Effect of CO2 injection on Coalbed Permeability Based on a Thermal–Hydraulic–Mechanical Coupling Model

The permeability of coal seam is an important parameter that affects the production of coalbed methane and the storage of CO2. Therefore, it is of great significance to elucidate the evolution of permeability under different injection parameter conditions during enhanced coalbed methane recovery with CO2 sequestration (CO2-ECBM). In this study, a fully coupled mathematical model of thermal–hydraulic–mechanical (THM) in the CO2-ECBM process was established first. Moreover, the validity of the THM model developed in this paper was verified. Finally, the mechanism of influence of different CO2 injection conditions on the permeability of coal reservoirs and the implications of this study for the improvement of CO2-ECBM engineering were described. The results show that the higher the injection pressure, the lower the permeability, and the greater the range of permeability reduction caused by CO2 injection. Near the injection well, the higher the injection temperature, the lower the permeability. When the distance from the injection well is greater than 4 m, the higher the injection temperature, the higher the permeability. This may be related to the initial temperature of coal reservoir. This study not only provides theoretical support for improving the existing problems of lower injectivity and less than expected injectivity in the current CO2-ECBM field engineering but also promotes the realization of the global "carbon neutrality" goal.