Simulation of coalbed methane generation, dissipation, and preservation and analysis of the geological influencing factors: a case study of the Xinjing coal mine, northeastern Qinshui basin, China

The Xinjing coal mine is a favorable block for coalbed methane (CBM) exploitation in China because of the high gas content of coal seams. To better understand the dynamic evolution process of CBM in this area, the CBM generation, dissipation, and preservation of the No. 3 and 15 coal seams were simulated based on the restoration of tectonic evolution history, sedimentary burial history, and thermal history. The evolution characteristics of CBM and the main geological influencing factors in each evolution stage were discussed as well. The results show that the dynamic evolution process of CBM can be divided into six stages: the immature biogenic gas generation stage; the primary gas generation stage; the slow gas generation stage; the secondary gas generation stage; the absolute slowly gas dissipation stage; and the absolute sharply gas dissipation stage. Moreover, the regional tectonic movement was the most significant factor controlling the whole CBM evolution, and there were also other geological factors such as coal thickness, burial depth, and coal mine structures that significantly affected the CBM evolution during different tectonic periods. During the Indosinian period, coal thickness and burial depth controlled the CBM evolution process while in the Yanshanian and Himalayan periods, the CBM evolution was the comprehensive result of the factors like coal thickness, burial depth, and coal mine structures.