Geological Constraints on the Gas-Bearing Properties in High-Rank Coal: A Case Study of the Upper Permian Longtan Formation from the Songzao Coalfield, Chongqing, Southwest China

Dishu Chen, Jinxi Wang, Xuesong Tian (), Dongxin Guo, Yuelei Zhang and Chunlin Zeng
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Dishu Chen: Key Laboratory of Shale Gas Exploration, Ministry of Natural Resources, Chongqing Institute of Geology and Mineral Resources, Chongqing 401120, China
Jinxi Wang: Key Laboratory of Shale Gas Exploration, Ministry of Natural Resources, Chongqing Institute of Geology and Mineral Resources, Chongqing 401120, China
Xuesong Tian: Key Laboratory of Shale Gas Exploration, Ministry of Natural Resources, Chongqing Institute of Geology and Mineral Resources, Chongqing 401120, China
Dongxin Guo: Key Laboratory of Shale Gas Exploration, Ministry of Natural Resources, Chongqing Institute of Geology and Mineral Resources, Chongqing 401120, China
Yuelei Zhang: Key Laboratory of Shale Gas Exploration, Ministry of Natural Resources, Chongqing Institute of Geology and Mineral Resources, Chongqing 401120, China
Chunlin Zeng: Key Laboratory of Shale Gas Exploration, Ministry of Natural Resources, Chongqing Institute of Geology and Mineral Resources, Chongqing 401120, China

Energies, 2024, vol. 17, issue 5, 1-22

Abstract: The Permian Longtan Formation in the Songzao coalfield, Southwest China, has abundant coalbed methane (CBM) stored in high-rank coals. However, few studies have been performed on the mechanism underlying the differences in CBM gas content in high-rank coal. This study focuses on the characterization of coal geochemical, reservoir physical, and gas-bearing properties in the coal seams M 6 , M 7 , M 8 , and M 12 based on the CBM wells and coal exploration boreholes, discusses the effects of depositional environment, tectono-thermal evolution, and regional geological structure associated with CBM, and identifies major geological constraints on the gas-bearing properties in high-rank coal. The results show that high-rank coals are characterized by high TOC contents (31.49~51.32 wt%), high T max and R 0 values (averaging 539 °C and 2.17%), low HI values (averaging 15.21 mg of HC/g TOC), high porosity and low permeability, and high gas-bearing contents, indicating a post-thermal maturity and a good CBM production potential. Changes in the shallow bay–tidal flat–lagoon environment triggered coal formation and provided the material basis for CBM generation. Multistage tectono-thermal evolution caused by the Emeishan mantle plume activity guaranteed the temperature and time for overmaturation and thermal metamorphism and added massive pyrolytic CBM, which improved the gas production potential. Good geological structural conditions, like enclosed fold regions, were shown to directly control CBM accumulation.

Keywords: coalbed methane enrichment; Permian Longtan Formation; high-rank coal; depositional environment; tectono-thermal evolution; regional geological structure (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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