Sensitivity simulation and analysis of CO₂ injection for enhanced coalbed methane recovery

Injecting CO₂ into a coal seam with the purpose of enhancing desorption of coalbed methane can be applied to the long-term storage of CO ₂, which accompanies with complex coal gas interactions. In this study, a fully coupled coal deformation, gas flow, CH₄-CO₂ counter-diffusion and gas absorption/desorption finite element (FE) model was developed to investigate sensitivity of CO₂ injection related parameters. Modeling results indicate that (1) CO₂ injectivity is positively sensitive to injecting pressure, so trying to increase the injecting pressure within the safe pressure threshold of coal seam, is an efficient solution to improve the methane recovery efficiency; (2) Initial coal permeability has positive impact on the performance of CO₂ replacing methane. Larger initial permeability accompanies with larger CO₂ injectivity; (3) Increase to coal elastic modulus results in lower coal permeability and CO₂ injectivity, showing that lower coal mechanical properties could be more suitable to binary gas diffusion.