Numerical Simulation of the Effect of Injected CO2 Temperature and Pressure on CO2-Enhanced Coalbed Methane

The injection of CO2 to displace CH4 in coal seams is an effective method to exploit coalbed methane (CBM), for which the CO2 injection temperature and pressure are important influential factors. We performed simulations, using COMSOL Multiphysics to determine the effect of CO2 injection temperature and pressure on CO2-enhanced coalbed methane (CO2-ECBM) recovery, according to adsorption/desorption, seepage, and diffusion of binary gas (CO2 and CH4) in the coal seam, and deriver a thermal–hydraulic–mechanical coupling equation of CO2-ECBM. The simulation results show that, as CO2 injection pressure in CO2-ECBM increases, the molar concentration and displacement time of CH4 in the coal seam significantly decrease. With increasing injection temperature, the binary gas adsorption capacity in the coal seam decreases, and CO2 reserves and CH4 production decrease. High temperatures are therefore not conducive for CH4 production.