable+Isotopes&amp;btnG=">Google Scholar</a>
Evidence for Control of Mercury Accumulation Rates in Canadian High Arctic Lake Sediments by Variations of Aquatic Primary Productivity
<a href="https://pubmed.ncbi.nlm.nih.gov/17822088/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es070408x">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Evidence+for+Control+of+Mercury+Accumulation+Rates+in+Canadian+High+Arctic+Lake+Sediments+by+Variations+of+Aquatic+Primary+Productivity&amp;btnG=">Google Scholar</a>
Algal Scavenging of Mercury in Preindustrial Arctic Lakes
<a href="https://doi.org/10.1002/lno.11135">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Algal+Scavenging+of+Mercury+in+Preindustrial+Arctic+Lakes&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1080/00206818309466806">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=New+Mercury+Ore+belt+in+Western+Europe&amp;btnG=">Google Scholar</a>
First Discovery and Significance of Liquid Mercury in a Thermal Simulation Experiment on Humic Kerogen
<a href="https://doi.org/10.1021/acs.energyfuels.8b03294">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=First+Discovery+and+Significance+of+Liquid+Mercury+in+a+Thermal+Simulation+Experiment+on+Humic+Kerogen&amp;btnG=">Google Scholar</a>
Higher Mass-independent Isotope Fractionation of Methylmercury in the Pelagic Food Web of Lake Baikal (Russia)
<a href="https://pubmed.ncbi.nlm.nih.gov/22545798/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es204572g">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Higher+Mass-independent+Isotope+Fractionation+of+Methylmercury+in+the+Pelagic+Food+Web+of+Lake+Baikal+(Russia)&amp;btnG=">Google Scholar</a>
Role of Nuclear Volume in Driving Equilibrium Stable Isotope Fractionation of Mercury
<a href="https://doi.org/10.1016/j.gca.2007.02.004">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Role+of+Nuclear+Volume+in+Driving+Equilibrium+Stable+Isotope+Fractionation+of+Mercury,+Thallium,+and+Other+Very+Heavy+Elements&amp;btnG=">Google Scholar</a>
Mercury in marine Ordovician/Silurian Boundary Sections of South China Is Sulfide-Hosted and Non-volcanic in Origin
<a href="https://doi.org/10.1016/j.epsl.2019.01.028">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+in+marine+Ordovician/Silurian+Boundary+Sections+of+South+China+Is+Sulfide-Hosted+and+Non-volcanic+in+Origin&amp;btnG=">Google Scholar</a>
Mercury Stable Isotopes in Sediments and Largemouth Bass from Florida Lakes
<a href="https://pubmed.ncbi.nlm.nih.gov/23062970/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1016/j.scitotenv.2012.09.038">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Stable+Isotopes+in+Sediments+and+Largemouth+Bass+from+Florida+Lakes,+USA&amp;btnG=">Google Scholar</a>
High-precision Measurement of Mercury Isotope Ratios of Atmospheric Deposition over the Past 150 Years Recorded in a Peat Core Taken from Hongyuan
<a href="https://doi.org/10.1007/s11434-011-4396-0">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=High-precision+Measurement+of+Mercury+Isotope+Ratios+of+Atmospheric+Deposition+over+the+Past+150Years+Recorded+in+a+Peat+Core+Taken+from+Hongyuan,+Sichuan+Province,+China&amp;btnG=">Google Scholar</a>
Isotope Geochemistry of Mercury in Source Rocks
mineral Deposits and spring Deposits of the California Coast Ranges
<a href="https://doi.org/10.1016/j.epsl.2008.02.029">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Isotope+Geochemistry+of+Mercury+in+Source+Rocks,+mineral+Deposits+and+spring+Deposits+of+the+California+Coast+Ranges,+USA,+Earth+Planet&amp;btnG=">Google Scholar</a>
and Leachates of Mine-Waste Calcine from Areas Mined for Mercury
<a href="https://pubmed.ncbi.nlm.nih.gov/19848142/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es9006993">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Isotopic+Variability+of+Mercury+in+Ore,+Mine-Waste+Calcine,+and+Leachates+of+Mine-Waste+Calcine+from+Areas+Mined+for+Mercury&amp;btnG=">Google Scholar</a>
The Mercury Isotope Composition of Arctic Coastal Seawater
<a href="https://doi.org/10.1016/j.crte.2015.04.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+Mercury+Isotope+Composition+of+Arctic+Coastal+Seawater&amp;btnG=">Google Scholar</a>
Variations in the Isotopic Composition of Stable Mercury Isotopes in Typical Mangrove Plants of the Jiulong Estuary
<a href="https://pubmed.ncbi.nlm.nih.gov/27783251/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1007/s11356-016-7933-1">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Variations+in+the+Isotopic+Composition+of+Stable+Mercury+Isotopes+in+Typical+Mangrove+Plants+of+the+Jiulong+Estuary,+SE+China&amp;btnG=">Google Scholar</a>
Biogeochemical Controls on Mercury Stable Isotope Compositions of World Coal Deposits: A Review
<a href="https://doi.org/10.1016/j.earscirev.2015.11.005">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Biogeochemical+Controls+on+Mercury+Stable+Isotope+Compositions+of+World+Coal+Deposits:+A+Review&amp;btnG=">Google Scholar</a>
Stable Isotope Composition of Mercury Forms in Flue Gases from a Typical Coal-Fired Power Plant
<a href="https://doi.org/10.1016/j.jhazmat.2017.01.014">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Stable+Isotope+Composition+of+Mercury+Forms+in+Flue+Gases+from+a+Typical+Coal-Fired+Power+Plant,+Inner+Mongolia,+Northern+China&amp;btnG=">Google Scholar</a>
The Mercury Isotope Signatures of Coalbed Gas and Oil-type Gas: Implications for the Origins of the Gases
<a href="https://doi.org/10.1016/j.apgeochem.2019.104415">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+Mercury+Isotope+Signatures+of+Coalbed+Gas+and+Oil-type+Gas:+Implications+for+the+Origins+of+the+Gases&amp;btnG=">Google Scholar</a>
Mechanisms of Shale Gas Generation and Accumulation in the Ordovician Mechanisms of Shale Gas Generation and Accumulation in the Ordovician Wufeng-Longmaxi Formation
<a href="https://doi.org/10.1016/S1876-3804(17)30009-5">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mechanisms+of+Shale+Gas+Generation+and+Accumulation+in+the+Ordovician+Mechanisms+of+Shale+Gas+Generation+and+Accumulation+in+the+Ordovician+Wufeng-Longmaxi+Formation,+Sichuan+Basin,+SW+China&amp;btnG=">Google Scholar</a>
Heterogeneity of the Paleozoic Tight sandstone Reservoirs in Gaoqiao Area of Ordos Basin
<a href="https://doi.org/10.11743/ogg20140202">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Heterogeneity+of+the+Paleozoic+Tight+sandstone+Reservoirs+in+Gaoqiao+Area+of+Ordos+Basin&amp;btnG=">Google Scholar</a>
Sources and Transfers of Methylmercury in Adjacent River and forest Food Webs
<a href="https://pubmed.ncbi.nlm.nih.gov/23033864/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es3019836">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Sources+and+Transfers+of+Methylmercury+in+Adjacent+River+and+forest+Food+Webs&amp;btnG=">Google Scholar</a>
Mercury Biomagnification in Three Geothermally-Influenced Lakes Differing in Chemistry and Algal Biomass
<a href="https://pubmed.ncbi.nlm.nih.gov/24951892/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1016/j.scitotenv.2014.05.097">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Biomagnification+in+Three+Geothermally-Influenced+Lakes+Differing+in+Chemistry+and+Algal+Biomass&amp;btnG=">Google Scholar</a>
Using Mercury Isotopes to Understand Mercury Accumulation in the Montane Forest Floor of the Eastern Tibetan Plateau
<a href="https://pubmed.ncbi.nlm.nih.gov/27951639/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/acs.est.6b03806">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Using+Mercury+Isotopes+to+Understand+Mercury+Accumulation+in+the+Montane+Forest+Floor+of+the+Eastern+Tibetan+Plateau&amp;btnG=">Google Scholar</a>
Longmaxi Formation Shale Gas Geochemical Features Comparison between Different Blocks in Sichuan Basin
<a href="https://doi.org/10.1016/j.jngse.2015.11.045">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Longmaxi+Formation+Shale+Gas+Geochemical+Features+Comparison+between+Different+Blocks+in+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Isotopic Characterization of Mercury in Natural Gas via Analysis of Mercury Removal Unit Catalysts
<a href="https://doi.org/10.1021/acsearthspacechem.7b00118">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Isotopic+Characterization+of+Mercury+in+Natural+Gas+via+Analysis+of+Mercury+Removal+Unit+Catalysts&amp;btnG=">Google Scholar</a>
Equilibrium Mercury Isotope Fractionation between Dissolved Hg(II) Species and Thiol-Bound Hg
<a href="https://pubmed.ncbi.nlm.nih.gov/20443581/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/es100205t">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Equilibrium+Mercury+Isotope+Fractionation+between+Dissolved+Hg(II)+Species+and+Thiol-Bound+Hg&amp;btnG=">Google Scholar</a>
Geological Characteristics of Wufeng-Longmaxi Shale-Gas Reservoir in the Huangjinba Gas Field
<a href="https://doi.org/10.12029/gc20160120">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geological+Characteristics+of+Wufeng-Longmaxi+Shale-Gas+Reservoir+in+the+Huangjinba+Gas+Field,+Zhaotong+National+Shale+Gas+Demonstration+Area&amp;btnG=">Google Scholar</a>
Structural Deformation Characteristics and Shale Gas Preservation Conditions in the Zhaotong National Shale Gas Demonstration Area along the Southern Margin of the Sichuan Basin.china
<a href="https://doi.org/10.1016/j.ngib.2019.10.004">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Structural+Deformation+Characteristics+and+Shale+Gas+Preservation+Conditions+in+the+Zhaotong+National+Shale+Gas+Demonstration+Area+along+the+Southern+Margin+of+the+Sichuan+Basin.china&amp;btnG=">Google Scholar</a>
Mercury Isotope Variations between Bioavailable Mercury Fractions and Total Mercury in Mercury Contaminated Soil in Wanshan Mercury Mine
<a href="https://doi.org/10.1016/j.chemgeo.2012.04.017">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Isotope+Variations+between+Bioavailable+Mercury+Fractions+and+Total+Mercury+in+Mercury+Contaminated+Soil+in+Wanshan+Mercury+Mine,+SW+China&amp;btnG=">Google Scholar</a>
Mercury Stable Isotope Fractionation during Abiotic Dark Oxidation in the Presence of Thiols and Natural Organic Matter
<a href="https://pubmed.ncbi.nlm.nih.gov/30371069/">PubMed Abstract</a> &#x0007c; <a href="https://doi.org/10.1021/acs.est.8b05047">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Stable+Isotope+Fractionation+during+Abiotic+Dark+Oxidation+in+the+Presence+of+Thiols+and+Natural+Organic+Matter&amp;btnG=">Google Scholar</a>
Mercury Isotope Fractionation during Photoreduction in Natural Water Is Controlled by its Hg/DOC Ratio
<a href="https://doi.org/10.1016/j.gca.2009.08.016">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Isotope+Fractionation+during+Photoreduction+in+Natural+Water+Is+Controlled+by+its+Hg/DOC+Ratio&amp;btnG=">Google Scholar</a>
Nuclear Field Shift Effect in Isotope Fractionation of Mercury during Abiotic Reduction in the Absence of Light
<a href="https://doi.org/10.1021/jp910353y">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Nuclear+Field+Shift+Effect+in+Isotope+Fractionation+of+Mercury+during+Abiotic+Reduction+in+the+Absence+of+Light&amp;btnG=">Google Scholar</a>
Mercury Isotope Compositions across North American Forests
<a href="https://doi.org/10.1002/2015GB005323">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mercury+Isotope+Compositions+across+North+American+Forests&amp;btnG=">Google Scholar</a>
Zhang H and Li P (2022) Mercury Isotopes in Shale Gas From Wufeng-Longmaxi Shale Formation of Sichuan Basin
Southern China: A Preliminary Investigation
Received: 05 November 2021; Accepted: 17 January 2022;Published: 21 February 2022
Copyright &#x000a9; 2022 Tang, Ding, Zhu, Feng, Zhang and Li. This is an open-access article distributed under the terms of the <a rel="license" href="http://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution License (CC BY).</a> The use
&#x0002a;Correspondence: Shunlin Tang, <a id="encmail">dGFuZ3NodW5saW5AaHB1LmVkdS5jbg==</a>; Guangyou Zhu, <a id="encmail">emh1Z3Vhbmd5b3VAcGV0cm9jaGluYS5jb20uY24=</a>
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A consensus has been reached through previous studies that organic matter (OM) pores are crucial to porosity in many shale gas reservoirs; however
their origins and types remain controversial
we report the OM pore types hosted in algae
graptolite and other fossil fragments in the Wufeng-Longmaxi Formations of the Sichuan Basin
Algae types mainly include multicellular algae
The OM pores in multicellular algae usually exhibit irregular
and their diameters vary between 300 and 800 nm
The shapes of the OM pores in unicellular algae are either irregular or oval
and the pores are hundreds of nanometres in size
The pores associated with solid bitumen are sporadic
radiolarian and other fossil fragments are much smaller and fewer
The pores may only have developed in the surface of the graptolite and bitumen by filling in the biological cavity of the sponge spicule
These new findings provide stronger evidence that multicellular algae are the main hydrocarbon generating organisms of OM pores development
we identify and characterize OM types and OM pore types to gain key insights into the main factors controlling OM pore development in the Wufeng-Longmaxi Formations of the Jiaoshiba shale gas field in the Sichuan Basin
The OM pores in different types of OM (kerogen or hydrocarbon generating organisms
etc.) are different in both morphology and abundance
they have different effects on shale gas accumulation and production
The research results will be conducive to better understanding the OM pore network texture within shale
</a>Location map. Map of study area showing major shale gas fields and typical wells of the Wufeng-Longmaxi Formations in the Sichuan Basin and its surrounding areas.
</a>Stratigraphy maps. (a,b) a and b displaying the stratigraphy of the Upper Ordovician Wufeng Formation and lower Silurian Longmaxi Formation in wells Jiaoye 1 and Jiaoye 2, respectively; the locations of the two wells are shown in Fig. <a data-track="click" data-track-label="link" data-track-action="figure anchor" href="/articles/s41598-018-25104-5#Fig1">1</a>
Depths of the samples used for FE-SEM are also indicated
GR represents the results of the gamma ray (in American Petroleum Institute (API) units)
Under a scanning electron microscope (SEM)
OM is observed in the form of particulate debris
Most of the OM particles in the Wufeng-Longmaxi shale lack sharp edges and distinct shapes
Based on the morphology and inherited texture
the primary OM can comprise several hydrocarbon generating organisms
such as various algae (multicellular algae and unicellular algae
small organic domains or organoclay aggregates
Algae usually fill in the interparticle pores
which in many cases can be easily identified due to their sharp edges and distinctive internal fabric
The chemical compositions of algae are mainly carbon
which is created by the energy spectrum of algae and may contain a small amount of magnesium and sulphur
Algae such as multicellular algae and unicellular algae have been studied with great scrutiny in this area of research
</a>Multicellular algae of black shale in the Wufeng Formation in well Jiaoye 2 (2570.89 m)
(a) Overview of the profile displaying rich multicellular algae
The aligned OM pores may be a result of the inherent variation in the internal structure of the algae
and the aligned long and/or narrow OM pores may represent collapsed pores caused by compaction after hydrocarbon expulsion
(a) Rhabditiform blue algae colonies and OM pores (white arrows) observed in the Longmaxi Formation in well Jiaoye 2 (2523.11 m)
(b) Spherical bacteria colonies and OM pores (white arrows) of the Longmaxi Formation in well Jiaoye 1 (2380.45 m)
the small pores (white arrow) and the large pores (blue arrow) observed in the Longmaxi Formation in well Jiaoye 2 (2565.85 m)
The OM pores are developed by the arrangement gap (white arrow) and the algae were adrift (blue arrow)
The smallest pores developed on the bacteria can also be seen (red arrow)
(d) The energy spectrum of the rhabditiform blue algae is shown in (a)
(e) The energy spectrum of the spherical bacteria colonies is shown in (b)
The OM pores in multicellular algae are developed in the algae and inherit the original biological structure
The size of the pores is usually hundreds of nanometres
and sometimes the size can reach the micrometre level
The distribution pattern of pores is strongly affected by the arrangement gap between the unicellular algae and the pore sizes of tens to hundreds of nanometres
</a>Bitumen in the flocculent organic matter
(a,b) Bitumen fills the mineral interparticle pores of the Longmaxi Formation in well Jiaoye 2 (2543.84 m)
A micro-layer developed in the bitumen and is arranged in various directions
(c) Porous bitumen fills the framboidal pyrite of the Wufeng Formation in well Jiaoye 1 (2412.06 m)
(d) The energy spectrum and elements of the bitumen
</a>Pores in the solid bitumen of the Wufeng Formation in well Jiaoye 2 (2570.89 m)
(a) The honeycomb-like bitumen-hosted pores
while pores as large as several μm in diameter are also observed
Cracks are observed in the bitumen (white arrow)
(b) The honeycomb-like bitumen-hosted pores
Many OM grains in the Wufeng-Longmaxi shale are sharply defined straight or arcuate edges featuring a stratified distribution on the bedding surface
The appearance of these grains is consistent with the breakage fragments of graptolite
the graptolite (white arrows) is developed on the bedding surface of the Longmaxi Formation in well Jiaoye 1 (2380.45 m)
large pores (yellow arrows) and shrinkage joint between graptolite and minerals (blue arrows)
(c) Graptolite of the Wufeng Formation in well Jiaoye 1 (2415.19 m)
Shrinkage joint between graptolite and minerals (blue arrows)
(d) The energy spectrum of graptolite is shown in (b)
</a>Sponge spicule and the related pores of the Longmaxi Formation in well Jiaoye 2 (2556.91 m)
(b) The bitumen with pores in the sponge spicule (cross section) and pores within walls (blue arrow)
There are two major types of OM in the Wufeng-Longmaxi shale
including multiple hydrocarbon generating organisms and amorphous OM (bitumen)
which have been identified and analysed attentively in this study; this aids in determining how OM type impacts the type
Three distinct OM-hosted pore types were recognized in the Wufeng-Longmaxi shale
OM pores within interconnected OM (mainly multicellular algae) probably have better connectivity than that of the OM pores within spatially isolated particulate OM (mainly unicellular algae and/or bitumen)
The prediction of OM pores is mainly used to predict the content of retention crude oil and bitumen/migrated crude oil
Due to different mineral compositions of the different shale intervals
different degrees of compaction of mineral pores occur to the bitumen filling the mineral pores
The OM types and OM pore types highlighted in this paper provide a solid foundation for future studies
This study applies integrated two-dimensional (2D) field-emission scanning electron microscopy (FE-SEM) imaging and bulk analysis aiming to identify hydrocarbon generating organisms and further evaluate OM pores in siliciclastic-dominated and clay-dominated shale from the Wufeng-Longmaxi Formations of well Jiaoye 1 and well Jiaoye 2 in Jiaoshiba shale gas field of the Sichuan Basin
The combination of argon ion-polishing and scanning electron microscopy (SEM) enables the identification of nanopores in shale
the polished surface eliminates the spatial structure of the organic matter (inherited from kerogen)
which makes it indistinct to identify the OM type on the basis of SEM
As OM identification is a critical issue in this study
unpolished samples were used to retain the biological structure under SEM
mineral composition and scanning electron microscopy (SEM) experiments were conducted at the State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development
A Quanta 200 Environmental scanning electron microscope was used with image magnifications of between 10 and 20000
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Graptolite-derived organic matter in the Wufeng–Longmaxi Formations (Upper Ordovician–Lower Silurian) of southeastern Chongqing
China: Implications for gas shale evaluation
Formation of nanoporous pyrobitumen residues during maturation of the Barnett Shale (Fort Worth Basin)
Intact microbial fossils in the Permian Lucaogou Formation oil shale
Utilization of integrated correlative light and electron microscopy (iCLEM) for imaging sedimentary organic matter
Classification and the developmental regularity of organic-associated pores (OAP) through a comparative study of marine
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This project was supported by the National Natural Science Foundation of China (Grant No
Xu for their cordial assistance in the laboratory
State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development
Petroleum Exploration and Production Research Institute
China Petroleum &amp; Chemical Corporation (SINOPEC)
Sinopec Key Laboratory of Shale Oil/Gas Exploration and Production
All authors joined discussions for the final draft of the manuscript
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DOI: https://doi.org/10.1038/s41598-018-25104-5
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Volume 10 - 2022 | <a class="ArticleLayoutHeader__info__doi" href="https://doi.org/10.3389/feart.2022.879959">https://doi.org/10.3389/feart.2022.879959</a>
The Upper Ordovician&#x02013;Lower Silurian Wufeng&#x02013;Longmaxi (O3w-S1l) shale is widely distributed in the Xishui area
the potential and characteristics of shale gases in the Xishui area are not well evaluated
which has limited the exploration of shale gas in this area
we collected 14 fresh core samples of Wufeng&#x02013;Longmaxi Formations from Well XK-3 and conducted gas desorption experiments to evaluate the potential of shale gas resources in the Xishui area
After analyzing the chemical and isotopic composition of desorption gases
the origin and genesis of the shale gas were systematically studied
Our results show that the volume of desorption gases varies from 2.14&#x000a0;m3/t to 6.01&#x000a0;m3/t
showing great potential for shale gas in this area
The positive correlation between total organic carbon (TOC) and desorption gas volume indicates that organic matter provides the main pore volume for shale gas preservation
which are mainly composed of methane (99.64&#x02030;&#x02013;99.74%) with a very low content of ethane
the desorption gases are identified as oil-associated thermogenic gases
The carbon isotopic values of methane and ethane display reversal distribution
due to the mixing of primary gases from kerogen cracking and the secondary gases from retained oil cracking and further possible cracking of heavy gaseous hydrocarbons (C3H8&#x02014;C5H12) at higher thermal maturity (Ro &#x0003e; 2.00%)
the carbon isotopic values of shale gases of Wufeng&#x02013;Longmaxi shale also show different features at different areas
which are mainly controlled by the thermal maturity levels of the shale
the geochemical and isotopic characteristics of shale gas in this area are also not well studied
14 fresh core samples of Wufeng&#x02013;Longmaxi shale from Well XK-3
and chemical and isotopic composites of the desorption gases were analyzed
and the cause of carbon isotopic reversal were discussed after comparing with shale gas samples of Wufeng&#x02013;Longmaxi shale from other areas in the Sichuan Basin
The thickness of high-quality shale with a TOC value of more than 2.00% is about 20&#x000a0;m
in which the Wufeng Formation is around 5&#x000a0;m and the Guanyinqiao Member is only around 34&#x000a0;cm
FIGURE 1. Geological map of the Xishui area, north Guizhou, with the location of Well XK-3 (figure modified from <a href="#B26">Shi et al., 2019</a>)
The desorption gas was measured using specially designed equipment mainly composed of a sealed aluminum connected with a U-shaped glass tube
The fresh shale core samples were taken while drilling
and the saturated salt solution was filled into cans as quickly as possible
The desorption gas was released into a U-shaped glass tube
which is also filled with saturated salt solution
the desorption gas volume in a U-shaped glass tube can be measured using the labeled scale meter
The desorption gas volume (m3/t) at standard conditions can be calculated using the following equation:
where Vde is the desorption gas volume (m3/t) at standard conditions (P0 &#x0003d; 0.1&#x000a0;Mpa
V is the desorption gas volume in U-shaped glass tube and aluminum can
P is the pressure of the desorption gas in U-shaped glass
P0 is the standard atmospheric pressure (P0 &#x0003d; 0.1&#x000a0;Mpa)
The chemical composition of desorption gas samples was analyzed by Agilent 6890N GC equipped with a flame ionization detector and a thermal conductivity detector
Carbon isotopic (&#x003b4;13C) analysis of gases was analyzed using Isochrom GC-IRMS with the precision of &#x000b1;0.5&#x02030;
Hydrogen isotopic (&#x003b4;2H) analysis of gases was analyzed using IsoPrime GC-IRMS
Total organic carbon (TOC) was measured by using the LECO CS-800 analyzer
and the carbonates were removed by the hydrochloric acid (HCl) before measuring
The mineral compositions were analyzed using an Olympus X-ray Powder Diffraction (XRD) analyzer with CoK&#x003b1; radiation
and the powder was analyzed with a 2&#x003b8; value from 5&#x000b0; to 55&#x000b0;
TOC and mineral composition of 14 shale samples from Well XK-3
desorption gas volume (B) of 14 samples of Wufeng&#x02013;Longmaxi shale from Well XK-3
Gas volume and geochemical characteristics of desorption gases from Well XK-3
the &#x003b4;2H-CH4 (&#x02030;) values range from &#x02212;157.07&#x02030; to &#x02212;159.99&#x02030;
with a mean value of &#x02212;154.37&#x02030;
which is similar to Weiyuan (with a mean value of 141.50&#x02030;)
Jiaoshiba (with a mean value of 148.95&#x02030;)
and Changning (with a mean value of 148.00&#x02030;) areas
For discussing the origin of desorption gas, we also built the geological model of Well XK-3 by using PetroMod software with the constrain of measured maturity data (Ro%) from publications (<a href="#B41">Zhao et al., 2015</a>; <a href="#B11">Guo et al., 2016</a>). The results of burial and thermal histories of Wufeng&#x02013;Longmaxi shale from Well XK-3 are shown in <a href="#F5">Figure 5</a> (<a href="#B41">Zhao et al., 2015</a>; <a href="#B11">Guo et al., 2016</a>)
It can be seen that Wufeng&#x02013;Longmaxi shale of Well XK-3 experienced four stages of deep burial and uplift
The shale in Well XK-3 experienced a long-term erosion caused by Guangxi movement in the Late Silurian and the burial depth of Wufeng&#x02013;Longmaxi shale is shallow (&#x0003c;1,500&#x000a0;m)
when the temperature of Wufeng&#x02013;Longmaxi shale is about 70&#x000b0;C and the maturity (Ro%) of the shale is about 0.40%
there was short-term quick erosion due to the Dongwu movement (approximately 259&#x000a0;Ma)
the burial depth of Wufeng&#x02013;Longmaxi shale was also lower than 1,500&#x000a0;m
the temperature was approximately 90&#x000b0;C
the Wufeng&#x02013;Longmaxi shale of Well XK-3 entered into a long-term continuous deep burial stage and a short-term erosion related to the Indosinian movement occurred during the Late Triassic period
the temperature and maturity (Ro%) of Wufeng&#x02013;Longmaxi shale increased with the burial depth
Since the middle Triassic (approximately 235&#x000a0;Ma)
the Wufeng&#x02013;Longmaxi shale has been in the main oil stage (Ro &#x0003d; 0.70&#x02013;1.00%); the burial depth was more than 2,700&#x000a0;m
and the temperature was about 120&#x000b0;C
the shale entered into the wet gas stage at the Late Jurassic (Ro &#x0003e; 1.30%
approximately 150&#x000a0;Ma) and dry gas stage at the early stage of Late Cretaceous (Ro &#x0003e; 2.00%
The burial depth of Wufeng&#x02013;Longmaxi reached the maximum depth (approximately 5,500&#x000a0;m) at the Late Cretaceous
the temperature of the Wufeng&#x02013;Longmaxi shale in Well XK-3 reached 190&#x000b0;C
and the maturity of the shale reached the current level (around 2.21%)
the shale of Well XK-3 uplifted and was eroded because of the Himalayan movement
the burial depth of Wufeng&#x02013;Longmaxi shale in this area is about 650&#x000a0;m
Burial and thermal histories of Wufeng&#x02013;Longmaxi shale of Well XK-3 (A) and thermal model calibration (B)
we proposed that mixing gases from kerogen and retained oil cracking might be the main reason for the carbon isotopic reversal in this area
Generation history of hydrocarbons of Wufeng&#x02013;Longmaxi shale of Well XK-3
FIGURE 8. Plot of &#x003b4;13C-CH4 vs. &#x003b4;13C-C2H6 of shale gases of Longmaxi shale in different areas, Sichuan Basin. Data sources: (1) the Dingshan gas field (<a href="#B44">Zhong et al., 2019</a>); (2) the Weiyuan gas field (<a href="#B6">Dai et al., 2014</a>); (3) the Jiaoshiba gas field (<a href="#B5">Dai et al., 2016</a>; <a href="#B34">Yang et al., 2017</a>); and (4) the Changning gas field (<a href="#B5">Dai et al., 2016</a>; <a href="#B9">Feng et al., 2016</a>)
The current maturity (Ro%) values of Wufeng&#x02013;Longmaxi shale in Changning and Jiaoshiba areas are higher than those in Xishui
It may indicate that Wufeng&#x02013;Longmaxi shale in Changning areas experienced a longer period of heavier gases cracking into lighter gases
the carbon isotopic values of shale gases in Changning and Jiaoshiba are heavier than those of other areas
The gas desorption experiments on 14 fresh core samples of Wufeng&#x02013;Longmaxi Formations collected from Well XK-3 show the volume of desorption gases varies from 2.14&#x000a0;m3/t to 6.01&#x000a0;m3/t
suggesting great potential of shale gas resources for Wufeng&#x02013;Longmaxi shale in the Xishui area
Our results indicate that the shallow and thin shale still enjoys the high capability of gas resources
and Xishui anticlines is the most prospective exploration target for further exploration of shale gas
The positive relationship between desorption gas volume and TOC indicates that organic matter can provide more pore volume for shale gas storage
The desorption gases are typically dry gases
which are mainly composed of methane (99.64%&#x02013;99.74%)
with a little ethane (0.26%&#x02013;0.36%) and no detected nitrogen
The desorption gases are thermogenic origin and oil-associated gases
The carbon isotopic reversal is mainly caused by the mixing of gases from kerogen primary cracking and retained oil secondary cracking
The further cracking of heavy gaseous hydrocarbons during higher thermal maturity (Ro &#x0003e; 2.00%) may lead to the carbon isotopic differences of shale gases from Wufeng&#x02013;Longmaxi shale in different areas
The difference of geochemical and isotopic compositions in such a shallow thin shale layer is the maturation of the gases in comparison with deep thick shale layers in other areas
which should cause the attention for further studies and explorations
YW and HG presented the idea and conceived this study
and YW designed the field works and experiments
YW and HG interpreted the data and wrote the manuscript
This study was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA14010103
the National Natural Science Foundation of China (No
and the National Science and Technology Major Project of China (No
We also thank the editor and reviewers for their critical and constructive comments
which have improved this manuscript significantly
This is contribution No.IS-3156 from GIGCAS
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Significance of the Study on Carbon Isotopes of Alkane Gases
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Some Essential Geological and Geochemical Issues about Shale Gas Research in China
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Challenges and Prospects of Shale Gas Exploration in Wufeng-Longmaxi Reservoirs in the Sichuan Basin
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Geologic Structure Controls on Initial Productions of Lower Silurian Longmaxi Shale in south China
<a href="https://doi.org/10.1016/j.marpetgeo.2018.01.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geologic+Structure+Controls+on+Initial+Productions+of+Lower+Silurian+Longmaxi+Shale+in+south+China&amp;btnG=">Google Scholar</a>
Carbon Isotopic Composition of Shale Gas in the Silurian Longmaxi Formation of the Changning Area
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Hydrocarbon Generation and Shale Gas Accumulation in the Longmaxi Formation
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Geochemical and thermal Evolution of Wufeng-Longmaxi Shale and its prospect in the Xishui Area
<a href="https://doi.org/10.19700/j.0379-1726.2019.06.005">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geochemical+and+thermal+Evolution+of+Wufeng-Longmaxi+Shale+and+its+prospect+in+the+Xishui+Area,+North+Guizhou&amp;btnG=">Google Scholar</a>
Gas in Place and its Controlling Factors of the Shallow Longmaxi Shale in the Xishui Area
<a href="https://doi.org/10.1016/j.jngse.2020.103272">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Gas+in+Place+and+its+Controlling+Factors+of+the+Shallow+Longmaxi+Shale+in+the+Xishui+Area,+Guizhou,+China&amp;btnG=">Google Scholar</a>
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doi:10.1306/0c9b251f-1710-11d7-8645000102c1865d
<a href="https://doi.org/10.1306/0c9b251f-1710-11d7-8645000102c1865d">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Evaluation+of+a+Simple+Model+of+Vitrinite+Reflectance+Based+on+Chemical+Kinetics&amp;btnG=">Google Scholar</a>
Analysis and Thinking of the Difference of Wufeng-Longmaxi Shale Gas Enrichment Conditions between Dingshan and Jiaoshiba Areas in southeastern Sichuan Basin
<a href="https://doi.org/10.11764/j.issn.1672-1926.2020.02.011">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Analysis+and+Thinking+of+the+Difference+of+Wufeng-Longmaxi+Shale+Gas+Enrichment+Conditions+between+Dingshan+and+Jiaoshiba+Areas+in+southeastern+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Comprehensive Evaluation on Geological Conditions of the Shale Gas in Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in Dingshan Area
<a href="https://doi.org/10.16509/j.georeview.2017.01.014">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Comprehensive+Evaluation+on+Geological+Conditions+of+the+Shale+Gas+in+Upper+Ordovician+Wufeng+Formation-Lower+Silurian+Longmaxi+Formation+in+Dingshan+Area,+Qijiang,+Southeastern+Sichuan&amp;btnG=">Google Scholar</a>
Carbon and Hydrogen Isotope Systematics of Bacterial Formation and Oxidation of Methane
<a href="https://doi.org/10.1016/s0009-2541(99)00092-3">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Carbon+and+Hydrogen+Isotope+Systematics+of+Bacterial+Formation+and+Oxidation+of+Methane&amp;btnG=">Google Scholar</a>
Characterization of the Upper Ordovician and Lower Silurian Marine Shale in Northwestern Guizhou Province of the Upper Yangtze Block
South China: Implication for Shale Gas Potential
<a href="https://doi.org/10.1021/ef5004254">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characterization+of+the+Upper+Ordovician+and+Lower+Silurian+Marine+Shale+in+Northwestern+Guizhou+Province+of+the+Upper+Yangtze+Block,+South+China:+Implication+for+Shale+Gas+Potential&amp;btnG=">Google Scholar</a>
Isotopic Reversals with Respect to Maturity Trends Due to Mixing of Primary and Secondary Products in Source Rocks
<a href="https://doi.org/10.1016/j.chemgeo.2012.07.025">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Isotopic+Reversals+with+Respect+to+Maturity+Trends+Due+to+Mixing+of+Primary+and+Secondary+Products+in+Source+Rocks&amp;btnG=">Google Scholar</a>
Geochemical Characteristics and Origin of Natural Gas from Wufeng-Longmaxi Shales of the Fuling Gas Field
<a href="https://doi.org/10.1016/j.coal.2016.12.003">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geochemical+Characteristics+and+Origin+of+Natural+Gas+from+Wufeng-Longmaxi+Shales+of+the+Fuling+Gas+Field,+Sichuan+Basin+(China)&amp;btnG=">Google Scholar</a>
Assessing Shale Gas Resources of Wufeng-Longmaxi Shale (O3w-S1l) in Jiaoshiba Area
SE Sichuan (China) Using Petromod I: Burial and thermal Histories
<a href="https://doi.org/10.1080/10916466.2016.1176041">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Assessing+Shale+Gas+Resources+of+Wufeng-Longmaxi+Shale+(O3w-S1l)+in+Jiaoshiba+Area,+SE+Sichuan+(China)+Using+Petromod+I:+Burial+and+thermal+Histories&amp;btnG=">Google Scholar</a>
Characteristics and Distribution Pattern of Shale Gas Reservoir in Longmaxi Formation in Guizhou Province
<a href="https://doi.org/10.3969/j.issn.1001-1986.2015.03.005">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characteristics+and+Distribution+Pattern+of+Shale+Gas+Reservoir+in+Longmaxi+Formation+in+Guizhou+Province&amp;btnG=">Google Scholar</a>
Caledonian Erosion Thickness Reconstruction in the Sichuan Basin
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Caledonian+Erosion+Thickness+Reconstruction+in+the+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Characteristics and Gas Content Evaluation of Wufeng-Longmaxi Formation Shale in Well Xiye-1
doi:10.13776/j.cnki.resourcesindustries.20150514.012
<a href="https://doi.org/10.13776/j.cnki.resourcesindustries.20150514.012">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characteristics+and+Gas+Content+Evaluation+of+Wufeng-Longmaxi+Formation+Shale+in+Well+Xiye-1&amp;btnG=">Google Scholar</a>
Accumulation Conditions of Shale Gas from Lower Silurian Longmaxi Formation in Guizhou
<a href="https://doi.org/10.11817/j.issn.1672-7207.2016.09.024">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Accumulation+Conditions+of+Shale+Gas+from+Lower+Silurian+Longmaxi+Formation+in+Guizhou&amp;btnG=">Google Scholar</a>
Geological and Microstructural Characterization of the Wufeng-Longmaxi Shale in the Basin-Orogen Transitional Belt of North Guizhou Province
<a href="https://doi.org/10.1166/jnn.2017.14522">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geological+and+Microstructural+Characterization+of+the+Wufeng-Longmaxi+Shale+in+the+Basin-Orogen+Transitional+Belt+of+North+Guizhou+Province,+China&amp;btnG=">Google Scholar</a>
Characteristics of Lower Palaeozoic Hydrocarbon Source Strata and a Primary Study of the Shale Gas Accumulation in Northern Guizhou Province
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characteristics+of+Lower+Palaeozoic+Hydrocarbon+Source+Strata+and+a+Primary+Study+of+the+Shale+Gas+Accumulation+in+Northern+Guizhou+Province&amp;btnG=">Google Scholar</a>
Origin of Conventional and Shale Gas in Sinian-Lower Paleozoic Strata in the Sichuan Basin: Relayed Gas Generation from Liquid Hydrocarbon Cracking
<a href="https://doi.org/10.1306/11151817334">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Origin+of+Conventional+and+Shale+Gas+in+Sinian-Lower+Paleozoic+Strata+in+the+Sichuan+Basin:+Relayed+Gas+Generation+from+Liquid+Hydrocarbon+Cracking&amp;btnG=">Google Scholar</a>
Enrichment Conditions and Favorable Zone Prediction of Wufeng&#x02013;Longmaxi Shale Gas Reservoirs in the Northern Yunnan&#x02013;Guizhou Provinces
<a href="https://doi.org/10.3787/j.issn.1000-0976.2017.12.004">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Enrichment+Conditions+and+Favorable+Zone+Prediction+of+Wufeng–Longmaxi+Shale+Gas+Reservoirs+in+the+Northern+Yunnan–Guizhou+Provinces,+China&amp;btnG=">Google Scholar</a>
Geochemical Characteristics of Shale Gas and its Response to thermal Maturity (Ro) in the Longmaxi Formation
<a href="https://doi.org/10.1080/10916466.2018.1558241">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geochemical+Characteristics+of+Shale+Gas+and+its+Response+to+thermal+Maturity+(Ro)+in+the+Longmaxi+Formation,+Dingshan+Area,+Southeast+Sichuan&amp;btnG=">Google Scholar</a>
Shale Oil and Gas Revolution and its Impact
<a href="https://doi.org/10.7623/syxb202001001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Shale+Oil+and+Gas+Revolution+and+its+Impact&amp;btnG=">Google Scholar</a>
Isotopic Reversal (&#x00027;rollover&#x00027;) in Shale Gases Produced from the Mississippian Barnett and Fayetteville Formations
<a href="https://doi.org/10.1016/j.marpetgeo.2011.06.009">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Isotopic+Reversal+('rollover')+in+Shale+Gases+Produced+from+the+Mississippian+Barnett+and+Fayetteville+Formations&amp;btnG=">Google Scholar</a>
Keywords: Wufeng&#x02013;Longmaxi (O3w-S1l) shale
Sun Y and Guo H (2022) The Volume and Geochemical Characteristics of Desorption Gases From Wufeng&#x02013;Longmaxi (O3w-S1l) Shale in the Xishui Area
Received: 20 February 2022; Accepted: 07 March 2022;Published: 13 April 2022
Copyright &#x000a9; 2022 Shi, Wang, Sun and Guo. This is an open-access article distributed under the terms of the <a rel="license" href="http://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution License (CC BY).</a> The use
&#x0002a;Correspondence: Yunpeng Wang, <a id="encmail">d2FuZ3lwQGdpZy5hYy5jbg==</a>
Volume 11 - 2023 | <a class="ArticleLayoutHeader__info__doi" href="https://doi.org/10.3389/feart.2023.1119600">https://doi.org/10.3389/feart.2023.1119600</a>
attracting global exploration and development interest
China has abundant shale gas resources that will drive future oil and gas exploration advances by increasing reserves and production
The WY shale gas field is the most productive and has the greatest potential for exploration and development
This study analyzed high-quality shale logging response characteristics and drilling logging
and analytical test data in the WY area to establish a rock physical model of seismic attribute parameters and shale reservoir quality parameters
Seismic elastic parameters were converted into indicators that directly reflect shale reservoir quality
Corresponding regression equations were established to predict quality parameters.The results showed that shale reservoir quality parameters have a good correlation with seismic parameters
The TOC distribution ranged from 2% to 5% in the study area and was generally high in the north but low in the south
The high-quality shale reserve had a thickness of over 40 meters
The overall brittleness of the study area was favorable
which is suitable for network fractures formation in subsequent fracturing operations
The anisotropy of shale in S1l1I was small
and the overall fractures were underdeveloped in the study area
Drilling verifications showed that the prediction results of the quality parameters of high-quality shale reservoirs were consistent with actual drilling test results with high reliability
This study provides guidance for comprehensive prediction of sweet spots and subsequent fracturing and well location deployment.In summary
this study provides valuable insights into shale gas exploration and development in the WY area by establishing a rock physical model
and offering guidance for fracturing and well location deployment
To promote the large-scale production construction in this area and the increase in shale gas production in Southwest China
it remains crucial to evaluate the favorable exploration spots in this area
fracture prediction is also a major issue in shale gas exploration
research on the quality parameters of shale reservoirs is vital for predicting favorable zones
Previous studies on shale gas in the WY area have mainly focused on examining shale reservoir characteristics
while only a few have investigated the quality parameters of shale reservoirs
only a few researchers have comprehensively predicted sweet spots through the seismic prediction of shale reservoir quality parameters while restricting further developments to subsequent exploration and development work
To estimate shale reservoir quality parameters accurately
we selected the Longmaxi&#x02013;Wufeng Formation shale in the W204 well area as the research object in this study
The relationship between seismic elastic parameters and reservoir quality parameters was established by analyzing the shale reservoir&#x02019;s petrophysical properties in the work area through the analysis of high-quality shale logging response characteristics
The seismic data were converted into shale gas reservoir quality data
pre-stack fracture prediction was performed
providing a basis for evaluating shale gas area selection in the work area and guiding the subsequent fracturing construction and well site deployment
Structure location map of WY shale gas field
Comprehensive stratigraphic division table of WY area
According to the collected drilling logging data and the test analysis of core samples
we analyzed the high-quality shale logging response characteristics and conducted the rock physics analysis of organic carbon content
and other rock physics analyses of shale reservoirs
The relationship between seismic elastic parameters and reservoir quality parameters was established from the analysis of shale reservoir geological and logging response characteristics
combined with the rock physics analysis results
The post-stack inversion and pre-stack simultaneous inversion technology of constrained sparse pulse were used to convert the seismic data into shale gas reservoir quality parameters
Error statistics were then performed to illustrate the reliability of the method
Pre-stack anisotropic fracture prediction based on seismic data in the Offset-vector tiles (OVT) domain provides a basis for shale gas selection evaluation in the work area and guides subsequent well placement and fracturing operations
W204 is used as a drilling well for seismic inversion
W211 and W213 are used as wells for verification of seismic prediction results
The Longmaxi Formation&#x02013;Wufeng Formation shale reservoir in the WY area was systematically studied
and one well core (W204) was observed in detail
We selected 69 core samples from the Longmaxi&#x02013;Wufeng Formation shale section in the W204 well area for testing and analysis of total organic carbon (TOC)
six samples for testing and analysis of total gas content
and 62 samples for brittleness index testing
The collected three-dimensional work area was approximately 383.72&#x000a0;km2
Shale reservoir prediction was performed synthetically using the test
Through the intersection analysis of the quality and seismic parameters of the drilling shale reservoir in the W204 well area
we established various rock physical editions
such as the rock physical edition of the ratio of compressional and shear wave velocity and TOC
the ratio of brittleness index to compression and shear wave velocity
These rock physical editions provides a basis for subsequent predictions of reservoir quality parameters
Seismic inversion is a core technology for reservoir prediction (<a href="#B55">Zhou, 2015</a>)
We established the relationship between the seismic and evaluation parameters and proposed using Jason&#x02019;s constrained sparse pulse post-stack inversion and pre-stack simultaneous inversion to predict the quality parameters of shale gas reservoirs
These were based on the analysis of the geological characteristics and logging response characteristics of the Longmaxi&#x02013;Wufeng Formation shale in the WY area
combined with the analysis results of the rock physical characteristics of the reservoir
The thickness and porosity of shale reservoirs can be predicted through post-stack impedance inversion
pre-stack impedance inversion can be performed to obtain density
and brittleness index for TOC and brittleness prediction
pre-stack inversion can yield rich seismic elastic properties
which considerably increases the amount of information and number of methods for comprehensive geological and seismic interpretation
Seismic inversion section [(A) P-wave impedance inversion section
(C) P-S Wave Velocity ratio inversion section]
the pre-stack anisotropic fracture prediction based on the AVAZ was performed in the W204 well area using OVT gathers
The relevant data obtained can directly reflect vital information
such as reservoir fracture direction and density
which is helpful for drilling and developing oil wells
Statistical table of logging response characteristics of well W204
Logging curve characteristics and results of well W204
The organic carbon content is between 1.0% and 2.7%
with an average of 2.2%; the porosity is between 4.0% and 6.5%
with an average of 5.7%; the gas content varies greatly and is within 1.1&#x02013;3.3&#x000a0;m3/t; the brittleness index is between 40% and 45%
and the overall fracturing ability is relatively general
The organic carbon content is between 2.5% and 4.0%
with an average of 3.3%; the porosity is between 4.5% and 7.0%
with an average of 6.2%; the gas content is 2.5&#x02013;4.0&#x000a0;m3/t
with an average of 3.5&#x000a0;m3/t; the brittleness index is between 45% and 60%
and the overall fracturing ability is excellent
The organic carbon content is between 2.0% and 3.5%
with an average of 2.8%; the porosity is between 4.5% and 7.0%
with an average of 6.0%; the gas content is 2.5&#x02013;4.5&#x000a0;m3/t
with an average of 3.5&#x000a0;m3/t; the brittleness index is between 50% and 55%
and the overall fracturing ability is good
The organic carbon content is between 5.0% and 7.0%
with an average of 5.5%; the porosity is between 6.0% and 8.5%
with an average of 5.8%; the gas content is 4&#x02013;10&#x000a0;m3/t
with an average of 5.5&#x000a0;m3/t; the brittleness index is between 50% and 55%
and the overall fracturing ability is outstanding
The organic carbon content is between 1.0% and 2.5%; the porosity is between 2.0% and 5.0%
with an average of 4.0%; the gas content is 1.0&#x02013;4.5&#x000a0;m3/t
with an average of 2.0&#x000a0;m3/t; the brittleness index is generally between 45% and 50%
we developed a multiple regression model for organic matter
and velocity ratio of the longitudinal and shear waves
and Vp/Vs is the ratio of longitudinal to shear wave velocity [non-dimensional]
Cross plot of P-S wave velocity ratio and TOC
The absolute and relative errors of wells W204
The overall relative error did not exceed 10%
Shale reservoir quality parameters section [(A) TOC prediction section
Planar distribution map of shale TOC in the W204 well area (%)
Statistical table of average TOC seismic prediction errors of shale in the W204 well area
The relative error of the three wells was less than 9%
indicating that the prediction results are reliable
Planar distribution map of high-quality shale thickness in the W204 well area (m)
Statistical table of the prediction error of high-quality shale reservoir thickness
and the correlation with other parameters is average
Porosity can be predicted by the P-wave impedance data volume and density velocity volume obtained by seismic inversion
According to the above intersection relationship
we developed the following multiple regression model of porosity
and ZVP is longitudinal wave impedance [m/s &#x000b7; g/cm3]
Cross plot of P-wave impedance and porosity
the porosity prediction results are more reliable
Planar distribution of porosity in W204 well area
Statistical table of porosity prediction error of high-quality shale
a low ratio of compression to shear wave velocity and low density corresponds to a high brittleness index
we established a multiple regression model of the brittleness index
and ratio of longitudinal to shear wave velocities
and Vp/Vs is the ratio of longitudinal to shear wave velocities [non-dimensional]
Cross plot of brittleness index and P-S wave velocity ratio
Cross plot of brittleness index and density
and high brittle mineral content is the basis for natural fractures and fracturing in later developments
A rock structure with highly brittle minerals results in shale rock with a high Young&#x02019;s modulus and low Poisson&#x02019;s ratio
it is easy to form natural fractures and artificially induced fractures
which is advantageous for the migration and enrichment space of shale gas
it is important to estimate the brittleness index of shale gas reservoirs
and the relative error was 1.5%; the absolute error of the brittleness indexes of wells W211 and W213 were highly similar
and the relative errors were 8.8% and 7.8%
The relative errors of the three wells were less than 10%
indicating that the porosity prediction results were reliable
Planar distribution map of brittleness index in W204 well area
Statistical table of the prediction error of high-quality shale brittleness index
There are mainly two or more groups of cracks
among which the cracks in the near NS and near EW directions are the main ones
We performed the pre-stack anisotropic fracture prediction based on OVT data in the W204 well area
Rock core photos [(A) calcite full-filled high-angle fractures
2560&#x000a0;m (B) calcite full-filled multiple high-angle fractures
The analysis showed that the anisotropy in the study area was generally weak
and the fractures in the shale section of the Longyi 1 sub-member (S1l1I) were underdeveloped as a whole
Fractures were mainly developed in the EW and NS directions
and some were developed in the NW direction
Three groups of fractures were in the W204 well area
and one in the EW direction in the W213 well area
Three drilling locations of S1l1I fracture direction statistics in the W204 well area
(1) The TOC distribution range of the Longmaxi&#x02013;Wufeng Formation shale in the WY area was between 2% and 5%
with high TOC in the north and southeastern parts while low TOC is in the south
the overall thickness of high-quality reservoirs was more than 40&#x000a0;m
and the thickness distribution in local areas was between 30&#x000a0;m and 40&#x000a0;m
extending in the direction of the NE&#x02013;SW banding
(2) The porosity of the Longmaxi&#x02013;Wufeng Formation shale in the WY area changed slightly with a distribution range of 3%&#x02013;7%
almost all other areas had a porosity greater than 4%
The overall brittleness of the study area was relatively good
The brittleness index in most areas was greater than 35%
and the local brittleness index reached 65%
which is suitable for the formation of network fractures in subsequent fracturing operations
A comparison of the prediction results of this time with the drilling test data showed that the relative error was almost less than 10%
(3) The pre-stack anisotropic fracture prediction of AVAZ based on OVT data was performed in the WY area
The anisotropy in the study area was generally weak
The fractures in the shale of the Longyi 1 sub-member were underdeveloped as a whole
and the fracture development orientations were mainly east-west and north-south
followed by some fractures in the NW direction
and one group of fractures were developed in the W204
(4) This study comprehensively studied quality parameters sensitive to shale reservoir productivity
Seismic prediction of quality parameters was performed to provide a comprehensive prediction for sweet spots and subsequent wells
This work provides an important basis for bit deployment and fracturing
Compared with the uncertainty of previous single method or single reservoir quality parameter prediction
this study uses a variety of methods including pre-stack and post-stack to carry out comprehensive prediction of various reservoir quality parameters
which is more reliable and worthy of promotion
XH and WY contributed to the conception and design of the study
XH and WY wrote the first draft of this manuscript
CX and CY conducted the investigations and data collation
JL and BW reviewed and edited the manuscript
All authors contributed to the revision of the manuscript and read and approved the version submitted
This study was supported financially by the National Natural Science Foundation of China (Grant No
We would like to thank Chuanqing Drilling Engineering Co.
for providing data and allowing the publication of this article
Author WY was employed by the company CNPC Chuanqing Drilling Engineering Company Limited
Author CX was employed by the company Sinopec Northwest Oilfield Branch
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<a href="https://doi.org/10.19826/j.cnki.1009-3850.2020.12001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+study+on+the+enrichment+of+organic+materials+in+black+shales+of+the+Wufeng+to+Longmaxi+Formations+in+eastern+Sichuan+Basin&amp;btnG=">Google Scholar</a>
&#x0201c;Shale oil fracture prediction technology and application based on OVT seismic data,&#x0201d; in SPG/SEG Nanjing 2020 International Geophysical Conference Papers
<a href="https://doi.org/10.26914/c.cnkihy.2020.015057">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Shale+oil+fracture+prediction+technology+and+application+based+on+OVT+seismic+data&amp;btnG=">Google Scholar</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Genetic+conditions+of+the+shale+gas+and+delineation+of+the+favourable+areas+in+the+Wufeng+Formation-Longmaxi+Formation+on+the+southwestern+margin+of+the+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Comparison of constrained sparse spike and stochastic inversion for porosity prediction at Kristin Field
<a href="https://doi.org/10.1190/1.1438620">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Comparison+of+constrained+sparse+spike+and+stochastic+inversion+for+porosity+prediction+at+Kristin+Field&amp;btnG=">Google Scholar</a>
Reservoir and sweet pot distribution characteristics of shale gas in Wufeng-Longmaxi Formation,southwest of Sichuan Basin
<a href="https://doi.org/10.9901/j.fcgyq.2021.05.05">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Reservoir+and+sweet+pot+distribution+characteristics+of+shale+gas+in+Wufeng-Longmaxi+Formation,southwest+of+Sichuan+Basin&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1002/ente.201500464">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Shale+gas:+A+review+of+the+economic,+environmental,+and+social+sustainability&amp;btnG=">Google Scholar</a>
Progress in key technologies for evaluating marine shale gas development in China
<a href="https://doi.org/10.1016/s1876-3804(16)30120-3">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Progress+in+key+technologies+for+evaluating+marine+shale+gas+development+in+China&amp;btnG=">Google Scholar</a>
<a name="B16" id="B16"></a>Jiang, F. J., Pang, X. Q., and Ouyang, X. C. (2012). The main progress and problems of shale gas study and the potential prediction of shale gas exploration. Earth Sci. Front. 19 (02), 198&#x02013;211. Available at: <a href="https://kns.cnki.net/kcms/detail/detail.aspx?FileName=DXQY201202030&amp;DbName=CJFQ2012">https://kns.cnki.net/kcms/detail/detail.aspx?FileName&#x0003d;DXQY201202030&#x00026;DbName&#x0003d;CJFQ2012</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+main+progress+and+problems+of+shale+gas+study+and+the+potential+prediction+of+shale+gas+exploration&amp;btnG=">Google Scholar</a>
<a name="B17" id="B17"></a>Ladev&#x000e8;ze
Fault and natural fracture control on upward fluid migration: Insights from a shale gas play in the st
<a href="https://doi.org/10.1007/s10040-018-1856-5">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fault+and+natural+fracture+control+on+upward+fluid+migration:+Insights+from+a+shale+gas+play+in+the+st.+Lawrence+platform,+Canada&amp;btnG=">Google Scholar</a>
Research progress on evaluation methods and factors influencing shale brittleness: A review
<a href="https://doi.org/10.1016/j.egyr.2022.03.120">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Research+progress+on+evaluation+methods+and+factors+influencing+shale+brittleness:+A+review&amp;btnG=">Google Scholar</a>
Pore structure and fractal characteristics of the marine shale of the Longmaxi Formation in the changning area
<a href="https://doi.org/10.3389/feart.2022.1018274">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Pore+structure+and+fractal+characteristics+of+the+marine+shale+of+the+Longmaxi+Formation+in+the+changning+area,+southern+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
Effects of fracture formation stage on shale gas preservation conditions and enrichment in complex structural areas in the southern Sichuan Basin
<a href="https://doi.org/10.3389/feart.2022.921988">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Effects+of+fracture+formation+stage+on+shale+gas+preservation+conditions+and+enrichment+in+complex+structural+areas+in+the+southern+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
Geological characteristics of deep shale gas and their effects on shale fracability in the Wufeng&#x02013;Longmaxi Formations of the southern Sichuan Basin
<a href="https://doi.org/10.2113/1970/4936993">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geological+characteristics+of+deep+shale+gas+and+their+effects+on+shale+fracability+in+the+Wufeng–Longmaxi+Formations+of+the+southern+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
Impacts of shale gas advancements on natural gas utilization in the United States
<a href="https://doi.org/10.1002/ente.201402061">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Impacts+of+shale+gas+advancements+on+natural+gas+utilization+in+the+United+States&amp;btnG=">Google Scholar</a>
Anisotropy rock physics model for the Longmaxi shale gas reservoir
<a href="https://doi.org/10.1007/s11770-017-0609-x">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Anisotropy+rock+physics+model+for+the+Longmaxi+shale+gas+reservoir,+Sichuan+Basin,China&amp;btnG=">Google Scholar</a>
The progress and prospects of shale gas exploration and exploitation in southern Sichuan Basin
<a href="https://doi.org/10.11698/PED.2018.01.18">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+progress+and+prospects+of+shale+gas+exploration+and+exploitation+in+southern+Sichuan+Basin,+NW+China&amp;btnG=">Google Scholar</a>
China&#x02019;s shale gas exploration and development: Understanding and practice
<a href="https://doi.org/10.1016/s1876-3804(18)30065-x">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=China’s+shale+gas+exploration+and+development:+Understanding+and+practice&amp;btnG=">Google Scholar</a>
Geostatistical seismic rock physics AVA inversion with data-driven elastic properties update
<a href="https://doi.org/10.1109/TGRS.2021.3135718">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geostatistical+seismic+rock+physics+AVA+inversion+with+data-driven+elastic+properties+update&amp;btnG=">Google Scholar</a>
Relationship between sedimentary facies and shale gas geological conditions of the Lower Silurian Longmaxi Formation in southern Sichuan Basin and its adjacent areas
<a href="https://doi.org/10.7605/gdlxb.2016.03.032">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Relationship+between+sedimentary+facies+and+shale+gas+geological+conditions+of+the+Lower+Silurian+Longmaxi+Formation+in+southern+Sichuan+Basin+and+its+adjacent+areas&amp;btnG=">Google Scholar</a>
Sweet spot&#x0201d;comprehensive evaluation technology of complex mountain shale gas reservoir: Taking the Zhaotong National Shale Gas Demonstration Zone as an example
doi:10.11764/j.issn.1672-1926.2021.07.0012021
<a href="https://doi.org/10.11764/j.issn.1672-1926.2021.07.0012021">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Sweet+spotcomprehensive+evaluation+technology+of+complex+mountain+shale+gas+reservoir:+Taking+the+Zhaotong+National+Shale+Gas+Demonstration+Zone+as+an+example&amp;btnG=">Google Scholar</a>
Long interpretation methods for measuring the brittleness of tight reservoir
<a href="https://doi.org/10.16489/j.issn.1004-1338.2019.05.013">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Long+interpretation+methods+for+measuring+the+brittleness+of+tight+reservoir&amp;btnG=">Google Scholar</a>
<a name="B31" id="B31"></a>Sarkar, P., Singh, K. H., Ghosh, R., and Singh, T. N. (2018). Estimation of elastic parameters, mineralogy and pore characteristics of Gondwana shale in Eastern India for evaluation of shale gas potential. Curr. Sci. 115 (4), 710&#x02013;720. <a href="https://www.jstor.org/stable/26978280">https://www.jstor.org/stable/26978280</a>
<a href="https://doi.org/10.18520/cs/v115/i4/710-720">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Estimation+of+elastic+parameters,+mineralogy+and+pore+characteristics+of+Gondwana+shale+in+Eastern+India+for+evaluation+of+shale+gas+potential&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1016/j.jngse.2016.09.014">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=New+horizon+in+energy:+Shale+gas&amp;btnG=">Google Scholar</a>
<a name="B33" id="B33"></a>Shi, X. S., Liu, D. A., and Cui, Z. D. (2015). Analysis and thinking on fracturing technology of shale gas exploitation. Nat. gas Explor. Dev. 38 (03), 62&#x02013;65&#x0002b;69&#x0002b;12-13. Available at: <a href="https://kns.cnki.net/kcms/detail/detail.aspx?FileName=TRKT201503014&amp;DbName=CJFQ2015">https://kns.cnki.net/kcms/detail/detail.aspx?FileName&#x0003d;TRKT201503014&#x00026;DbName&#x0003d;CJFQ2015</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Analysis+and+thinking+on+fracturing+technology+of+shale+gas+exploitation&amp;btnG=">Google Scholar</a>
Quantitative paleogeographic mapping and sedimentary microfacies division in a deep-water marine shale shelf: Case study of wufeng-longmaxi shale
<a href="https://doi.org/10.14027/j.issn.1000-0550.2021.162">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Quantitative+paleogeographic+mapping+and+sedimentary+microfacies+division+in+a+deep-water+marine+shale+shelf:+Case+study+of+wufeng-longmaxi+shale,+southern+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
The successful development of gas and oil resources from shales in North America
<a href="https://doi.org/10.1016/j.petrol.2017.12.084">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+successful+development+of+gas+and+oil+resources+from+shales+in+North+America&amp;btnG=">Google Scholar</a>
Method of creationg common-offset/common azimuthe gathers in 3D seismic Survey and method of conducting Re&#x02043;flection attribute variation analysis
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Method+of+creationg+common-offset/common+azimuthe+gathers+in+3D+seismic+Survey+and+method+of+conducting+Re⁃flection+attribute+variation+analysis&amp;btnG=">Google Scholar</a>
Interpretation of the Penobscot 3D seismic volume using constrained sparse spike inversion
<a href="https://doi.org/10.1016/j.marpetgeo.2015.08.009">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Interpretation+of+the+Penobscot+3D+seismic+volume+using+constrained+sparse+spike+inversion,+Sable+sub-Basin,+offshore+Nova+Scotia&amp;btnG=">Google Scholar</a>
Analysis of distribution,storage potential land prospect for shale oil and gas in China
<a href="https://doi.org/10.6038/pg20130301">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Analysis+of+distribution,storage+potential+land+prospect+for+shale+oil+and+gas+in+China&amp;btnG=">Google Scholar</a>
Influences of adsorption/desorption of shale gas on the apparent properties of matrix pores
<a href="https://doi.org/10.1016/s1876-3804(16)30019-2">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Influences+of+adsorption/desorption+of+shale+gas+on+the+apparent+properties+of+matrix+pores&amp;btnG=">Google Scholar</a>
Integrating the latest achievements of scientific research and production
founding the first class platform of Petroleum geophysical exploration&#x02014;&#x02014;review of &#x00027; Petroleum geophysical exploration &#x00027; in 2014
doi:10.13810/j.cnki.issn.1000-7210.2015.04.027
<a href="https://doi.org/10.13810/j.cnki.issn.1000-7210.2015.04.027">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Integrating+the+latest+achievements+of+scientific+research+and+production,+founding+the+first+class+platform+of+Petroleum+geophysical+exploration——review+of+'+Petroleum+geophysical+exploration+'+in+2014&amp;btnG=">Google Scholar</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+main+controlling+factors+of+shale+gas+enrichment+and+exploration+prospect+areas+in+the+Sichuan-Yunnan-Guizhou+border+areas,+southwestern+China&amp;btnG=">Google Scholar</a>
Analysis on application effect of pre-stack fracture prediction using offset vector slice (OVT) technology in shale gas area
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Analysis+on+application+effect+of+pre-stack+fracture+prediction+using+offset+vector+slice+(OVT)+technology+in+shale+gas+area&amp;btnG=">Google Scholar</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Petroleum+geology&amp;btnG=">Google Scholar</a>
<a name="B44" id="B44"></a>Yan, Y. Q., Li, Y., Guo, S. H., Yang, X. X., and Hao, H. Y. (2021). Study and application of rock brittleness evaluation method based on compressive deformation characteristics. Xinjiang Oil Gas 17 (04), 21&#x02013;27. Available at: <a href="https://kns.cnki.net/kcms/detail/detail.aspx?FileName=XJSY202104005&amp;DbName=CJFQ2021">https://kns.cnki.net/kcms/detail/detail.aspx?FileName&#x0003d;XJSY202104005&#x00026;DbName&#x0003d;CJFQ2021</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Study+and+application+of+rock+brittleness+evaluation+method+based+on+compressive+deformation+characteristics&amp;btnG=">Google Scholar</a>
<a name="B45" id="B45"></a>Yang, Y. N., Wang, J., and Xiong, G. Q. (2016). Controls of sedimentary environments on shale gas reservoirs: A case study of the Wufeng and longmaxi formations in northeastern chongqing. Sediment. Geol. Tethyan Geol. 36 (03), 91&#x02013;97. Available at: <a href="https://kns.cnki.net/kcms/detail/detail.aspx?FileName=TTSD201603012&amp;DbName=CJFQ2016">https://kns.cnki.net/kcms/detail/detail.aspx?FileName&#x0003d;TTSD201603012&#x00026;DbName&#x0003d;CJFQ2016</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Controls+of+sedimentary+environments+on+shale+gas+reservoirs:+A+case+study+of+the+Wufeng+and+longmaxi+formations+in+northeastern+chongqing&amp;btnG=">Google Scholar</a>
Characteristics of Wufeng-Longmaxi For-mations shale sweet layer:Case study of Weiyuan-Rongchang block of SINOPEC
doi:10.11764/j.issn.1672&#x02014;1926.2019.04.006
<a href="https://doi.org/10.11764/j.issn.1672—1926.2019.04.006">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characteristics+of+Wufeng-Longmaxi+For-mations+shale+sweet+layer:Case+study+of+Weiyuan-Rongchang+block+of+SINOPEC&amp;btnG=">Google Scholar</a>
Application of constrained sparse pulse inversion technology in reservoir prediction of Xinmin Oilfield
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Application+of+constrained+sparse+pulse+inversion+technology+in+reservoir+prediction+of+Xinmin+Oilfield&amp;btnG=">Google Scholar</a>
Complex fracture development related to stratigraphic architecture: Challenges for structural deformation prediction
Tensleep Sandstone at the Alcova anticline
<a href="https://doi.org/10.1306/08040909110">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Complex+fracture+development+related+to+stratigraphic+architecture:+Challenges+for+structural+deformation+prediction,+Tensleep+Sandstone+at+the+Alcova+anticline,+Wyoming&amp;btnG=">Google Scholar</a>
Quantitative seismic prediction of shale gas sweet spots in lower silurian Longmaxi Formation
<a href="https://doi.org/10.11698/PED.2018.03.05">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Quantitative+seismic+prediction+of+shale+gas+sweet+spots+in+lower+silurian+Longmaxi+Formation,+weiyuan+area,+Sichuan+Basin,+SW+China&amp;btnG=">Google Scholar</a>
<a name="B50" id="B50"></a>Zhang, D. W. (2010). Strategic concepts of accelerating the survey &#x0201c;exploration and exploitation of shale gas resources in China&#x0201d;. Oil Gas Geol. 31 (02), 135&#x02013;139&#x0002b;150. Available at: <a href="https://kns.cnki.net/kcms/detail/detail.aspx?FileName=SYYT201002004&amp;DbName=CJFQ2010">https://kns.cnki.net/kcms/detail/detail.aspx?FileName&#x0003d;SYYT201002004&#x00026;DbName&#x0003d;CJFQ2010</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Strategic+concepts+of+accelerating+the+survey+exploration+and+exploitation+of+shale+gas+resources+in+China&amp;btnG=">Google Scholar</a>
History and key technological progress of natural gas development in the Sichuan Basin
<a href="https://doi.org/10.3787/j.issn.1000-0976.2021.12.007">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=History+and+key+technological+progress+of+natural+gas+development+in+the+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Application of constrained sparse spike inversion in the third member of Hetaoyuan Formation in Dupo Oilfield
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Application+of+constrained+sparse+spike+inversion+in+the+third+member+of+Hetaoyuan+Formation+in+Dupo+Oilfield&amp;btnG=">Google Scholar</a>
Micro-layers division and fine reservoirs contrast of Lower silurian longmaxi formation shale,Sichuan Basin,SW China
doi:10.11764/j.issn.1672-1926.2016.03.0470
<a href="https://doi.org/10.11764/j.issn.1672-1926.2016.03.0470">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Micro-layers+division+and+fine+reservoirs+contrast+of+Lower+silurian+longmaxi+formation+shale,Sichuan+Basin,SW+China&amp;btnG=">Google Scholar</a>
Logging evaluating methods of seven property parameters and enriched layers for Gulong shale oil reservoir in Songliao Basin
<a href="https://doi.org/10.19597/J.ISSN.1000-3754.202107003">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Logging+evaluating+methods+of+seven+property+parameters+and+enriched+layers+for+Gulong+shale+oil+reservoir+in+Songliao+Basin&amp;btnG=">Google Scholar</a>
The application of reservoir prediction technique in Fuyu reservoir of the central depression in Jilin oil field
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+application+of+reservoir+prediction+technique+in+Fuyu+reservoir+of+the+central+depression+in+Jilin+oil+field&amp;btnG=">Google Scholar</a>
A new method for evaluating favorable shale gas exploration areas based on multi-linear regression analysis: A case study of marine shales of wufeng-longmaxi formations
<a href="https://doi.org/10.19826/j.cnki.1009-3850.2021.05001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+new+method+for+evaluating+favorable+shale+gas+exploration+areas+based+on+multi-linear+regression+analysis:+A+case+study+of+marine+shales+of+wufeng-longmaxi+formations,+upper+Yangtze+region&amp;btnG=">Google Scholar</a>
Li J and Wang B (2023) Seismic prediction of shale reservoir quality parameters: A case study of the Longmaxi&#x02013;Wufeng formation in the WY area
Received: 09 December 2022; Accepted: 28 February 2023;Published: 28 March 2023
Copyright &#x000a9; 2023 Hu, Yu, Yi, Xiao, Li and Wang. This is an open-access article distributed under the terms of the <a rel="license" href="http://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution License (CC BY).</a> The use
&#x0002a;Correspondence: Wanli Yu, <a id="encmail">eXV3SV9zY0BjbnBjLmNvbS5jbg==</a>
For almost a century, Wu Feng (吳鳳) was known as a selfless, compassionate hero. Under both Japanese and Chinese Nationalist Party (KMT) rule, every child read in school about how Wu sacrificed himself to stop Aborigines from their “savage and backward headhunting practices.” 
Here’s the gist of the story: Wu spent much time with the Tsou Aborigines in what is today Chiayi County, teaching them how to farm and make crafts. After trying to delay their headhunting ritual to no avail, Wu told them to decapitate a man in red clothes who would pass by the next day. They did so, only to find that the man was Wu himself. Shocked and deeply saddened, the Aborigines vowed to give up the practice forever. 
Students today are likely oblivious to this figure, as on Sept. 12, 1989, Minister of Education Mao Kao-wen (毛高文) agreed to remove Wu’s story from the textbooks. 
It was a drastic fall. Four years earlier, the Wu Feng Temple (吳鳳廟) in Chiayi had held a grandiose celebration for the opening of Wu Feng Memorial Park to celebrate the 216th anniversary of Wu’s selfless act. The park soon lost its original name and became a cultural amusement park that went out of business in 2010. 
The commemorative 1985 book Wu Feng, The Righteous Man (義人吳鳳) contains songs, poems and submitted essays praising Wu’s character and his determination to “civilize our mountain compatriots.” There’s a curious disclaimer that the group of Tsou people who killed Wu no longer exist and have nothing to do with the modern Tsou. 
“The highest state of being for mankind is to selflessly help others. Wu Feng was able to [achieve this] because he understood love, he understood devotion, he understood bloodshed, he understood sacrifice and he understood death,” read one passage. 
Many of the essays attributed Wu’s upstanding morals to Chinese culture while demeaning the Aborigines as inferior people.
“Wu Feng was the first Han Chinese to give the mountain compatriots human rights. Throughout history, whenever Chinese culture came in contact with barbarians, it always used the method of gradual and natural assimilation. Wu Feng lived in savage lands but he did not let his superiority get the better of him. Instead, he did all he could to improve the lives of the mountain compatriots,” wrote schoolteacher Huang Kun-yuan (黃崑源). 
“The reason Han Chinese culture has been able to survive for thousands of years while absorbing weaker and inferior races is because of the Confucian virtues of compassion and righteousness,” wrote Yan Ming-hsiung (顏明雄), also a schoolteacher.
“Wu Feng sacrificed his life to change the bad habits of the Aborigines. This is because of the virtues that have been present in Chinese culture since ancient times ... We should carry forward the spirit of our people.” 
On a side note, almost every essay ended with something along the lines of “we must apply Wu Feng’s spirit to our lives so we can defeat the Communists and reclaim the mainland.” 
The first known account of Wu’s tale, published in 1855, was very different from the version found in the textbooks. It was a simple tale of how Wu volunteered to die for two Han Chinese villagers after asking them to flee. After his death, his ghost haunted the Aborigines and brought them great sickness. Terrified, the Aborigines vowed not to kill any more Han Chinese in that area and paid tribute to Wu’s grave every spring and fall. 
The story then becomes more elaborate. During the Japanese colonial era, Wu’s motives went from protecting his people to “civilizing the savages.” The purpose was manifold: to discourage Han Chinese from fighting against other races, to show that Aborigines can be civilized through kindness and also serve as an example for colonial officials. The tale was made into movies, plays and entered elementary school textbooks. 
The KMT adopted wholesale the Japanese version of the legend into its textbooks, promoting Wu as a beacon of Chinese virtues that people should look up to. 
But to Aborigines, it brought feelings of shame. 
“As a half Aborigine, I felt angry when I read this story. I was angry that I had the blood of such an uncivilized people in me,” writes Huang Hsiao-chiao (黃筱喬) in the study Sense of Identity Beginning from Wu Feng (身分認同從吳鳳說起). Others spoke in various reports of being looked down upon because of the story and even attacked by Han Chinese children who wanted to take revenge for Wu Feng. 
Wu’s downfall began in 1980, when anthropologist Chen Chi-nan (陳其南) wrote an article for the Minsheng Daily (民生報) titled A Fabricated Legend: Wu Feng (一個捏造的神話: 吳鳳). 
The Aboriginal rights movement soon took off, and during the 1985 ceremony, several Aborigines showed up wearing white shirts that read: “Wu is not a hero” and “Wu Feng’s story is the shame of education.” 
The rectification of Wu Feng’s story became a focus of Aboriginal protests, and in 1988, local pastor Lin Tsung-cheng (林宗正) led a group of Aborigines and destroyed the Wu Feng statue in front of Chiayi train station with a chainsaw. 
 At least one of Wu’s descendants, ninth-generation descendant Wu Liao-shan (吳廖善), didn’t seem to mind.
“It doesn’t really matter to me whether Wu Feng’s story remains in the textbooks or not,” Wu Liao-shan told the media. “The Aborigines say that the story causes people to look down on them, to bully them in school, so I guess it’s for the best to not include the story. But really, this is a problem with the teachers. They should teach their students not to bully others. Then we wouldn’t be facing this problem.”
Taiwan in Time, a column about Taiwan’s history that is published every Sunday, spotlights important or interesting events around the nation that have anniversaries this week.
Volume 9 - 2021 | <a class="ArticleLayoutHeader__info__doi" href="https://doi.org/10.3389/feart.2021.617831">https://doi.org/10.3389/feart.2021.617831</a>
This article is part of the Research TopicRock Physics and Geofluid Detection<a class="Link Link--linkType Link--maincolor Link--medium Link--icon Link--chevronRight Link--right" aria-label="View all 27 articles" href="https://www.frontiersin.org/research-topics/15166/rock-physics-and-geofluid-detection/articles" target="_self" data-event="customLink-linkType-a_viewAll27Articles">View all 27 articles</a>
This integrated study provides significant insight into parameters controlling the dynamic and static elastic behaviors of shale
Acoustic and geomechanical behaviors measurement from laboratory have been coupled with detailed petrographic and geochemical analyses
and microtexture observations on shale samples from the Wufeng&#x02212;Longmaxi Formation of the southeast Sichuan Basin
The major achievement is the establishment of the link between depositional environment and the subsequent microtexture development
which exerts a critical influence on the elastic properties of the shale samples
Microtexture and compositional variation between upper and lower sections of the Wufeng&#x02212;Longmaxi Formation show that the former undergoes normal mechanical and chemical compaction to form clay supported matrices with apparent heterogonous mechanical interfaces between rigid clasts and the aligned clay fabric
Samples from lower sections exhibited a microcrystalline quartz-supported matrix with a homogeneous mechanical interface arising from syn-depositional reprecipitation of biogenic quartz cement
This type of microtexture transition exerts primary control on elastic behavior of the shale samples
A clear &#x0201c;V&#x0201d; shaped trend observed from acoustic velocities and static Young&#x02019;s moduli document contrasting roles played by microtexture
porosity and organic matter in determining elastic properties
Samples with a quartz-supported matrix exhibit elastic deformation and splitting failure modes
The increment of the continuous biogenic quartz cemented medium with limited mechanic interface
samples showing a predominantly clay-supported matrix exhibited more signs of plastic deformation reflecting heterogeneous mechanical interfaces at grain boundaries
A better understanding of correlation between seismic parameters and causal mechanisms can help improve sweet-spot identification from seismic datasets
There is still a severe lack of mechanical understanding on how geomechancal behaviors are controlled by rock properties
and to what extend geomechancal properties can be inferred from seismic parameters
the relationships between reservoir quality
seismic and geomechanical rock properties and depositional environment and burial history
at scales relevant to exploration and production
are prerequisite to character &#x0201c;sweet-spots&#x0201d;
This paper describes a detailed rock physics study combined with microstructural analysis and diagenetic interpretation of core material from the Late Ordovician - Early Silurian Wufeng&#x02212;Longmaxi black shale of the southeast Sichuan Basin
petrophysical and microstructural properties of about 82 core samples
The objectives were 1) to identify relationships between velocity and rock composition and between TOC content and porosity
2) to interpret observed velocity anisotropy
3) to examine mechanical behavior and failure mode
4) to determine static Young&#x02019;s moduli and any mineral content dependence and 5) to evaluate the brittleness index
An integrated study of this sort provides significant insight into key factors controlling the acoustic and geomechanical behaviors of the Wufeng&#x02212;Longmaxi Formation shale
especially depositional and diagenetic controls on its macroscopic seismic and geomechanical properties (Hereafter
the Wufeng-Longmaxi Formation shale is referred to simply as the Longmaxi Formation for the sake of brevity.)
anoxic shelf environment hosting uniform deposition of several organic-rich shale horizons (Longmaxi Formation)
FIGURE 1. (A) Location and paleogeographic map of the study area in south Sichuan Basin, and the structural subdivisions include the east district, the south district, the north district, the central district the (modified from <a href="#B8">Chen et al. (2016)</a>, <a href="#B26">Hao et al. (2008)</a>)
(A) Sequence stratigraphic framework of Wufeng-Longmaxi Formation shale
ORSS: Organic-rich siliceous shale; ORMS: Organic-rich mixed shale; ORAS: Organic-lean argillaceous shale; OMSS: Organic-moderate siliceous shale; OMMS: Organic-moderate mixed shale; OMAS: Organic-moderate argillaceous shale
TST:transgressive systems tract; EHST: early highstand systems tract; LHST: late highstand systems tract (LHST); LST: low stand system tract; HST: highstand systems tract
(B) Relationship of TOC content and quartz content
(C) Relationship of TOC content and porosity
Data are sorted by sedimentary circumstance
Exact mineral compositions of the 82 samples were determined through powder XRD (X-ray diffraction) analysis and pyrolysis
This procedure analyzed crushed sample powders (grain sizes less than 48&#x000a0;&#x003bc;m) using a PANalytical (Empyrean) X-ray diffractometer
Whole rock geochemical analyses were conducted on 37 samples using inductively coupled plasma-mass spectrometry (ICP-MS)
These analytical methods yield data for 13 major oxides and 10 trace elements
Analytical results were calibrated with laboratory internal standards
Total organic content (TOC) was also measured for samples using standard high-temperature pyrolyzation methods and A Leco carbon/sulfur analyzer
This study used SEM and CL imaging to differentiate extrabasinal quartz and diagenetic quartz
which provided important clues concerning the Longmaxi Formation&#x02019;s depositional and diagenetic history
Ultrasonic transmission techniques were used to measure seismic velocity in dry samples
Measurements were conducted for various confining pressures at nominal center frequencies of 800&#x000a0;kHz for the P-wave transducer and 350&#x000a0;kHz for the S-wave transducer
Experiments began within a pressure cell at room temperature and confining pressures of 2&#x000a0;MPa
which ran up to 80&#x000a0;MPa in increments of 5&#x000a0;MPa
the first break of the transmitted pulse was selected from a 20&#x000a0;min period during which the sample strain fell below 2 &#x000d7; 10&#x02013;4
This technique gave velocity measurement precisions of about &#x000b1;1% for the compressional wave and about &#x000b1;2% for shear waves
Deviations in pressure were less than 0.3%
According to wave polarization and propagation directions with respect to bedding plane of core plugs
this method allowed measurement of six velocities
V SH-0&#x000b0;and VSV-0&#x000b0;for vertically propagating waves and VP-90&#x000b0;
VSV-90&#x000b0;and VSH-90&#x000b0;for horizontally propagating waves
where the subscript P represents the compressional wave
subscript SV indicates the polarization perpendicular to bedding and subscript SH indicates polarization parallel to bedding
These velocity measurements only allow for calculation of anisotropic parameters &#x003b5; and &#x003b3;
Total porosity was measured using a method based on the Boyle-Mariotte Law
Uniaxial compression experiments were performed on 26 samples using a servo-hydraulically controlled deformation apparatus (MTS)
LVDTS wrapped around the samples monitored axial and lateral strain at constant deformation rates of 10&#x02013;3&#x000a0;mm/s before abrupt failure at 0.1&#x000a0;mm/min after failure
These points correspond to an axial strain rate of less than 1 &#x000d7; 10&#x02212;5s&#x02212;1
The slope of stress-strain curves then provided estimates for a secant Young&#x02019;s modulus,&#x00395;S
The measurement error in stress and strain was less than 4%
a value which gave corresponding uncertainties in Young&#x02019;s moduli of about 20%
These tests were only performed on bedding-normal samples to lessen the influence of sample bedding and lamination on estimates of brittle failure properties
TOC ranged from 2.0% to 7.87% with an average of 4.19%
The high TOC lithofacies group is interpreted to have formed in a deep water shelf environment with high paleoproductivity of planskton under anoxic condition
Core material of this lithofacies exhibits thin
Lithofacies classification based on TOC content and ternary diagram of mineralogy of shale samples
(A) Ternary diagram for samples with TOC&#x02265;2%
(B) Ternary diagram for samples with TOC&#x0003c;2%
ORSS: Organic-rich siliceous shale; ORMS: Organic-rich mixed shale; OMMS: Organic-moderate mixed shale; OMAS: Organic-moderate argillaceous shale
Trace minerals detected by XRD include pyrite
This lithofacies is distinguished by its higher relative clay and carbonate content compared to the organic-rich lithofacies
The TOC content of the organic-moderate lithofacies ranges from 0.35% to 1.73% with an average of 1.02%
The organic-moderate shale lithofacies is interpreted to have formed in a shallow water shelf environment under dysoxic condition
The millimeter to centimeter scale silty belts in this lithofacies indicate higher energy conditions of shallow water environments
Thin sections and core samples of the organic-moderate lithofacies contain only a few graptolites
feldspar and pyrite exist in a matrix of elongated
which are primarily localized within pyrite framboids and dissolution particles having an average diameter of less than 400&#x000a0;nm
(A) organic-matter pores (OM pore) and interparticle pores (Sample C37; TOC: 5.1%; Porosity: 3.2%; 2452&#x000a0;m)
(B) interparticle pores with the shape of elongated ellipsoid between aligned clay (Sample C15; TOC: 2.74%; Porosity: 2.8%; 2162&#x000a0;m)
(C) interparticle pores with triangular shape between rigid quartz grains (Sample C31; TOC: 3.5%; Porosity: 2.2%; 2375&#x000a0;m)
(D) intracrystalline pores within pyrite framboids (Sample C21; TOC: 2.7%; Porosity: 3.1%; 2288&#x000a0;m)
White rectangles are the magnification areas
(A) and (B) Very coarse microcrystalline quartz with surrounded alignment clay (Sample C7; TOC: 1.65%; Porosity: 1.8%; shallow water shelf)
(C) and (D) Compact fine microcrystalline quartz (Sample C51; TOC: 5.68%; Porosity: 4.2%; deep water shelf)
where data are sorted by sedimentary circumstance
we observe that microtexture related acoustic velocity variations are in good agreement with the strong control of sedimentary circumstance on velocity
we can speculate that the microtexture evolution of shale samples
reflects the difference of sedimentary circumstance
strong control of rock microtexture on acoustic velocity also indicates the influence of sedimentary circumstance on velocity
Effect of microtexture variations on velocity of shale samples
(A) and (B) Velocity variations with quartz content
where data are sorted by clay content and sedimentary circumstance
respectively (A) SEM photomicrographs of clay as load-bearing grains (Sample C24; Clay: 43.7%; Quartz: 26%; TOC: 0.92%) (B) SEM photomicrographs of clay and quartz jointly as load-bearing grains (Sample C52; Clay: 32.4%; Quartz: 51.2%; TOC: 6.26%) (C) SEM photomicrographs of quartz as load-bearing grains (Sample C33; Clay: 17.5%; Quartz: 55.3%; TOC: 4.7%)
Database of mineral content and rock physical properties of sales sample at 30&#x000a0;MPa confining pressure
All shale samples are assumed to have transverse isotropic (TI) symmetry, with symmetry axis normal to the lamination or bedding plane. Five independent elastic constants C11, C33, C44, C66 and C13 are therefore needed to fully describe shale elastic properties. These can be obtained experimentally from measured velocity and density. Following <a href="#B63">Thomsen (1986)</a>
two important anisotropy parameters are defined as:
it is rational to speculate that anisotropy caused by the alignment of lenticular kerogen is not remarkable for Longmaxi Formation shale
except for samples with strong preferred orientation of clay minerals from the upper part of the Longmaxi Formation
where bed-parallel kerogen lenses along elongated pore within clay platelets can be observed
FIGURE 7. Anisotropy parameter &#x003b5; versus kerogen content for Wufeng-Longmaxi Formation shales and some mature and immature shales from Bakken shales displayed on the background of the modified Backus model for two-layer illite/kerogen composite (<a href="#B69">Vernik and Nur, 1992</a>)
Whole rock major element analyses of shale samples
In addition to organic matter distribution, the alignment of platy clay particles can also cause velocity anisotropy. <a href="#F8">Figure 8</a> plots the two major anisotropy parameters &#x003b5; and&#x003b3;as function of clay content at an effective pressure of 30&#x000a0;MPa
The data clearly show increasing &#x003b5; and &#x003b3; values with increasing clay content but with considerable variation in &#x003b5; and &#x003b3; values
This scatter does not apparently reflect variation in kerogen content as samples with relatively high &#x003b5; and&#x003b3; values give low TOC values
Organic matter distribution in pores also limits its influence on velocity anisotropy
Data plotted according to depositional environment showed a revealing trend
shale samples from deep water shelf environments exhibit lower velocity anisotropy values relative to samples from shallow water shelf environments
These properties imply that alignment of platy clay particles is still primarily account for the velocity anisotropy of post-mature Longmaxi Formation shale
that for Longmaxi Formation shale in different dispositional environment
compaction and associated alignment of clay particles is very different
Relatively weak compaction and alignment of clay particles is observed in the shale samples from deep water shelf circumstance
consistently with lower velocity anisotropy in the samples
Note that shale samples from deep water circumstance are characterized by quartz-supported framework
which will enhance effectively the preservation of intergranular pores in compaction; moreover
weaken the alignment of clay particles by intervening them from compactional rearrangement
Anisotropy parameters &#x003b5;(A) and &#x003b3;(B) as function of clay content of shale samples
Data points are sorted by clay content and sedimentary circumstance and TOC content (color bar)
In accordance with this transition in the shape of curves
samples C35 and C55 showed brittle fracture with typical splitting failure
Samples C14 and C28 developed a single shear crack
indicating the ductile nature of rock samples
Samples C1 and C41 showed conjugate shear cracks indicating semibrittle deformation (transitional between brittle and plastic deformation)
The observed differences are likely attributed not only to composition
Typical stress-strain curves of the shale samples (A) and fracture patterns (B&#x02013;G) (T represents tensile crack and tensile shear crack in the figure)
Microscopic crack characteristics of the typical shale samples after fracturing
(A) Microscopic crack characteristics of sample C14
(B) Microscopic crack characteristics of sample C28
(C) Microscopic crack characteristics of sample C35
(D) Microscopic crack characteristics of sample C55
The crack has not been infilled by other minerals demonstrating its opening during fracturing
These &#x0201c;Y&#x0201d; shaped cracks could connect to form a complex network resulting in the final splitting failure mode
Crossplot of static Young&#x02019;s modulus with major mineral composition
(A) Crossplot between static Young&#x02019;s modulus and quartz content
(B) Crossplot between static Young&#x02019;s modulus and carbonate content
(C) Crossplot between static Young&#x02019;s modulus and carbonate content
(D) Crossplot between static Young&#x02019;s modulus and TOC content
These weaker correlations still confirm that microtexture of shale samples (rather than mineral composition) exerts the strongest influence on static elastic properties of the Longmaxi Formation
Although all the samples analyzed derive from the same formation
the upper and lower members of the Longmaxi Formation (shallow water and deep water shelf environments
respectively) show systematic differences in their elastic behavior
These differences help constrain the interpretation of depositional and diagenetic factors from the mechanical properties of shale
Typical characteristics of quartz in shale samples
(A) SEM photomicrographs of shale sample C8 from the upper part of the Wufeng-Longmaxi Formation shale (mQz: microcrystalline quartz)
Discrete microcrystalline quartz embedded in the fine-grained illitized smectitic clay matrix
(B) SEM photomicrographs of shale sample C39 from the lower part of the Wufeng-Longmaxi Formation shale
Microcrystalline quartz formed coalescent aggregates
CL-A corresponding CL spectrum of extrabasinal quartz
CL-B corresponding CL spectrum of authigenic quartz sourced from smectite to illite reaction
CL-C and CL-D corresponding CL spectrum of biogenic quartz
it can be seen that the derivation of microcrystalline quartz in the two shale units are very different
Very coarse microcrystalline quartz within clay matrix in samples from upper part is mainly soured from smectite to illite reaction
whilst compact fine microcrystalline quartz in samples from lower part is mainly biogenic origin
FIGURE 13. (A) Crossplot of Si and Al of Wufeng-Longmaxi Formation shale on the background of illite Si/Al line and carbonate dilution line (<a href="#B53">Rowe et al., 2008</a>)
Bioenic quartz is distinguished from extrabasinal quartz by the slope
Data points are sorted by sedimentary circumstance
These trends affirm that the 38% quartz content threshold effectively differentiates between extrabasinal and biogenic quartz contributions
Proxies described above indicate extrabasinal quartz contribution in samples from the upper Longmaxi Formation and a major biogenic quartz contribution for samples from the lower Longmaxi Formation
This model is also consistent with our SEM&#x02013;CL work and geochemical analysis
Most important factors controlling elastic properties of reservoir rock at great burial depth are the primary sediment composition
sedimentary environment and subsequent diagenetic processes
The mechanical and chemical compaction of sediment during diagenesis drives the rock towards higher mechanical and chemical stability
Effective stress from overburden at temperatures below 70&#x02013;80&#x000b0;C causes mechanical compaction
shifting and ductile deformation of clay particles
These processes diminish porosity and create an aligned clay fabric
At greater depth (higher temperature) compaction in shales is mostly chemical and cementation resulting from mineral reactions
will dramatically increase the rock strength
in company with the further reduction of porosity and permeability
which will in most cases effectively shut down the mechanical compaction
mechanical compaction and chemical compaction are commonly considered as two sequential processes controlling the elastic properties of shales during burial
the stratigraphic difference in depth between the two part of Wufeng-Longmaxi Formation shales cannot explain the major difference in the macroscopic seismic elastic and geomechanical behaviors
as the maximum effective stresses and temperatures the two formations have undergone during burial and uplift must have been practically the same
Precipitation of illite and quartz will cause a sharp increase in matrix rigidity and prevent mechanical compaction
for the upper part of the Longmaxi Formation shales
it is rational to speculate that mechanical compaction and chemical compaction are two sequential processes in controlling elastic properties
Carbonate cement in samples from upper part of Longmaxi Formation is another critical component with respect to burial diagenesis
Relatively moderate amounts of carbonate cement in samples can results in high velocity and mechanical strength at shallow depth
Conceptual model summarizing the depositional and diagenetic processes of the Wufeng-Longmaxi Formation shale
The salient differences in microtexture and diagenetic evolution between the upper and lower Longmaxi Formation shales can be used to interpret contrasting acoustic and geomechanical properties as measured in the laboratory
Samples from the upper and lower parts of the Longmaxi Formation specifically differed in terms of brittleness
relations between static Young&#x02019;s modulus versus composition
their seismic velocity versus quartz content relationships and seismic velocity versus porosity (TOC content) relationships
the relationship between static Young&#x02019;s modulus and quartz content also indicates variation in load-bearing grains of shale samples
These trends indicate that quartz primarily has an extrabasinal origin in samples with quartz content &#x0003c;38%
whereas it is predominantly biogenic in origin in samples with quartz content &#x0003e;38%
ellipsoid shapes are often aligned parallel to bedding
This type of porosity is associated with considerable velocity variation
including intraparticle pores within framboids and other unstable phases (e.g.
clay and calcite) also impose considerable uncertainty in velocity interpretation
the strong clay alignment observed in the samples from upper part of the Longmaxi Formation Shales suggests the possible contribution of the semectite-illitization transformation to the overall velocity anisotropy
This study focused primarily on the influence of diagenetic and microstructural factors on macroscopic seismic elastic and geomechanical behaviors
This research performed laboratory measurements of acoustic and geomechanical properties along with detailed petrographic
geochemical analysis of 82 high-maturity shales from core samples of the Longmaxi Formation in the southeast Sichuan Basin
Interpretation of the data revealed how depositional history can influence acoustic and geomechanical properties
which finally exerts a critical influence on the reservoir quality and the physical properties of the shales
we have shown that microtexture and compositional reorganization of Longmaxi Formation shale was affected by the syn-depositional chemical reactivity of the primary grain assemblage
The lower part of the Longmaxi Formation formed in a deep water shelf environment where early cementation by biogenic quartz formed interlocking
contiguous quartz cement with limited mechanical interfaces
This biogenetic quartz cement thus assumed the role of a load bearing framework which effectively decreased subsequent mechanical compaction during burial
A very early clay fabrics and primary intergranular pores were effectively preserved
The upper part of the Longmaxi Formation formed in a shallow water shelf environment
clay minerals experienced normal compaction to form elongated ellipsoidal pores and a pervasively aligned clay fabric with apparent mechanic interface that played a load-bearing role
Si-Al relationships and trace element parameters such as Zr and Ti support the interpretation of a clay-supported framework for these samples
The microstructural differences between the upper and lower Longmaxi shales exert a primary influence on their macroscopic acoustic and geomechanical behaviors
A &#x0201c;V&#x0201d; shaped trend in seismic velocities and static Young&#x02019;s modulus plotted as function of quartz content for example clearly differentiates the elastic response of clay-supported and quartz-supported samples
The influence of porosity and TOC content on velocity is undeniable but velocity variation could be seen as a more direct result of the evolution of microstructure such as the load-bearing
Alignment of platy clay particles is the dominant factor in causing velocity anisotropy observed in Longmaxi Formation samples
apparent velocity anisotropy discrepancy could be observed as a reflection of the different compaction during burial
Microtexture also exerts a strong influence on the deformation mode
Samples with quartz-supported matrix (from reprecipitation of biogenic quartz cement) exhibit typical elastic deformation and splitting failure modes
samples with clay-supported microtexture show more plastic deformation caused by a heterogeneous medium with a mechanical interface between stiff minerals and the more ductile clay matrix
these results provide insights for the role of depositional and diagenetic controls on the microtexture and resulting rock properties of Wufeng-Longmaxi Formation Shales that could be applied positively to practical seismic-based &#x0201c;sweet-spots&#x0201d; prospecting of gas shale reservoir
All authors listed have made a substantial
and intellectual contribution to the work and approved it for publication
QZ and WG are employed by the company Petrochina
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<a href="https://doi.org/10.1016/j.jngse.2016.11.024">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Effect+of+lithofacies+on+gas+storage+capacity+of+marine+and+continental+shales+in+the+Sichuan+Basin,+China&amp;btnG=">Google Scholar</a>
Heterogeneity of the lower silurian Longmaxi marine shale in the southeast Sichuan Basin of China
<a href="https://doi.org/10.1016/j.marpetgeo.2015.04.003">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Heterogeneity+of+the+lower+silurian+Longmaxi+marine+shale+in+the+southeast+Sichuan+Basin+of+China&amp;btnG=">Google Scholar</a>
Hirnantian (latest ordovician) graptolites from the upper yangtze region
<a href="https://doi.org/10.1111/j.1475-4983.2005.00453.x">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Hirnantian+(latest+ordovician)+graptolites+from+the+upper+yangtze+region,+China&amp;btnG=">Google Scholar</a>
Late Ordovician to earliest Silurian graptolite and brachiopod biozonation from the Yangtze region,South China
<a href="https://doi.org/10.1017/S0016756800004702">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Late+Ordovician+to+earliest+Silurian+graptolite+and+brachiopod+biozonation+from+the+Yangtze+region,South+China,+with+a+global+correlation&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1306/61EEDDBE-173E-11D7-8645000102C1865D">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fractured+shale-gas+systems&amp;btnG=">Google Scholar</a>
Diagenetic reorientation of phyllosilicate minerals in paleogene mudstones of the podhale basin
<a href="https://doi.org/10.1346/ccmn.2008.0560109">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Diagenetic+reorientation+of+phyllosilicate+minerals+in+paleogene+mudstones+of+the+podhale+basin,+southern+Poland&amp;btnG=">Google Scholar</a>
The velocity and attenuation anisotropy of shale at ultrasonic frequency
<a href="https://doi.org/10.1088/1742-2132/6/3/006">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+velocity+and+attenuation+anisotropy+of+shale+at+ultrasonic+frequency&amp;btnG=">Google Scholar</a>
Compaction-driven evolution of porosity and permeability in natural mudstones: an experimental study
<a href="https://doi.org/10.1029/97jb02540">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Compaction-driven+evolution+of+porosity+and+permeability+in+natural+mudstones:+an+experimental+study&amp;btnG=">Google Scholar</a>
microcracks and stress field on shale anisotropy
<a href="https://doi.org/10.1111/j.1365-246x.2006.02834.x">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Impact+of+fabric,+microcracks+and+stress+field+on+shale+anisotropy&amp;btnG=">Google Scholar</a>
Geomechanical and ultrasonic characterization of a norwegian sea shale
<a href="https://doi.org/10.1190/1.3569599">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geomechanical+and+ultrasonic+characterization+of+a+norwegian+sea+shale&amp;btnG=">Google Scholar</a>
The impact of rock composition on geomechanical properties of a shale formation: middle and Upper Devonian Horn River Group shale
<a href="https://doi.org/10.1306/07251615199">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+impact+of+rock+composition+on+geomechanical+properties+of+a+shale+formation:+middle+and+Upper+Devonian+Horn+River+Group+shale,+Northeast+British+Columbia,+Canada&amp;btnG=">Google Scholar</a>
Mechanical properties of organic matter in shales mapped at the nanometer scale
<a href="https://doi.org/10.1016/j.marpetgeo.2014.09.007">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mechanical+properties+of+organic+matter+in+shales+mapped+at+the+nanometer+scale&amp;btnG=">Google Scholar</a>
spectral characteristics and practical applications of the cathodoluminescence (CL) of quartz &#x02013; a review
<a href="https://doi.org/10.1007/s007100170040">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Origin,+spectral+characteristics+and+practical+applications+of+the+cathodoluminescence+(CL)+of+quartz+–+a+review&amp;btnG=">Google Scholar</a>
The forming and evolution of Sichuan Basin
The lithofacies and reservoir characteristics of the upper ordovician and lower silurian black shale in the southern sichuan basin and its periphery
<a href="https://doi.org/10.1016/j.marpetgeo.2016.04.014">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+lithofacies+and+reservoir+characteristics+of+the+upper+ordovician+and+lower+silurian+black+shale+in+the+southern+sichuan+basin+and+its+periphery,+China&amp;btnG=">Google Scholar</a>
Effects of porosity and clay content on wave velocities in sandstones
<a href="https://doi.org/10.1190/1.1442062">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Effects+of+porosity+and+clay+content+on+wave+velocities+in+sandstones&amp;btnG=">Google Scholar</a>
Evidence for multiple stages of oil cracking and thermochemical sulfate reduction in the Puguang Gas Field
<a href="https://doi.org/10.1306/01210807090">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Evidence+for+multiple+stages+of+oil+cracking+and+thermochemical+sulfate+reduction+in+the+Puguang+Gas+Field,+Sichuan+basin,+China&amp;btnG=">Google Scholar</a>
Anisotropic effective&#x02010;medium modeling of the elastic properties of shales
<a href="https://doi.org/10.1190/1.1443546">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Anisotropic+effective&#x02010;medium+modeling+of+the+elastic+properties+of+shales&amp;btnG=">Google Scholar</a>
Mechanical and petrophysical properties of North Sea shales
<a href="https://doi.org/10.1016/s0148-9062(98)00162-4">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mechanical+and+petrophysical+properties+of+North+Sea+shales&amp;btnG=">Google Scholar</a>
An experimental investigation of shale mechanical properties through drained and undrained test mechanisms
<a href="https://doi.org/10.1007/s00603-013-0377-8">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=An+experimental+investigation+of+shale+mechanical+properties+through+drained+and+undrained+test+mechanisms&amp;btnG=">Google Scholar</a>
Unconventional shale-gas systems: the Mississippian Barnett Shale of north-central Texas as one model for thermogenic shale-gas assessment
<a href="https://doi.org/10.1306/12190606068">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Unconventional+shale-gas+systems:+the+Mississippian+Barnett+Shale+of+north-central+Texas+as+one+model+for+thermogenic+shale-gas+assessment&amp;btnG=">Google Scholar</a>
Unconventional hydrocarbon resources in China and the prospect of exploration and development
<a href="https://doi.org/10.1016/s1876-3804(12)60026-3">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Unconventional+hydrocarbon+resources+in+China+and+the+prospect+of+exploration+and+development&amp;btnG=">Google Scholar</a>
Controlling factors on the enrichment and high productivity of shale gas in the Wufeng-Longmaxi Formations
<a href="https://doi.org/10.13745/j.esf.2016.01.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Controlling+factors+on+the+enrichment+and+high+productivity+of+shale+gas+in+the+Wufeng-Longmaxi+Formations,+southeastern+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Effect of grain scale alignment on seismic anisotropy and reflectivity of shales
<a href="https://doi.org/10.1046/j.1365-2478.2003.00405.x">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Effect+of+grain+scale+alignment+on+seismic+anisotropy+and+reflectivity+of+shales&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1029/95jb00031">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Seismic+anisotropy+of+shales&amp;btnG=">Google Scholar</a>
The importance of geochemical parameters and shale composition on rock mechanical properties of gas shale reservoirs: a case study from the Kockatea Shale and Carynginia Formation from the Perth Basin
<a href="https://doi.org/10.1007/s00603-014-0617-6">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+importance+of+geochemical+parameters+and+shale+composition+on+rock+mechanical+properties+of+gas+shale+reservoirs:+a+case+study+from+the+Kockatea+Shale+and+Carynginia+Formation+from+the+Perth+Basin,+Western+Australia&amp;btnG=">Google Scholar</a>
The potential and exploring progress of unconventional hydrocarbon resources in sinopec
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+potential+and+exploring+progress+of+unconventional+hydrocarbon+resources+in+sinopec&amp;btnG=">Google Scholar</a>
Experimental investigation of the effect of temperature on the mechanical behavior of tournemire shale
<a href="https://doi.org/10.1016/j.ijrmms.2014.05.007">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Experimental+investigation+of+the+effect+of+temperature+on+the+mechanical+behavior+of+tournemire+shale&amp;btnG=">Google Scholar</a>
Unconventional gas - a review of regional and global resource estimates
<a href="https://doi.org/10.1016/j.energy.2013.01.048">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Unconventional+gas+-+a+review+of+regional+and+global+resource+estimates&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1306/12011111129">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Grain+assemblages+and+strong+diagenetic+overprinting+in+siliceous+mudrocks,+barnett+shale+(mississippian),+fort+worth+basin,+Texas&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1190/1.2944161">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Elastic+properties+of+clay+minerals&amp;btnG=">Google Scholar</a>
Microporosity in micritic limestones: a review
<a href="https://doi.org/10.1016/0037-0738(89)90132-2">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Microporosity+in+micritic+limestones:+a+review&amp;btnG=">Google Scholar</a>
I&#x02013;S precipitation in pore space as the cause of geopressuring in Mesozoic mudstones
<a href="https://doi.org/10.2138/am-2002-11-1208">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=I–S+precipitation+in+pore+space+as+the+cause+of+geopressuring+in+Mesozoic+mudstones,+Egersund+Basin,+Norwegian+continental+shelf&amp;btnG=">Google Scholar</a>
The conversion of smectite to illite during diagenesis: evidence from some illitic clays from bentonites and sandstones
<a href="https://doi.org/10.1180/minmag.1985.049.352.10">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+conversion+of+smectite+to+illite+during+diagenesis:+evidence+from+some+illitic+clays+from+bentonites+and+sandstones&amp;btnG=">Google Scholar</a>
Laboratory investigation of the mechanical behaviour of Tournemire shale
<a href="https://doi.org/10.1016/s1365-1609(97)80029-9">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Laboratory+investigation+of+the+mechanical+behaviour+of+Tournemire+shale&amp;btnG=">Google Scholar</a>
Clay mineral diagenesis and quartz cementation in mudstones: the effects of smectite to illite reaction on rock properties
<a href="https://doi.org/10.1016/j.marpetgeo.2008.01.021">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Clay+mineral+diagenesis+and+quartz+cementation+in+mudstones:+the+effects+of+smectite+to+illite+reaction+on+rock+properties&amp;btnG=">Google Scholar</a>
Texture and diagenesis of ordovician shale from the canning basin
western Australia: implications for elastic anisotropy and geomechanical properties
<a href="https://doi.org/10.1016/j.marpetgeo.2014.07.017">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Texture+and+diagenesis+of+ordovician+shale+from+the+canning+basin,+western+Australia:+implications+for+elastic+anisotropy+and+geomechanical+properties&amp;btnG=">Google Scholar</a>
Acoustic character logs and their applications in formation evaluation
<a href="https://doi.org/10.2118/452-pa">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Acoustic+character+logs+and+their+applications+in+formation+evaluation&amp;btnG=">Google Scholar</a>
&#x0201c;A practical use of shale petrophysics for stimulation design optimization:All shale plays are not clones ofthe barnett shale,&#x0201d; in SPE Annual Technical Conference and Exhibition
<a href="https://doi.org/10.2118/115258-ms">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+practical+use+of+shale+petrophysics+for+stimulation+design+optimization:All+shale+plays+are+not+clones+ofthe+barnett+shale&amp;btnG=">Google Scholar</a>
Characterizing the shale gas resource potential of Devonian-Mississippian strata in the Western Canada sedimentary basin: application of an integrated formation evaluation
<a href="https://doi.org/10.1306/09040707048">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characterizing+the+shale+gas+resource+potential+of+Devonian-Mississippian+strata+in+the+Western+Canada+sedimentary+basin:+application+of+an+integrated+formation+evaluation&amp;btnG=">Google Scholar</a>
Texas: bulk geochemical inferences and Mo-TOC constraints on the severity of hydrographic restriction
<a href="https://doi.org/10.1016/j.chemgeo.2008.08.006">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mississippian+barnett+formation,+fort+worth+basin,+Texas:+bulk+geochemical+inferences+and+Mo-TOC+constraints+on+the+severity+of+hydrographic+restriction&amp;btnG=">Google Scholar</a>
What controls the mechanical properties of shale rocks
- Part I: strength and Young&#x00027;s modulus
<a href="https://doi.org/10.1016/j.petrol.2015.10.028">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=What+controls+the+mechanical+properties+of+shale+rocks?+-+Part+I:+strength+and+Young's+modulus&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1029/93jb02579">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+elastic+anisotrophy+of+shales&amp;btnG=">Google Scholar</a>
Microcrack-induced seismic anisotropy of sedimentary rocks
<a href="https://doi.org/10.1029/91jb01232">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Microcrack-induced+seismic+anisotropy+of+sedimentary+rocks&amp;btnG=">Google Scholar</a>
Ultrasonic measurement of anisotropy on the kimmeridge shale
<a href="https://doi.org/10.1190/1.1815791">CrossRef Full Text</a>
Mechanical properties of shale-gas reservoir rocks - Part 1: static and dynamic elastic properties and anisotropy
<a href="https://doi.org/10.1190/geo2013-0050.1">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Mechanical+properties+of+shale-gas+reservoir+rocks+-+Part+1:+static+and+dynamic+elastic+properties+and+anisotropy&amp;btnG=">Google Scholar</a>
Fundamentals and use of potassium/polymer drilling fluids to minimize drilling and completion problems associated with hydratable clays
<a href="https://doi.org/10.2118/10100-pa">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fundamentals+and+use+of+potassium/polymer+drilling+fluids+to+minimize+drilling+and+completion+problems+associated+with+hydratable+clays&amp;btnG=">Google Scholar</a>
Distribution of black shale in the wufeng-longmaxi formations (ordovician- silurian)
south China: major controlling factors and implications
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Distribution+of+black+shale+in+the+wufeng-longmaxi+formations+(ordovician-+silurian),+south+China:+major+controlling+factors+and+implications&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1190/1.1442051">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Weak+elastic+anisotropy&amp;btnG=">Google Scholar</a>
Quartz cementation in mudstones: sheet-like quartz cement from clay mineral reactions during burial
<a href="https://doi.org/10.1144/1354-079310-028">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Quartz+cementation+in+mudstones:+sheet-like+quartz+cement+from+clay+mineral+reactions+during+burial&amp;btnG=">Google Scholar</a>
Emerging methodologies to characterize the rock physics properties of organic-rich shales
<a href="https://doi.org/10.1190/1.2944163">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Emerging+methodologies+to+characterize+the+rock+physics+properties+of+organic-rich+shales&amp;btnG=">Google Scholar</a>
Elastic anisotropy of source rocks: implications for hydrocarbon generation and primary migration
<a href="https://doi.org/10.1190/1.1444461">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Elastic+anisotropy+of+source+rocks:+implications+for+hydrocarbon+generation+and+primary+migration&amp;btnG=">Google Scholar</a>
Velocity anisotropy in shales: a petrophysical study
<a href="https://doi.org/10.1190/1.1444162">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Velocity+anisotropy+in+shales:+a+petrophysical+study&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1190/1.3567263">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Rock+physics+of+organic+shales&amp;btnG=">Google Scholar</a>
Ultrasonic velocity and anisotropy of hydrocarbon source rocks
<a href="https://doi.org/10.1190/1.1443286">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Ultrasonic+velocity+and+anisotropy+of+hydrocarbon+source+rocks&amp;btnG=">Google Scholar</a>
Biogenic silica of organic-rich shale in Sichuan Basin and its significance for shale gas
Acta Scientiarum Naturalium Universitatis Pekinensis 50 (3)
<a href="https://doi.org/10.13209/j.0479-8023.2014.079">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Biogenic+silica+of+organic-rich+shale+in+Sichuan+Basin+and+its+significance+for+shale+gas&amp;btnG=">Google Scholar</a>
Shale sequence stratigraphy of Wufeng-Longmaxi Formation in Southern Sichuan and their control on reservior
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Shale+sequence+stratigraphy+of+Wufeng-Longmaxi+Formation+in+Southern+Sichuan+and+their+control+on+reservior&amp;btnG=">Google Scholar</a>
doi:10.1306/212F86AC-2B24-11D7-8648000102C1865D
<a href="https://doi.org/10.1306/212F86AC-2B24-11D7-8648000102C1865D">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Silica+diagenesis,+I.+Solubility+controls&amp;btnG=">Google Scholar</a>
&#x0201c;Application of inorganic whole rock geochemistry to shale resource plays,&#x0201d; in Canadian unconventional resources and international petroleum conference (Calgary
<a href="https://doi.org/10.2118/137946-MS">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Application+of+inorganic+whole+rock+geochemistry+to+shale+resource+plays&amp;btnG=">Google Scholar</a>
Geochemical characteristics and depositional environments of cherts and associated rocks in the franciscan and shimanto terranes
65&#x02013;108doi:10.1016/0037-0738(87)90017-0
<a href="https://doi.org/10.1016/0037-0738(87)90017-0">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geochemical+characteristics+and+depositional+environments+of+cherts+and+associated+rocks+in+the+franciscan+and+shimanto+terranes&amp;btnG=">Google Scholar</a>
Smectite-to-illite reactions in Salton Sea shales: a transmission and analytical electron microscopy study
doi:10.1306/212F8B20-2B24-11D7-8648000102C1865D
<a href="https://doi.org/10.1306/212F8B20-2B24-11D7-8648000102C1865D">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Smectite-to-illite+reactions+in+Salton+Sea+shales:+a+transmission+and+analytical+electron+microscopy+study&amp;btnG=">Google Scholar</a>
Acoustic velocity and attenuation of rocks: isotropy
<a href="https://doi.org/10.1190/1.1821910">CrossRef Full Text</a>
Tang G and Zhao J (2021) Depositional and Diagenetic Controls on Macroscopic Acoustic and Geomechanical Behaviors in Wufeng-Longmaxi Formation Shale
Received: 03 November 2020; Accepted: 11 February 2021;Published: 18 March 2021
Copyright &#x000a9; 2021 Deng, Wang, Zhao, Guo, Tang and Zhao. This is an open-access article distributed under the terms of the <a rel="license" href="http://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution License (CC BY).</a> The use
&#x0002a;Correspondence: Jixin Deng, <a id="encmail">ZGVuZ2ppeGluQGNkdXQuY24=</a>; Chongyi Wang, <a id="encmail">Y2RsZ3JvY2twaHlzaWNzQGdtYWlsLmNvbQ==</a>
We meet up at the 7-Eleven beneath the apartment block in Taichung’s Wufeng District (霧峰), where Nathan Miller lives weekdays (weekends are spent with his wife and daughter in Taoyuan). Breakfast swallowed, Miller suggests we first ride around the corner to Guangfu Junior High School (光復國中). 
Passing rows of dilapidated buildings along Sinsheng Road (新生路), a few of which have been renovated to operate as artsy-cutesy businesses, I am reminded that Wufeng suffered badly in the 7.3-magnitude 921 Earthquake, and many more than 100 locals would have died had it occurred during school hours and not at 1:47am.  
Apart from a new canopy roof and some supporting beams, the collapsed school, fault rupture and elevated riverbank have been left pretty much as they were. Renamed the 921 Earthquake Museum of Taiwan (九二一地震教育園區) in 2007, the school invites visitors to learn about earth sciences in a natural setting. 
“You can easily spend half a day going round the various exhibits,” says Miller, who has brought his daughter here twice, though they have yet to go to the “quake room” to experience what such a macroseism feels like. He’s keen to go back, since he wasn’t in Taiwan in 1999, and his daughter wasn’t born then. 
We head off up Provincial Highway 3, which is busy at this hour with both commuters and trucks. Seeing a couple of turn-offs to Jhongsing New Village (中興新村), where Chiang Kai-shek’s (蔣介石) Chinese Nationalist Party (KMT) moved the provincial government in 1956, I suggest a detour. But Miller, who has a school meeting at 3pm, says it’s pretty interesting but deserves a half-day of its own.
“You’ll get a kick out of this,” he says after we’ve pedaled another 20 minutes. “Everyone stops here for a selfie, but I don’t know if your newspaper will print it.”
He’s referring to a 3m-tall sculpture of two pigs making love, the male on top with its tongue hanging out lasciviously. Beneath the pair is the inscription Shengshengbuxi (生生不息), normally meaning “life without end” but, in this context, perhaps “coitus uninterruptus.”
From newspaper reports, this turns out to have been a 2010 publicity stunt by a Nantou meat market wishing to promote a more positive image than mass slaughter. Parents of children at a nearby junior high school complained, however, so it ended up here on top of a hill. (Some other wag complained it was only a bad example for children since it is biologically inaccurate: the female would be standing up if she was in season.) 
We turn onto Provincial Highway 16 and, before long, up a side road to Jiji Township (集集), epicenter of the eponymous 1999 earthquake. It now oscillates between being a sleepy alpine village and vibrant tourist town. 
Today, a film crew is in town making an episode of a soap opera, though maybe it is a soap advertisement, albeit with an unusually complex narrative.
Nearby at 252 Minsheng Road, the Naturally Vegetarian (天然素食; Chinese only) restaurant offers a wide range of tasty noodle and rice dishes.
Lunch over, we follow the Jhuoshuei River (濁水溪) upstream to Shueili (水里), where the local Snake Kiln has been developed into a major visitor attraction since my last visit over two decades ago. In addition to the century-old, wood-fired, 30m-long brick kiln, there are now a museum, art galleries, lecture rooms, shops, DIY pottery classes and, standing 6.68m tall, the world’s largest kiln-fired pot.
And yes, you’ll probably need at least another half-day to do this place — and the NT$150 ticket price — justice.
Presumably the Thao Aborigines gave it 10 out of 10 since they moved to live here after, according to legend (which, in other contexts, might be called oral history), a tribe member inadvertently discovered the fish-filled lake when following a white deer he was hunting.
From here, Miller has around 55km of fast descent back to Wufeng and that 3pm meeting. I, meanwhile, will ride the undulating 30km through Ita Thao (伊達邵; Barawbaw in the Thao language), largely rebuilt since 80 percent of structures were felled by the quake, and on around the lake, since, not having an appointment myself, I still have a half-day to spare.
Mark Caltonhill bikes, and writes, and writes about bikes.
Volume 12 - 2024 | <a class="ArticleLayoutHeader__info__doi" href="https://doi.org/10.3389/feart.2024.1361706">https://doi.org/10.3389/feart.2024.1361706</a>
This article is part of the Research TopicAdvances of New Technologies in Seismic Exploration<a class="Link Link--linkType Link--maincolor Link--medium Link--icon Link--chevronRight Link--right" aria-label="View all 22 articles" href="https://www.frontiersin.org/research-topics/51829/advances-of-new-technologies-in-seismic-exploration/articles" target="_self" data-event="customLink-linkType-a_viewAll22Articles">View all 22 articles</a>
The H shale gas block in the Yangtze plate of China has undergone multistage tectonic evolution
which has resulted in the development of faults and natural fractures that are multistage
To precisely characterize the natural fractures
this study used the seismic attribute analysis method to conduct a multi-scale prediction and natural fracture modelling
manual fault interpretation and the conventional seismic attributes including variance attribute
curvature and edge detection are used to interpret large-to medium-scale faults
the ant-tracking attribute based on the divided-frequency seismic cubes is used to predict and quantitatively interpret the mid- and small-scale fractures; The third step is to quantitatively divide the ant-tracking attribute value into multiple scales and convert them linearly into fracture intensity
The fourth step is to establish a multi-scale fracture model
This approach has established a comprehensive prediction workflow
progressing from large-scale to small-scale analysis
and shifting from qualitative to quantitative assessment
Compared with traditional fracture prediction and modeling methods
this method not only enhances the accuracy
but also satisfies the engineering requirements of multi-scale modeling
By applying the method in the H shale gas block
we gained a microscopic understanding of the fractures
with a minimal occurrence of nearly EW trending faults/fractures
This method can be effectively applied to characterize multi-scale fractures in areas similar to the geological background of the H shale gas block
The impact of faults/natural fractures on shale gas preservation and exploitation
it is crucial to classify the fractures appropriately based on various engineering requirements and actual data
In order to characterize the spatial distribution of natural fracture system in shale reservoirs
improve the accuracy of fracture prediction
and reasonably divide the scale of the natural fractures
multi-scale fracture prediction and multi-scale fracture modelling were carried out by using seismic attribute analysis techniques taking the H shale gas block of the Yangtze Plate as the research object
the relatively larger-scale faults were qualitatively interpreted using optimized seismic multi-attributes combined with manual interpretation
to establish a macroscopic understanding of regional tectonics
the finer faults/fractures were predicted and quantitatively interpreted by ant-tracking attribute
to establish a microscopic understanding of regional fractures
the scales of ant tracking anomalies value are divided according to the comparison of ant tracking and discontinuity features of seismic sections
the divided ant tracking anomalies value is linearly converted into multi-scale fracture intensity
the multi-scale discrete fracture modeling is carried out
The assumption of the following methods is amplitude preservation processing of the seismic data
The noise suppression processing should meet the requirements of maintaining relatively amplitude
The amplitude compensation processing should also meet the requirement of maintaining relatively amplitude
the amplitude curve before and after spherical diffusion compensation should maintain the corresponding amplitude relationship in the vertical direction
The algorithm of the variance body is is outlined as follows: Initially, the variance value for each sample point is computed, Subsequently, the required variance value is derived through weighted normalization with a specified. The variance volume is then calculated by utilizing the following equation, which yields the variance value for a sampling point (Eqs <a href="#e1">1</a>&#x02013;<a href="#e6">6</a>)
the smaller the similarity between adjacent traces
xk&#x000af; represents the average amplitude of all traces at time k
Ai,j and Bi,j are the intermediate transition variable
Di,j indicates the variance value of the j th sampling point of the i th trace
&#x003c3;i,j represents the weighted variance value of the j th sampling point of the i th track
L is the time window length of variance (e.g.
N is the number of adjacent traces needed to calculate the variance value of a point (for example
W is the trigonometric weighting function of a sampling point in the time window
The variance value of each sampling point throughout the whole 3D seismic data body is calculated according to the aforementioned formula
ultimately yielding a new 3D variance attribute body
Curvature attribute is used to describe the degree of bending at a point on a curve or surface, whose mathematical definition is the ratio of angle to arc length change rate. It can be expressed using the second derivative of the point (Eq <a href="#e7">7</a>) (<a href="#B4">Cheng, 2020</a>; <a href="#B53">Zhang et al., 2021</a>)
For curvature calculations, least squares are typically used to fit a quadratic surface ux,y to obtain the surface and then the curvature attribute can be calculated as Eq <a href="#e8">8</a>
Curvature attributes are applied to evaluate the pattern distribution of geological bodies in geometric space, enabling the effective identification of geometric structures such as faults, fractures, bends and folds (<a href="#B47">Yang et al., 2015</a>; <a href="#B56">Zheng et al., 2019</a>). Curvature has clear geological implications, as shown in <a href="#F1">Figure 1</a>
When the stratum is horizontal or obliquely flat
the normal vectors of the stratum are parallel to each other and the curvature is zero
When the stratum is an anticline or uplifted
the normal vectors are divergent and the curvature is defined as positive
the normal vectors are convergent and the curvature is defined as negative
The absolute value of curvature is small when the occurrence of seismic events is wide and gentle
it is large when the stratum occurrence changes dramatically
the curvature attribute has been widely recognized for its effectiveness in fault detection
tectonic morphology identification and fracture prediction
Curvature attributes mainly include minimum curvature
an edge corresponds to a reflection of the grayscale discontinuity of the image pixel
whose surrounding pixels have step changes or roof changes in grayscale
Image edges carry rich in information and serve as crucial feature parameters for geo-target recognition and image interpretation
The essence of edge detection lies in calculating and extracting the demarcation line between targets
as well as between targets and backgrounds by mathematical algorithms
The discontinuous features of seismic response
such as small fractures and lenticular body edges
are manifested in the image as edge features
it becomes easier to discover and identify geological features
The ant algorithm, first proposed by Italian scholar <a href="#B7">Colorni et al. (1992)</a> in the early 1990s, is a heuristic bionic evolutionary algorithm based on population, which simulates the collective foraging behavior of ants in nature. To illustrate this principle, Colorni provided an example of an artificial ant algorithm, as shown in <a href="#F2">Figure 2</a>
they can either pass through H or C to reach point D before finally reaching the food source
The distance from point B to point H is twice the distance from point B to point C
The ants will leave pheromones along their path
the ants will randomly choose a path to forage
since the distance of path BHD is twice the distance of path BCD
the number of round trips of ants on path BCD is twice the number of round trips of ants on path BHD
the amount of pheromones left behind is also twice
the number of ants choosing path BCD afterward will be twice the number of ants on BHD
an increasing number of ants will choose the path BCD to forage
thus achieving the objective of foraging in the shortest time
SLB then applied &#x0201c;ant tracking&#x0201d; algorithm to the seismic attribute analysis in Petrel platfom
automatically analyzes and identifies fracture systems
resulting in the generation of an ant-tracking attribute with clear fracture traces
thereby enhancing the ability to extract geological information
Attribute fusion technology is generally categorized into linear fusion
the attribute fusion method employed involves linear proportional fusion
The specific approach is as follows: first
select relatively sensitive seismic attributes; Next
through multiple attribute fusion experiments
determine the optimal linear fusion proportion; Finally
fuse the selected attributes by setting appropriate proportions
it was determined that the Longmaxi-Wufeng formation displayed as a set of relatively continuous strong seismic events on seismic data
Previous studies have confirmed that the fractures in Yangtze area have the characteristics of multi-stage, multi-scale, multi-type and multi-strike (<a href="#B43">Xie et al., 2021</a>; <a href="#B1">Chen et al., 2022</a>; <a href="#B44">Xie et al., 2022</a>). In order to clarify the fracture development of Block H, we applied the multi-scale fracture prediction workflow shown in <a href="#F3">Figure 3</a>
All methods in the workflow are implemented on Petrel
which is a comprehensive geophysical and geological research platform
Longmaxi-Wufeng formation is the target formation
Workflow proposed in this study for multi-scale fracture prediction
various seismic attributes such as the RMS attribute
and edge detection attribute are extracted along the layers to analyze and determine the developmental characteristics of medium- and large-scale faults in the study area
making faults appear less crisp and potentially misleading interpreters
Given the distinct characteristics and differences between these two attributes
some fault responses are more linear on the edge detection attribute plane
Various seismic attributes along Longmaxi-Wufeng formation
(D) Fusion map combining max curvature and edge detection attribute
After comprehensively considering the advantages and disadvantages of each attribute, the curvature and edge detection attributes were selected for attribute fusion as they are more effective in fault identification. By fusing these attributes, the result (<a href="#F4">Figure 4D</a>) are obtained that combines the advantages of both attributes
reducing noise of curvature and the fault-thickening effect of edge detection attribute
The fused seismic attributes effectively provide a macroscopic understanding of the faults in the area
indicating the fault orientation and the intersection relationship between the faults for fault interpreters
By combining seismic sections for manual fault interpretation
we effectively reduced the multiplicity of fault interpretation
It can be observed that the main fault strikes are NW and NE
Manual fault polygons along Longmaxi-Wufeng formation
(A) Overlayed map with Fusion map by Max curvature and edge detection attribute
Manual multi-scale fault interpretation table
The ant tracking method used in the study is based on a published paper (<a href="#B44">Xie et al., 2022</a>)
which has been demonstrated to effectively enhance the accuracy of fracture identification
Unlike the traditional ant tracking based on full-frequency seismic volume
the method utilizes frequency-division seismic data
we have found that dividing the frequency into four or more parts not only increases the workload significantly but also leads to the loss of a considerable amount of effective fracture information due to the excessively narrow frequency bands
we believe that dividing the frequency into low
and high components using a step size of 15 Hz aligns with our work experience and avoids both the loss of valuable information and excessive workload
the full-frequency seismic volume was divided into low-frequency (0&#x02013;15 HZ)
and high-frequency (30&#x02013;45 Hz) cubes
Ant tracking calculations were then conducted on the frequency-division data and full-frequency data
The better ant tracking results were selected through a comparative analysis
they were fused to obtain the final fracture prediction result
effectively improving the fracture prediction
Stereonet of ant tracking for Orientation Filter (Black-gray represents exclusion
and white represents participation in the calculation)
Figure 7. Ant tracking result superimposed on seismic section (modified from <a href="#B44">Xie et al., 2022</a>)
(C) 30&#x02013;45 Hz (D) fused by 15&#x02013;30 Hz and 30&#x02013;45 Hz
This consistency serves as robust validation of the accuracy and reliability of the ant tracking technique in predicting fracture orientations
Ant tracking slices along Longmaxi-Wufeng formation
(B) Fused 15&#x02013;30 Hz and 30&#x02013;45 Hz
Fracture information of Wufeng formation around H1
Superimposed display of ant tracking and seismic data
(A) Strong ant tracking: big fault with obvious fault displacement
(B) Medium-strong ant tracking: medium fault/fracture belt with small fault displacement
(C) Weak ant tracking: possible fracture belt or small-scale fracture
Superimposed map of ant tracking slice and manually interpreted faults along Longmaxi-Wufeng formation The (A,B) seismic section demonstrates large-scale fault (red) with large ant tracking anomaly value
The (C,D) seismic section shows medium-scale faults (blue) with medium-strong ant tracking anomaly value
The (E,F) seismic section demonstrates small-scale faults (pink) with small ant tracking anomaly value
The characteristics of the ant tracking anomalies
Group 1 corresponds to large-to medium-scale faults
one or more seismic events are interrupted
making them easy to judge and interpret manually
They generally have a destructive effect on shale reservoirs and are not conducive to the preservation of shale gas
thus should be avoided as much as possible during well placement
Group 2 corresponds to the small-scale faults
extending from a few tens to hundreds of meters in the plane
the seismic events show a change in occurrence (distortion) or amplitude (weakening)
becoming more evident after ant tracking than the original seismic sections
These small-scale faults including fracture belts have an important influence on shale gas engineering construction
their presence affects the stability of the wellbore
When drilling and geological steering are carried out
wellbore collapse or mud losses may occur if shear slip occurs in the small-scale faults or the fracture belts
during the process of fracturing reconstruction
small-scale faults or the fracture belts will affect the efficiency of fracturing and the fractures expansion of hydraulic fracturing
difficulty in sand addition and other issues
Group 3 corresponds to fine-scale fault or extension of fracture belts
but can be observed in imaging log data and core data
Group 4 corresponds to micro-scale fractures with length of a few meters
These features are difficult to manually distinguish manually on seismic data
They can increase the storage space for shale gas and are beneficial for increasing shale gas production
Their spatial distribution is difficult to detect
which can be characterized by stochastic modeling when modelling
(A) Dip azimuth stereogram; (B) Dip histogram; (C) Fracture length histogram
Multi-scale fracture modelling for Longmaxi-Wufeng formation
(E) Fracture model of multi-scale fractures for Longmaxi-Wufeng formation
There hasn&#x02019;t been a unified multi-scale division standard on multi-scale fracture prediction
The method used in this paper is a combination of manual fault interpretation
seismic multi-attribute extraction and fusion technique
improved ant tracking technique and multi-scale fracture modeling
The innovation of this paper lies in the quantitative multi-scale division of fracture using ant tracking value
which is different from other papers and provides a solid data basis for fracture modeling
The significance of refined fault/fracture description in the form of multi-scale is shown in two aspects
traditional seismic attributes are used to represent the development of large-scale faults
we can easily gain a macro understanding of structural development
the ant tracking attribute is effective in refining small-scale fault/fractures and fracture belts
or electron microscopy (if available) is employed to describe micro-scale fractures
Refined fault/fracture description in the form of multi-scale realizes the progressive understanding of fracture from macro to micro
The establishment of natural fracture models with different scales utilizes mutually independent fracture groups
The mechanical properties of fractures at different scales vary
thus their impacts on drilling and completion engineering are also distinct
which can be applied in independently different scenarios
due to the large fault displacement of group 1 and 2
horizontal wells should not directly cross them during well location arrangement and construction
Fracture groups 3 and 4 may pose risks to drilling and completion engineering
attention should be paid to determining the risk control plan in advance to avoid wellbore collapse
Although each group of fracture models is independent
they form an integral whole and can be used together
The collective model can be utilized for subsequent geomechanical modeling
predicting the stability of natural fractures
studying the impact of natural fractures on hydraulic fracturing
and simulating the relationship between natural fractures and hydraulic fracturing fractures
The relationship between traditional seismic attributes and ant tracking attributes is closely related
It is mainly shown in the following two aspects
From the superimposed map with ant tracking and variance attribute (<a href="#F15">Figure 15</a>)
it was observed that there is a commonality between the abnormal values of variance attribute and ant tracking attribute
where the abnormal value of variance attribute is strong
the fractures detected by the ant tracking attribute appear to be more linear and sharper than those detected by the variance attribute
and the intersection relationship between the fractures is clearer
the number of fractures reflected by ant tracking is far greater than that detected by the variance attribute
Superimposed map of ant tracking slice and variance attribute along Longmaxi-Wufeng formation
One of the main limitations is the lack of a clear quantitative standard for scale division
The thresholds of ant tracking value were semi-quantitatively determined by the fracture morphology
which were used to further divide the fracture scales
there is no clear quantitative division standard
future research should focus on exploring clear quantitative standards for scale division
Another limitation of the ant tracking method is the lack of sufficient well data to calibrate and verify the accuracy
The accuracy of this method requires calibration and verification with more well data
otherwise there is a risk of false detection or misinterpretation of fracture patterns
it is more conducive to improving the accuracy of fracture predicting
A third limitation is the reliance on personal experience in completing the entire method
The completion of the entire method relies on the experience of geophysical researchers
which requires researchers to have a good understanding of seismic attributes and fracture morphology
the multi-scale fracture description method using seismic attributes was applied to predict and model multi-scale fractures in the study area
considering the varying impacts of fractures at different scales on drilling and completion engineering
it is necessary to identify a method to classify fractures at different scales
we utilized ant tracking values to classify fractures across multiple scales and subsequently performed multi-scale modeling
in order to classify fractures at different scales
we needed to identify a method with high prediction accuracy
we chose the ant tracking method for fracture prediction
Compared to fracture prediction using variance attribute
this method enhances the prediction accuracy of medium-small scale fractures and detects more fractures
compared to traditional single-group fracture modeling
this method divides fractures into four groups for separate fracture modeling
which is more aligned with engineering needs
(2) The strike of faults/fractures in the area primarily trends NW
with a small amount of nearly EW trending faults/fractures are also present
the NW-trending major faults run through the entire study area
With the NW-trending major faults as the boundary
NW and NE trending faults are primarily developed on the eastern side
and nearly EW and nearly NS trending faults are mainly developed on the western side
(3) This study has established a well-ordered and stepwise multi-scale refined fracture description process
the traditional seismic attributes were utilized to identify large-scale faults and establish a macro structural understanding
the ant tracking attribute was utilized to track and identify relatively small-scale faults/fractures
rendering faults/fractures more linear and precise
the ant tracking attribute values were grouped into four categories
and the discrete fracture modeling was carried out by multi-scale
(4) An improved ant tracking method based on frequency-filtering seismic data was proposed to enhance the accuracy of fracture detection
This method allowed for the detection of more continuous
and smaller-scale fractures compared to those detected using traditional full-band seismic data
The original contributions presented in the study are included in the article/Supplementary material
Supported by Fujian Provincial Natural Science Foundation of China (NO
2023J05053) and Research Initiation Fund of Fujian University of Technology (No
and JW were employed by Schlumberger China
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Application of small-scale curvature in small and micro-structure interpretation of coal field
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Quantitative prediction to fractured reservoir in buried hill based on pre-stack amplitude azimuthal anisotropy
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Some progress in reservoir fracture stochastic modeling research
doi:10.13810/j.cnki.issn.1000-7210.2018.03.023
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Automatic seismic image segmentation by introducing a novel strategy in histogram of oriented gradients
<a href="https://doi.org/10.1016/j.petrol.2021.109971">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Automatic+seismic+image+segmentation+by+introducing+a+novel+strategy+in+histogram+of+oriented+gradients&amp;btnG=">Google Scholar</a>
The application of frequency division ant tracking based on synchronous extrusion improvement of short time Fourier transform in crack detection
<a href="https://doi.org/10.11720/wtyht.2021.1022">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+application+of+frequency+division+ant+tracking+based+on+synchronous+extrusion+improvement+of+short+time+Fourier+transform+in+crack+detection&amp;btnG=">Google Scholar</a>
Seismic techniques for predicting fractures in granite buried hills
doi:10.13810/j.cnki.issn.1000-7210.2020.03.026
<a href="https://doi.org/10.13810/j.cnki.issn.1000-7210.2020.03.026">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Seismic+techniques+for+predicting+fractures+in+granite+buried+hills&amp;btnG=">Google Scholar</a>
Target-Oriented fusion of attributes in data level for salt dome geobody delineation in seismic data
<a href="https://doi.org/10.1007/s11053-022-10086-z">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Target-Oriented+fusion+of+attributes+in+data+level+for+salt+dome+geobody+delineation+in+seismic+data&amp;btnG=">Google Scholar</a>
Seismic coherence for discontinuity interpretation
<a href="https://doi.org/10.1007/s10712-021-09670-4">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Seismic+coherence+for+discontinuity+interpretation&amp;btnG=">Google Scholar</a>
Seismic attributes fusion and its research in predicting thickness of coal
<a href="https://doi.org/10.6038/pg20170521">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Seismic+attributes+fusion+and+its+research+in+predicting+thickness+of+coal&amp;btnG=">Google Scholar</a>
Micro-pore structure and fractal characteristics of deep shale from Wufeng formation to Longmaxi formation in jingmen exploration area
<a href="https://doi.org/10.11764/j.issn.1672-1926.2021.11.011">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Micro-pore+structure+and+fractal+characteristics+of+deep+shale+from+Wufeng+formation+to+Longmaxi+formation+in+jingmen+exploration+area,+hubei+province&amp;btnG=">Google Scholar</a>
Poststack seismic prediction techniques for fractures of different scales
<a href="https://doi.org/10.3969/j.issn.1000-1441.2019.05.016">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Poststack+seismic+prediction+techniques+for+fractures+of+different+scales&amp;btnG=">Google Scholar</a>
Application of edge detection technology in sand connectivity research
<a href="https://doi.org/10.6038/pg2022EE0330">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Application+of+edge+detection+technology+in+sand+connectivity+research&amp;btnG=">Google Scholar</a>
Seismic prediction of natural fractures in series of shale oil reservoirs
<a href="https://doi.org/10.3969/j.issn.1000-1441.2018.04.016">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Seismic+prediction+of+natural+fractures+in+series+of+shale+oil+reservoirs&amp;btnG=">Google Scholar</a>
Accurate boundary recognition research of central volcanic conduit: an example from Bohai A oilfield
<a href="https://doi.org/10.6038/pg2019BB0362">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Accurate+boundary+recognition+research+of+central+volcanic+conduit:+an+example+from+Bohai+A+oilfield&amp;btnG=">Google Scholar</a>
Characterization methods of multi-scale natural fractures in tight and low- permeability sandstone reservoirs
<a href="https://doi.org/10.16509/j.georeview.2021.02.020">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Characterization+methods+of+multi-scale+natural+fractures+in+tight+and+low-+permeability+sandstone+reservoirs&amp;btnG=">Google Scholar</a>
Application of an ant-tracking technique based on spectral decomposition to fault characterization
<a href="https://doi.org/10.3969/j.issn.1000-1441.2020.02.012">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Application+of+an+ant-tracking+technique+based+on+spectral+decomposition+to+fault+characterization&amp;btnG=">Google Scholar</a>
Fault enhancement in seismic images by introducing a novel strategy integrating attributes and image analysis techniques
<a href="https://doi.org/10.1007/s00024-022-03014-y">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Fault+enhancement+in+seismic+images+by+introducing+a+novel+strategy+integrating+attributes+and+image+analysis+techniques&amp;btnG=">Google Scholar</a>
<a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Reservoir+fracture+prediction&amp;btnG=">Google Scholar</a>
subsurface structures and tectonic features of the tuaheni landslide complex in the northern hikurangi margin
<a href="https://doi.org/10.3390/jmse11071359">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Gas+hydrates,+subsurface+structures+and+tectonic+features+of+the+tuaheni+landslide+complex+in+the+northern+hikurangi+margin,+New+Zealand,+revealed+by+seismic+attribute+analysis&amp;btnG=">Google Scholar</a>
<a href="https://doi.org/10.1190/geo2017-0196.1">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Multi+azimuth+coherence&amp;btnG=">Google Scholar</a>
Analysis of seismic scale fracture system of shale reservoir and its petroleum significance: a case study of well Ning 201area of Changning Block
<a href="https://doi.org/10.3969/j.issn.1672-9854.2019.04.009">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Analysis+of+seismic+scale+fracture+system+of+shale+reservoir+and+its+petroleum+significance:+a+case+study+of+well+Ning+201area+of+Changning+Block,+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Countermeasures to promote the development of China&#x02019;s shale gas industry
<a href="https://doi.org/10.12075/j.issn.1004-4051.2018.08.025">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Countermeasures+to+promote+the+development+of+China’s+shale+gas+industry&amp;btnG=">Google Scholar</a>
Vertical heterogeneity and the main controlling factors of the upper ordovician-lower silurian wufeng-longmaxi shales in the middle Yangtze region
<a href="https://doi.org/10.19509/j.cnki.dzkq.2021.0053">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Vertical+heterogeneity+and+the+main+controlling+factors+of+the+upper+ordovician-lower+silurian+wufeng-longmaxi+shales+in+the+middle+Yangtze+region&amp;btnG=">Google Scholar</a>
Application of multi&#x02043;attribute fusion in quantitative prediction of reservoirs: a case study of Yangshuiwu buried hill in Langgu sag
<a href="https://doi.org/10.11720/wtyht.2022.2371">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Application+of+multi⁃attribute+fusion+in+quantitative+prediction+of+reservoirs:+a+case+study+of+Yangshuiwu+buried+hill+in+Langgu+sag&amp;btnG=">Google Scholar</a>
Seepage characteristic and fracture development of protected seam caused by mining protecting strata
doi:10.13532/j.jmsce.cn10-1638/td.20201215.001
<a href="https://doi.org/10.13532/j.jmsce.cn10-1638/td.20201215.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Seepage+characteristic+and+fracture+development+of+protected+seam+caused+by+mining+protecting+strata&amp;btnG=">Google Scholar</a>
Wide-azimuth Young&#x02019;s modulus inversion and fracture prediction: an example of H structure in Bozhong sag
doi:10.13810/j.cnki.issn.1000-7210.2021.03.018
<a href="https://doi.org/10.13810/j.cnki.issn.1000-7210.2021.03.018">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Wide-azimuth+Young’s+modulus+inversion+and+fracture+prediction:+an+example+of+H+structure+in+Bozhong+sag&amp;btnG=">Google Scholar</a>
Evaluation of fracture belts and optimization of borehole tracks in carbonate formations through information fusion of seismic attributes and electric image well logging
<a href="https://doi.org/10.13278/j.cnki.jjuese.20200007">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Evaluation+of+fracture+belts+and+optimization+of+borehole+tracks+in+carbonate+formations+through+information+fusion+of+seismic+attributes+and+electric+image+well+logging&amp;btnG=">Google Scholar</a>
Seismic prediction method of multiscale fractured reservoir
<a href="https://doi.org/10.1007/s11770-018-0667-8">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Seismic+prediction+method+of+multiscale+fractured+reservoir&amp;btnG=">Google Scholar</a>
Application of frequency division ant tracking technology Based on Sparse Bayesian in fracture characterization
<a href="https://doi.org/10.3969/j.issn.1001-1749.2023.02.08">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Application+of+frequency+division+ant+tracking+technology+Based+on+Sparse+Bayesian+in+fracture+characterization&amp;btnG=">Google Scholar</a>
Research methods of different levels of reservoirs based on seismic data
<a href="https://doi.org/10.11648/j.earth.20200902.12">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Research+methods+of+different+levels+of+reservoirs+based+on+seismic+data&amp;btnG=">Google Scholar</a>
Geoscience-to-production integration ensures effective and efficient south China marine shale gas development
<a href="https://doi.org/10.3969/j.issn.1672-7703.2015.04.001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geoscience-to-production+integration+ensures+effective+and+efficient+south+China+marine+shale+gas+development&amp;btnG=">Google Scholar</a>
Application study of improving the precision of the ant-tracking-based fracture prediction technique
<a href="https://doi.org/10.11720/wtyht.2021.1208">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Application+study+of+improving+the+precision+of+the+ant-tracking-based+fracture+prediction+technique&amp;btnG=">Google Scholar</a>
An improved ant-tracking workflow based on divided-frequency data for fracture detection
<a href="https://doi.org/10.1093/jge/gxac075">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=An+improved+ant-tracking+workflow+based+on+divided-frequency+data+for+fracture+detection&amp;btnG=">Google Scholar</a>
Geological characteristics of Longmaxi formation shale reservoir and &#x0201c;sweet spot layers&#x0201d; optimization in Jingmen area
<a href="https://doi.org/10.3969/j.issn.2095-8471.2020.05.005">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geological+characteristics+of+Longmaxi+formation+shale+reservoir+and+sweet+spot+layers+optimization+in+Jingmen+area&amp;btnG=">Google Scholar</a>
Structural deformation characteristics and shale gas preservation conditions in the zhaotong national shale gas demonstration area along the southern margin of the sichuan basin
<a href="https://doi.org/10.3787/j.issn.1000-0976.2019.10.003">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Structural+deformation+characteristics+and+shale+gas+preservation+conditions+in+the+zhaotong+national+shale+gas+demonstration+area+along+the+southern+margin+of+the+sichuan+basin&amp;btnG=">Google Scholar</a>
The calculation method of curvature attributes and its effect analysis
<a href="https://doi.org/10.1190/segam2015-5853793.1">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+calculation+method+of+curvature+attributes+and+its+effect+analysis&amp;btnG=">Google Scholar</a>
An integrating technology of ant tracking and frequency division and its application to interpretation on low-order fault: examples from Xujiahe tight sandstone gas reservoirs
doi:10.12055/gaskk.issn.1673-3177.2021.04.013
<a href="https://doi.org/10.12055/gaskk.issn.1673-3177.2021.04.013">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=An+integrating+technology+of+ant+tracking+and+frequency+division+and+its+application+to+interpretation+on+low-order+fault:+examples+from+Xujiahe+tight+sandstone+gas+reservoirs,+Zhongtaishan+area,+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Review on optimization and fusion of seismic attributes: for fluvial reservoir characterization
<a href="https://doi.org/10.3799/dqkx.2022.221">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Review+on+optimization+and+fusion+of+seismic+attributes:+for+fluvial+reservoir+characterization&amp;btnG=">Google Scholar</a>
The effect of multi-scale faults and fractures on oil enrichment and production in tight sandstone reservoirs: a case study in the southwestern ordos basin
<a href="https://doi.org/10.3389/feart.2021.664629">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+effect+of+multi-scale+faults+and+fractures+on+oil+enrichment+and+production+in+tight+sandstone+reservoirs:+a+case+study+in+the+southwestern+ordos+basin,+China&amp;btnG=">Google Scholar</a>
Image edge detection algorithm and its new development
<a href="https://doi.org/10.3778/j.issn.1002-8331.1804-0205">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Image+edge+detection+algorithm+and+its+new+development&amp;btnG=">Google Scholar</a>
Geological characteristics of shale gas reservoir in Yichang area
<a href="https://doi.org/10.7623/syxb201908001">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Geological+characteristics+of+shale+gas+reservoir+in+Yichang+area,+western+Hubei&amp;btnG=">Google Scholar</a>
Application of curvature attributes to fluvial reservoirs discontinuity detection
Geophysical and Geochemical Exploration 45 (2)
<a href="https://doi.org/10.11720/wtyht.2021.1079">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Application+of+curvature+attributes+to+fluvial+reservoirs+discontinuity+detection&amp;btnG=">Google Scholar</a>
The fracture modeling in the constraint of ant tracking attribute
Journal of Yangtze University (Natural Science Edition) 13 (14)
doi:10.3969/j.issn.1673-1409(s).2016.14.004
<a href="https://doi.org/10.3969/j.issn.1673-1409(s).2016.14.004">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=The+fracture+modeling+in+the+constraint+of+ant+tracking+attribute&amp;btnG=">Google Scholar</a>
Classified-staged-grouped 3D modeling of multi-scale fractures constrained by genetic mechanisms and main controlling factors: a case study on biohermal carbonate reservoir of the Upper Permian Changxing Fm
<a href="https://doi.org/10.11743/ogg20230118">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Classified-staged-grouped+3D+modeling+of+multi-scale+fractures+constrained+by+genetic+mechanisms+and+main+controlling+factors:+a+case+study+on+biohermal+carbonate+reservoir+of+the+Upper+Permian+Changxing+Fm.+in+Yuanba+area,+Sichuan+Basin&amp;btnG=">Google Scholar</a>
Multi-scale analysis technique based on curvelet transform
<a href="https://doi.org/10.3321/j.issn:1000-7210.2009.05.004">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Multi-scale+analysis+technique+based+on+curvelet+transform&amp;btnG=">Google Scholar</a>
Exploration and development prospects of shale gas resources: a case study of Sichuan Basin 44 (10)
<a href="https://doi.org/10.19389/j.cnki.1003-0506.2022.10.020">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Exploration+and+development+prospects+of+shale+gas+resources:+a+case+study+of+Sichuan+Basin&amp;btnG=">Google Scholar</a>
A joint inversion method using amplitude and velocity anisotropy
doi:10.13810/j.cnki.issn.1000-7210.2020.05.016
<a href="https://doi.org/10.13810/j.cnki.issn.1000-7210.2020.05.016">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=A+joint+inversion+method+using+amplitude+and+velocity+anisotropy&amp;btnG=">Google Scholar</a>
Improved ant tracking crack detection algorithm and its application
<a href="https://doi.org/10.3969/j.issn.1008-2336.2019.03.027">CrossRef Full Text</a> &#x0007c; <a href="https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Improved+ant+tracking+crack+detection+algorithm+and+its+application&amp;btnG=">Google Scholar</a>
Guan S and Wang J (2024) Application of seismic attribute analysis techniques to multi-scale natural fractures description: a case study of the Longmaxi-Wufeng formation in H shale gas block
Received: 26 December 2023; Accepted: 08 April 2024;Published: 03 May 2024
Copyright &#x000a9; 2024 Xie, Chen, Zhao, Li, Guan and Wang. This is an open-access article distributed under the terms of the <a rel="license" href="http://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution License (CC BY).</a> The use
&#x0002a;Correspondence: Qinghui Xie, <a id="encmail">cWluZ2h1aXhpZUBzaW5hLmNvbQ==</a>
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As China's millennial generation and people born after 2000 grow up and start to play an increasingly important role in Chinese society
the government and the Party are harnessing pop idols
Internet slang and new media to attract a younger following
This has also prompted musicians to pen modern versions of revolutionary "red songs."
A screenshot of the animated rap video "Four Comprehensives," produced by the Xinhua News Agency
Catchy jingles, a jumping cartoon version of President <a href="http://www.globaltimes.cn/db/profiles/xijinping.shtml" target="_blank">Xi Jinping</a>
and middle-aged man rapping about China's latest development plans are just a few ways the government is promoting its policies and national ideology.An animated rap video produced by the Xinhua News Agency
a list of political goals for China advocated by President Xi
a man explains the goals to a girl as they rap and boogie to an upbeat tune.Since late 2013
patriotic pop songs and micro films appeared on China's social media platforms such as Weibo and WeChat
with themes ranging from publicizing government plans to lauding the country's prosperity
These are not the only attempts the Chinese government has made in recent years to harness pop culture for its goals
The Central Committee of the China Communist Youth League (CCYL)
comics and mobile games to recruit members
and has invited boy band TFboys to become its ambassadors."China's millennial generation grew up with the Internet
Youngsters born after 2000 have an even greater dependence on the Internet
The Party and the central government is hoping to approach and influence these younger generations using their favorite forms such as animation," said He Hui
professor at the School of International Journalism and Communication
Pop band TFboys wear red scarves in a CCYL video
Blurred backgroundThe On Fuxing Road Studio was the first studio to use animation to promote government policies when it launched a 5-minute video explaining how Chinese leaders are chosen in October 2013
Of the seven videos it has released so far
three are about policymaking and the achievements of the Communist Party of China (CPC)
The most recent one is "Shisanwu," an animated video which explains the government's 13th Five-Year Plan through a folk song performed in English by foreigners.A spokesperson for On Fuxing Road Studio
attributed their attempts to China's development and President Xi Jinping's call for more diversified methods of overseas publicity in 2013."If China had not been at this stage of development
If our national leaders hadn't been encouraging these efforts
this won't be possible either," she told the Global Times in a telephone interview.Although the On Fuxing Road Studio has not revealed its real identity
the capital's video production professionals believe it has official background.The name of the studio itself is revealing - Fuxing Road
part of the extended Chang'an Avenue in west Beijing
is home to many ministries and government organizations such as the International Department of the Central Committee of the CPC.Professor He said that since the Party and the government are still experimenting with these new forms
it's understandable that it wants to publish the videos through an ostensibly grass-roots organization to test the waters."Playing down its official background can also make the videos more amiable and acceptable
one-way Chinese publicity which is often too explicit and political," he told the Global Times
Successors of communismAnimation and rap videos are not the only way the government is trying to attract a younger following
is using young pop idols to unite its members - virtually all Chinese aged between 14 and 28.Last June
it invited boy band TFboys and popular singer Han Geng to cover "We are the Successors of Communism," a song written in 1961 which later became the anthem of the CCYL
TFboys are the hottest pop band in China today
consisting of three young men born in 1999 and 2000
each with over 13 million followers on Sina Weibo
while Han Geng is a South Korea-trained Chinese pop singer
Statistics show that most of their fans are under 30 years old.The song's music video was produced by Rao Jin
the Tsinghua graduate known for establishing Anti-CNN.com in 2008
a site which attempts to refute what Rao sees as false Western media reports about China
are shown putting on red scarves and raising their hands in a salute
Basketball player-turned-entrepreneur Yao Ming and other famous personalities also appeared in the video.After the CCYL Central Committee posted the video on its Weibo
making it the most popular Weibo post in the committee's history."If we use the proper youth idols in a proper way
we can help young people build a correct world view," Wu Dezu
director of the new media division at the CCYL Central Committee
said in an interview on CCYL's WeChat account.Wu also revealed that CCYL's new media division was established at the end of 2013
"What we want to do is to spread positive energy in this age of new media
and present them fashionably," he said in the interview.The song and video were not the only cooperation between the young idols and the CCYL
the organization invited TFboys to join its mobilizing meeting that asks young people to comment rationally and positively on the Internet and help create a "healthy online environment," where the three young men recited a manifesto on that theme.In addition to the use of idols
comics and Internet slang are used by the CCYL to try to keep up with the younger generation.The CCYL's Hainan committee
last November launched a mobile game that quizzes players about the "socialist core values," a dozen words promoted by the government including patriotism
the Weibo of the CCYL's school department published a comic entitled "I like how you pursue me while reciting socialist core values," about how a girl is impressed by her suitor's ability to recite the terms and then falls in love with him
Stuffed full of Internet slang and drawn in the style of Japanese manga
the post was another obvious example of how the CYLC is changing its style to draw in young followers.Modern red songsThe production and popularity of some of these songs and cartoons have spurred the creative spirit of nationalistic grass-roots singers and songwriters.In the past two years
the popularity of songs lauding the country and its achievements have been on the rise
taking a variety of forms.On music streaming site QQ Music
over 10 different songs have President Xi Jinping's nickname "Xi Dada" in their titles
with styles ranging from folk songs to disco
Most of these songs praise President Xi's anti-corruption campaigns and his personal style.One of these grass-roots patriotic songwriters is Wufeng Jifeng
a singer-songwriter based in South China's Guangdong Province
who recently wrote a song entitled "As you wished," dedicated to former Chinese Premier Zhou Enlai and praising China's prosperity.Wufeng calls himself a ziganwu
or self-motivated Internet commenter who defends the government
and said his song is a modern spin on traditional red songs dedicated to revolutionary leaders."Traditional red songs belong to the past century
and now a more down-to-earth method is needed to express that same spirit
This is why I used rock music to interpret it," he told the Global Times.The title and lyrics of the song's chorus were inspired by one netizen's famous comment after China's massive military parade last September in WWII commemoration
who uses the moniker "Zhou Gubei Dezhou," posted a picture of former Chinese Premier Zhou Enlai and commented
"This age of prosperity is as you wished." That post was shared over 920,000 times.Unlike most rock songs
Wufeng's song rejects rebellion in favor of conformity
"Through this song I want to show collectivism and how common people are moved [by the country's achievement]," he said
He wrote the lyrics with his cyber friend Cui Zijian
who in real life is a CPC publicity officer in the Bortala Mongol Autonomous Prefecture
Xinjiang Uyghur Autonomous Region."Animated songs [like "Shisanwu"] are very good attempts to approach the masses
but we cannot let the central government do everything
Grass-roots participation is equally important," Cui told the Global Times.After a version of the song was uploaded on Weibo
it grabbed the attention of the Central Committee of the Communist Youth League of China
whose official Weibo account reposted the song
3128TAIPEI (Taiwan News) &mdash; Taiwanese-Turkish TV show host Ugur Rifat Karlova
on Tuesday (March 22) became the first foreign-born entertainer to receive a Ministry of Foreign Affairs (MOFA) press card
Karlova, who in 2018 completed <a href="https://www.taiwannews.com.tw/en/news/3392076">the process</a> of becoming a <a href="https://www.taiwannews.com.tw/en/news/3387788">Taiwanese citizen</a>
told Taiwan News that Turkey&#39;s İhlas News Agency (IHA) had been searching for a reporter in Taiwan for quite some time and that another journalist had recommended him as a strong candidate
The news agency found Karlova to be a good fit based on his language skills and work in TV broadcasting and hired him to serve as their official Taiwan foreign correspondent on Feb
IHA sent a letter to MOFA requesting the necessary accreditation for Karlova to file reports on behalf of the agency
&nbsp;MOFA approved IHA&#39;s request on March 17 and on Tuesday
director general of the Department of International Information Services
formally handed Karlova his MOFA press card
Karlova said that through his reports for IHA
which will be distributed across media platforms such as the newspaper H&uuml;rriyet
he will be able to reach many of the approximately 80 million Turkish speakers around the world
he is the first and only foreigner in Taiwan&#39;s entertainment industry who has received the MOFA press ID
As an IHA reporter, he has already covered a wide range of topics such as the <a href="https://www.milliyet.com.tr/galeri/9-gun-surecek-tayvanda-geleneksel-fener-festivali-basladi-6699117/1" target="_blank">Taiwan Lantern Festival</a>
Omicron vaccine research by Academia Sinica
and the debate on lengthening Taiwan&#39;s mandatory conscription period
He said that he is very pleased to have this opportunity to cover a wide range of subjects
to enable the world to better understand Taiwan
Wu Feng (left) holds envelope containing MOFA press card with Hsu
Taiwan rail union mulls strike vote in protest against vouchers
Yunlin invites public to National Day fireworks rehearsal in central Taiwan
Taiwan to simulate impact of magnitude 7.3 earthquake
Pilot who ejected from Taiwan fighter jet recovering well
Taiwan dollar hits NT$29 per US dollar triggering currency exchange rush
Taipei MRT reminds passengers of drinking water ban
Magnitude 5.5 earthquake strikes off east Taiwan
Vietjet flight makes unscheduled landing in Taiwan
Four Vietnamese residents found dead in northern Taiwan
Central Bank steps in as Taiwan dollar posts strong single-day gain
Taiwan ranked 2nd most innovative country in world
Rising Taiwan dollar over Trump tariffs has pros and cons
US tech earnings spark Taiwan stock market rally
Taiwan ranks 1st in Asia on World Press Freedom Index
The Water and Soil Conservation Bureau issued 72 red-alert warnings for landslides and rockfalls in northern districts of Taiwan as heavy rain generated by Typhoon In-Fa continues to inundate the area
Heavy rain began to pound northern Taiwan from Wednesday evening as the tropical storm approached the area
only to stop and hover over the Yaeyama Islands for two days before finally moving away in a north-northwest direction
While the Central Weather Bureau lifted the sea warning for Typhoon In-Fa at 11:30 am this morning
based on the wind and rain data of the CWB
the Bureau of Soil and Water Conservation issued 72 soil and rock flow red alerts for 23 villages and 6 townships in Hsinchu County
45 yellow-alert warnings were issued in the same counties and cities
Multiple landslides blocked parts of route 122 in Hsinchu County&#8217;s Wufeng Township this morning
and 42.8 kilometer marks were quickly dealt with and cleared
a larger landslip has almost completely blocked the road at the 31.5 kilometer mark
According to the Wufeng Township office only scooters can get through
The New Taipei City Fire Department said as of 10:00 am today it has received 83 reports related to the weather including 8 cases of flooding
In Miaoli County a 44-year-old woman narrowly escaped serious injury when part of a tree trunk speared the front windshield of her car on the Wuhu Village section of route 119 yesterday afternoon
Ms Wu suffered minor abrasions but was otherwise unharmed
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Taiwan English News is published by <a href="http://www.athertontablelandnetguide.com/netguide/network/">Phillip Charlier</a> who is based in New Taipei City, Taiwan.  If you have news tips or issues you want covered: <a href="https://taiwanenglishnews.com/contact-taiwan-english-news/">Let me know</a>