| Citation: |
Shu-jing Bao, Tian-xu Guo, Jin-tao Yin, Wei-bin Liu, Sheng-jian Wang, Hao-han Li, Zhi Zhou, Shi-zhen Li, Xiang-lin Chen, 2024. Geological conditions and reservoir characteristics of various shales in major shale-hosted regions of China, China Geology, 7, 138-149. doi: 10.31035/cg2022082
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Geological conditions and reservoir characteristics of various shales in major shale-hosted regions of China
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Abstract
China is home to shales of three facies: Marine shale, continental shale, and marine-continental transitional shale. Different types of shale gas are associated with significantly different formation conditions and major controlling factors. This study compared the geological characteristics of various shales and analyzed the influences of different parameters on the formation and accumulation of shale gas. In general, shales in China’s several regions exhibit high total organic carbon (TOC) contents, which lays a sound material basis for shale gas generation. Marine strata generally show high degrees of thermal evolution. In contrast, continental shales manifest low degrees of thermal evolution, necessitating focusing on areas with relatively high degrees of thermal evolution in the process of shale gas surveys for these shales. The shales of the Wufeng and Silurian formations constitute the most favorable shale gas reservoirs since they exhibit the highest porosity among the three types of shales. These shales are followed by those in the Niutitang and Longtan formations. In contrast, the shales of the Doushantuo, Yanchang, and Qingshankou formations manifest low porosities. Furthermore, the shales of the Wufeng and Longmaxi formations exhibit high brittle mineral contents. Despite a low siliceous mineral content, the shales of the Doushantuo Formation feature a high carbonate mineral content, which can increase the shales’ brittleness to some extent. For marine-continental transitional shales, where thin interbeds of tight sandstone with unequal thicknesses are generally found, it is recommended that fracturing combined with drainage of multiple sets of lithologic strata should be employed to enhance their shale gas production.
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Shu-jing Bao, Tian-xu Guo, Jin-tao Yin, Wei-bin Liu, Sheng-jian Wang, Hao-han Li, Zhi Zhou, Shi-zhen Li, Xiang-lin Chen, 2024. Geological conditions and reservoir characteristics of various shales in major shale-hosted regions of China, China Geology, 7, 138-149. doi: 10.31035/cg2022082
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Figure 1.
Geographical location map of the study area.
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Figure 2.
TOC (a), Ro (b), porosity (c), and Brittle mineral (d) features of different types of shales. DST Fm.‒Doushantuo Formation; NTT Fm.‒Niutitang Formation; LMX Fm.‒Longmaxi Formation; LT Fm.‒Longtan Formation; YC Fm.‒Yanchang Formation; QSK Fm.‒Qingshankou Formation.
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Figure 3.
SEM photos show the different pore types. a‒dissolved pores in Doushantuo shale; b‒organic pores in Doushantuo shale; c‒shrinkage joints between organic matter and mineral particles in Niutitang shale; d‒strawberry-shaped pyrite aggregates and intercrystalline filling of organic pores in organic matter in Niutitang shale; e‒mass organic matter and internal organic pores in Longmaxi shale; f‒strawberry-shaped pyrite aggregates and intercrystalline filling of organic pores in organic matter in Longmaxi shale; g‒organic pores in Longtan shale; h‒strawberry-shaped pyrite intercrystalline pores in Longtan shale; i‒intergranular pores between clay minerals and detrital particles in Yanchang shale; g‒spongy organic pores in Yanchang shale; k‒intercrystalline pores in clay minerals in Qingshankou shale; l‒intercrystalline pores in pyrite Qingshankou shale.
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Figure 4.
Triangle diagram of the mineral content of different types of shale. The legend abbreviations are the same as in Fig. 2.
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Figure 5.
Relationship between TOC and total gas content.
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Figure 6.
Relationship of Vitrinite reflectance (Ro) to porosity and total gas content.
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Figure 7.
Relationship between porosity and TOC. Part of the data comes from Xiao XM et al., 2015; Qiao H et al., 2018; Deng J et al., 2018.
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Figure 8.
Relationship between porosity and TOC. The data on Yanchang shale come from Li XJ et al., 2017.
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Figure 9.
Relationship between porosity and total gas content. Part of the data comes from Qiao H et al., 2018; Guo XS et al., 2016. Data from Permian and Jurassic shale were derived from log interpretation.