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Abstract

AAPG Bulletin, V. 106, No. 2 (February 2022), P. 387-407.

Copyright ©2022. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/09152120028

Indication of origin and distribution of coalbed gas from stable isotopes of gas and coproduced water in Fukang area of Junggar Basin, China

Qiong Wang,1 Hao Xu,2 Dazhen Tang,3 Shuguang Yang,4 Gang Wang,5 Pengfei Ren,6 Wenyang Dong,7 and Jingzhen Guo8

1School of Energy Resources, China University of Geosciences (Beijing), Beijing, China; Coal Reservoir Laboratory of National Engineering Research Center of Coalbed Methane (CBM) Development & Utilization, China University of Geosciences, Beijing, China; Beijing Key Laboratory of Unconventional Natural Gas Geological Evaluation and Development Engineering, Beijing, China; [email protected]
2School of Energy Resources, China University of Geosciences (Beijing), Beijing, China; Coal Reservoir Laboratory of National Engineering Research Center of CBM Development & Utilization, China University of Geosciences, Beijing, China; Beijing Key Laboratory of Unconventional Natural Gas Geological Evaluation and Development Engineering, Beijing, China; [email protected]
3School of Energy Resources, China University of Geosciences (Beijing), Beijing, China; Coal Reservoir Laboratory of National Engineering Research Center of CBM Development & Utilization, China University of Geosciences, Beijing, China; Beijing Key Laboratory of Unconventional Natural Gas Geological Evaluation and Development Engineering, Beijing, China; [email protected]
4CBM Research & Development Center, Xinjiang Coal Field Geology Bureau, Urumqi, Xinjiang, China; [email protected]
5CBM Research & Development Center, Xinjiang Coal Field Geology Bureau, Urumqi, Xinjiang, China; [email protected]
6State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, Sichuan, China; [email protected]
7School of Energy Resources, China University of Geosciences (Beijing), Beijing, China; Coal Reservoir Laboratory of National Engineering Research Center of CBM Development & Utilization, China University of Geosciences, Beijing, China; Beijing Key Laboratory of Unconventional Natural Gas Geological Evaluation and Development Engineering, Beijing, China; [email protected]
8School of Energy Resources, China University of Geosciences (Beijing), Beijing, China; Coal Reservoir Laboratory of National Engineering Research Center of CBM Development & Utilization, China University of Geosciences, Beijing, China; Beijing Key Laboratory of Unconventional Natural Gas Geological Evaluation and Development Engineering, Beijing, China; [email protected]

ABSTRACT

The Junggar Basin is rich in low-rank coalbed gas resources. This paper uses the stable isotopes of gas and coproduced water to analyze the origin and distribution of coalbed gas in the Lower Jurassic Badaowan Formation in the Fukang area of southern Junggar Basin, China. In this work, it was found that microbial gas is mainly present at depths ≤800 m where the temperature and total dissolved solids were suitable for methanogen gas production. Thermogenic gas is primarily present at buried depths greater than 1000 m where the coal seam has a higher degree of thermal evolution, and a mixture of the two was present at buried depths of 800–1000 m. Thermogenic gas accounts for 40.1% to 41.7%. Microbial gas accounts for the remaining 58.3% to 59.9% and is generated mainly by CO2 reduction. A fraction of microbial gas is likely produced via acetate fermentation on the eastern and western sides. High gas contents are confined to permeable coal seams where microbial activity continues, that is, at depth of 600–1000 m. The extensive biological effects from Mesozoic to present day have resulted in the extremely heavy δ13C-CO2 values. Na-HCO3-Cl–type water and high total dissolved solids indicate that the study area is distal to the recharge zone. Strong water evaporation in the study area leads the hydrogen and oxygen isotopes of formation water to deviate to the right of the global meteoric water line.

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