Abstract
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.
Highlights
Coalbed methane (CBM) in coal seams is usually stored as free gas in cracks and pores and adsorbed gas on organic surfaces [1]
CO2 -enhanced coalbed methane (CO2 -ECBM) technology involves the injection of CO2 into a coal seam rich in CBM, to sequester CH4, promotes clean green energy, and is widely used in the production of deep ultra-low permeability coal seams [10,11,12,13,14]
To study the effects on gas recovery and coal seam permeability, we used COMSOL Multiphysics to simulate the process of injecting CO2 with different pressures and temperatures to displace coalbed methane
Summary
Coalbed methane (CBM) in coal seams is usually stored as free gas in cracks and pores and adsorbed gas on organic surfaces [1]. Vishal used numerical simulations to study the production effect of coal with different sorption times under CO2 action Their results indicate that the CO2 injection capacity of coal with high sorption time is higher than that of coal with low sorption time [23]. Fang established a fully coupled equation of gas diffusion, adsorption, seepage, and heat transfer and simulated the displacement process and effective influence radius of injected CO2 under different pressure and temperature conditions [26]. To study the effects on gas recovery and coal seam permeability, we used COMSOL Multiphysics to simulate the process of injecting CO2 with different pressures and temperatures to displace coalbed methane
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