Numerical simulation of fluid-solid-thermal coupling for CO2 injection enhanced mining in deep coal seams

Abstract

In order to study the effect of temperature effect on CO2 injection and gas extraction in deep coal seams, a fluid-solid-thermal coupling model for CO2-injection enhanced coal seam extraction was established based on the basic theory of coal deformation characteristics and gas seepage characteristics, which also considered non-isothermal adsorption, binary gas competitive adsorption, gas seepage and diffusion, heat transfer and heat convection. The influence of temperature effect on coal reservoir parameters and gas production evolution law is investigated. The results show that the shrinkage of coal matrix caused by coal bed temperature decrease promotes CH4 desorption, and the fluid-solid coupling model ignoring temperature effect will underestimate gas production. When the initial permeability is 3.95×10−17 m2 and the CO2 injection pressure is 8 MPa, for the deep coal body buried 1 400 m in the No. 3 coal seam in Hancheng Mining area, compared with the fluid-solid-thermal coupling model considering the temperature effect (319.5 K), the gas extraction time of 3 650 days is higher than that of the fluid-solid coupling model. The average gas pressure of coal seam decreased by 0.69%, the permeability of A point increased by 11.02%, the gas production rate increased by 13.51%, and the cumulative gas production increased by 13.76%.

Keywords

• gas drainage
• fluid-solid-thermal coupling
• co2 injection into coal seam
• coal-bed methane
• absolute permeability