Study on the effect of morphology of anthracite coal containing through-fracture on CO2 enhanced coalbed methane recovery

When CO2 is injected into the coal seam, different forms of fractures within the coal have different effective diffusion areas and distribution characteristics for the gas, affecting methane's adsorption-desorption-diffusion and seepage behavior. In this study, based on the control experiments of the intact coal sample, CO2 injection experiments were carried out on three groups of coals containing through-fracture to investigate the influence of fracture morphology on CO2-enhanced coalbed methane recovery behaviors and to discuss and analyze the changes in the volume of the coal samples, the composition of the tailing gas, and the changes in the permeability during the gas injection process. The results show that: the existence of fractures has an inhibitory effect on the volume expansion after gas adsorption of the coal, and the larger the surface area of fractures, the more obvious inhibitory effect, and at the same time, the faster the strain rate; the breakthrough time of CO2 in the fractured coal samples is much shorter than that in the intact samples; the increase in the surface area of the fractures and uniformity of distribution can enhance the concentration of CH4 in the tail gas, and in the pre-injection stage, uniformity of the distribution of the fractures is more important than the surface area of the fractures in increasing the output CH4 concentration; the magnitude of permeability change and the change rate of the coal samples during CO2 injection increased with the increase in the fracture surface area of the coal samples.