Numerical study of CO2-enhanced coalbed methane recovery.

Although CO 2 -enhanced coalbed methane (CO 2 -ECBM) recovery has been comprehensively investigated, fewer scholars have taken the effect of temperature into account, which brought a large deviation for the study of the influence of CO 2 -ECBM. In this work, a hydraulic-mechanical-thermal coupled model of CO 2 -ECBM is established, it combines binary gases (CO 2 and CH 4 ) infiltration and diffusion, where non-isothermal adsorption is also considered. The effect of injection pressure and reservoir initial temperature on CO 2 -ECBM was simulated by the finite element simulation software COMSOL Multiphysics, results show that: the injection of CO 2 into coalbed has a good effect on enhancing the production of CH 4 , and both the CO 2 storage rate and CH 4 production rate increase with the increase of injection pressure. The effect of initial reservoir temperature on CO 2 -ECBM is obvious. Since the amount of adsorbed gas in coal decreases with the increase of temperature, the CO 2 storage rate and CH 4 production rate decrease with the increase of initial reservoir temperature. In the gas extraction process without CO 2 injection, the variation of permeability is competition result of two types of factors: the coal matrix shrinkage caused by temperature reduction and gas desorption increase, the other is the coal matrix expansion caused by gas pressure decrease, so the permeability follows the rule of first decreasing and then increasing with the extraction time. The injection of CO 2 has a great influence on the permeability of coalbed, adsorption of CO 2 by the coal matrix causes the permeability to drop rapidly. [ABSTRACT FROM AUTHOR]