Effects of coal permeability rebound and recovery phenomenon on CO2 storage capacity under different coalbed temperature conditions during CO2-ECBM process

During the permeability evolution process, coal permeability rebound and recovery is an important behaviour. Currently, studies on it mainly focus on the effects of reservoir pressure changes, but the influence of temperature is also significant. In the study, a binary gas permeability evolution model was constructed, which considers the competition mechanism between effective stress, gas adsorption/desorption, and thermal expansion. The model was employed to study the dynamic evolution of various parameters during CO2 injection into CH4-containing coal at different temperatures. The findings demonstrate a complex permeability evolution over time, characterized by a rapid decrease followed by a significant increase and then another gradual decrease. And the time required for permeability rebound and recovery increases as the temperature increases. Moreover, by monitoring the law of gas migration at fixed points and other methods to obtain the changing trend of CO2 flow rate and CO2 cumulative storage volume on a time scale. The results showed that both CO2 flow rate and CO2 cumulative storage volume decreased with increased permeability rebound and recovery time. Inspired by the abovementioned laws, this study proposed using the stage-pressure injection method in high-temperature coal. Results indicate that the stage-pressure method can increase the CO2 injection effect.