Numerical simulation of heat CO₂ injection to increase CH₄

In this study, the coupling equation of binary gas diffusion-seepage-heat transfer field was established. COMSOL was used to simulate the change laws of displacement effect, CO₂ storage, CH₄ production and coal permeability during CO₂ displacement of CH₄ at different temperatures and pressures. The results show that CO₂ displacement will lead to CH₄ pressure rising higher than the original reservoir pressure in some area. CO₂ storage and CH₄ production increase with the increase of displacement pressure. When the displacement pressure increases from 2 MPa to 6 MPa, the displacement ratio increases from 2.85 to 4.38. However, when the displacement temperature increases from 20 ℃ to 100 ℃, the displacement ratio decreases from 4.38 to 4.34. In the process of displacement mining, displacement pressure is the main factor affecting the displacement effect. With the displacement, the influence range of CO₂ gradually increases. In the area affected by CO₂, the CO₂ injection has a great influence on the permeability of coal seam, the adsorption of CO₂ by coal matrix makes the permeability of coal seam decrease rapidly. In the area unaffected by CO₂, the coal permeability increases with the desorption of CH₄.