Numerical Simulation of CO2-ECBM Based on Multi-Physical Field Coupling Model

Abstract

In this paper, heat injection and CO2 injection are combined, and the influence of coal seam parameters on CO2-ECBM is analyzed to improve the production of CH4 and CO2 reserves and the effective control of both greenhouse gases. A multi-physical field coupling model of CO2-ECBM was established based on Darcy’s law, Fick’s law of diffusion, the extended Langmuir model for adsorption, and the equation of state. Numerical simulation of CO2-ECBM under different coal seam parameters was carried out by COMSOL Multiphysics. The results show that increasing the injection pressure of the CO2 injection well and the initial pressure of the coal seam can effectively increase the gas pressure and concentration gradient, which has a positive effect on improving the extraction concentration of CH4 and the sequestration concentration of CO2 in the coal seam. The increase of the initial temperature of the coal seam will promote the desorption and diffusion of the binary elemental gas, resulting in a decrease in the concentration of coalbed methane and a decrease in the displacement effect. In the process of displacement, the greater the initial permeability, the greater the fracture opening of the coal seam, which is more conducive to the seepage transport of the gas. The closer to the position of the injection well, the better the displacement effect and the lower the permeability rate ratio.