Coupling Mechanism of THMC Fields in Crushed Soft Coal with Low Permeability after CO<sub>2</sub> Injection and Its Application in CO<sub>2</sub>-ECBM Technology
Huihuang Fang, Shua Yu, Shiwen Zhang, Shuxun Sang, Jinran Guo, Zhangfei Wang, Xicheng Wang
Abstract
During the CO 2 -ECBM process in crushed soft coal with low permeability (CSLP-Coal), the analysis of the fully coupled mechanism of the thermo-hydro-mechanical-chemical (THMC) fields is conducive to engineering promotion of CO 2 -ECBM technology. In this study, the CSLP-Coal in Huainan and Huaibei coalfields was taken as the research object; the fully coupled mathematical models of THMC fields were established; the effects of injection pressure, temperature, and initial permeability were studied; the evolution connotation of reservoir permeability was discussed; and the reaction mechanism of the chemical field was analyzed. The evaluation system of the CO 2 -ECBM project in CSLP-Coal was further established. The results show that the mathematical models of THMC fields are fully coupled during the CO 2 -ECBM process. Injection pressure, temperature, and initial permeability have great influence on the CO 2 -ECBM technology. The variation of reservoir permeability is mainly influenced by the effective stress effect and competitive adsorption effect of CH 4 /CO 2 . The formation of a geochemical reaction system with CH 4 /CO 2 -H 2 O-coal is conducive to the engineering popularization of the CO 2 -ECBM technology. Based on the three indexes, the evaluation system for the practical effectiveness of CO 2 -ECBM engineering in CSLP-Coal in Huainan and Huaibei coalfields can be constructed. This study has important theoretical and practical significance for improving the recovery efficiency of CH 4 and enhancing the ability of CO 2 storage in CSLP-Coal.