Effect of CO2 injection on the gas desorption and diffusion kinetics: An experimental study

During CO2 displacement, the diffusion characteristics of gas in the coal matrix are among the key factors that affect the gas extraction rate, and discussed the influence mechanism of CO2 injection on the diffusion kinetics of coal seam gas. In this study, we used a self-developed CO2–CH4 displacement experimental platform to study the diffusion characteristics of CH4 under different CO2 injection pressures and temperatures. As the CO2 injection pressure was increased from 0.6 MPa to 1.0 MPa, the CH4 production increased by 9.44 %, the CH4 maximum diffusivity increased by 0.05, the effective diffusion coefficient extreme point increased by 111.45 %. As the gas injection temperature was increased from 40 °C to 60 °C, the CH4 production increased by 4.02 %, the CH4 maximum diffusivity increased by 0.03, the maximum of the effective diffusion coefficient increased by 103.31 %. To better explain the gas diffusion characteristics during CO2 displacement, the influence mechanism of increasing CO2 injection pressure and temperature on the CH4 diffusion kinetics was discussed, and the driving force (fd) and resistance (fr) during the displacement process were studied. The dynamic CO2 injection models were considered to be more effective in ensuring efficient CH4 recovery.