Evolution law of coal seam permeability in CO₂-ECBM process

In order to study the spatio-temporal evolution law of coal seam permeability in the process of CO₂-ECBM, a CO₂-ECBM fluid-solid-thermal multi-field coupling numerical model is established by using COMSOL Multiphysics numerical simulation method based on the geological conditions of Liliu Mining Area as the engineering background. The CO₂-ECBM process is numerically simulated by five-point well layout method, and the spatio-temporal evolution of coal permeability with CO₂ injection is discussed. The results show that gas pressure, CO₂ injection and shrinkage/expansion deformation of coal matrix are the key factors affecting permeability evolution. After the adsorption of CO₂, the expansion deformation of coal matrix plays a leading role, occupying the pore space, resulting in the decrease of permeability, the mean permeability in the range affected by CO₂ decreased by 40%. Along the CO₂ injection well to the extraction well, the permeability is less and less affected by CO₂, it shows a monotonic upward trend. The mean permeability increased by 14% outside the influence range of CO₂.