Analysis of Mutual Interference Mechanism Binary Gas Diffusion Based on Time-Dependent Effect in the CO₂-Enhanced Coalbed Methane Process

CO2-enhanced coalbed methane (CO2-ECBM) is a key method for increasing CH4 production and CO2 storage. Researching the diffusion patterns of gases in coal is an important direction for CO2-ECBM. In previous studies on the diffusion patterns of gases in coal, the diffusion coefficient was usually considered a constant. However, it has been proven that the diffusion coefficient has a strong dependence on concentration and time. Moreover, existing time-dependent diffusion models have primarily been used to study the diffusion process of CH4 in pores, with little attention given to the role of time-dependent effects in binary gas systems. Therefore, this paper establishes a concentration-dependent time-dependent diffusion model. Experimental data on the desorption amount and desorption rate of CH4 and CO2 were obtained to fit a time-dependent diffusion coefficient. The mutual disturbance effects in the binary gas system during CO2 injection were also considered. Specific parameters were introduced to adjust the time-dependent diffusion coefficient based on the pressure difference ratio. Through comparative analysis of gas concentration changes during displacement using both constant and time-dependent diffusion models, the impact of time-dependent effects on gas diffusion behavior during injection, as well as CH4 recovery and CO2 storage, was studied.