Influence of uniaxial strain loading on the adsorption-diffusion properties of binary components of CH4/CO2 in micropores of bituminous coal by macromolecular simulation

Heterogeneous and anisotropic coal tends to deform under strong mining disturbances, affecting the microscopic adsorption and diffusion of binary CH4-CO2 mixtures in micropores. Therefore, the grand canonical Monte Carlo and molecular dynamics methods were used to study the influence of the uniaxial strain loading on the adsorption-diffusion properties of binary components of CH4/CO2 in coal micropores. The results show that compression strain has significant effects on adsorption selectivity and thermodynamic factor compared to tension strain, and CH4 displacement efficiency is greater when the strain is less than −0.12. Both compression and tension strains have dual effects on promotion and inhibition of volumetric swelling of the gas-containing coal matrix, micropore development and gas diffusion. Furthermore, the diffusivity of CH4 is significantly larger than that of CO2, and Einstein diffusion is dominated by low-velocity motion. Results provide an important basis for the optimal coalbed methane recovery design in deformed coal reservoirs. [Display omitted] •Competitive adsorption and bulk CH4 mole fraction increase CO2 adsorption difficulty.•Strain has dual effects on volumetric swelling, micropore development, and gas diffusion.•CH4 diffusivity is greater than that of CO2 and lower strain level improves gas diffusion.•Einstein diffusion is dominated by low-velocity motion in coal micropores.