Study on the micro-fracture-structure and permeability behavior of coal under the action of CO2 based on micro-CT

Abstract Permeability and porosity are critical parameters in CO 2 -ECBM and depend on the fine-scale fracture structure of coal. A self-developed high-pressure gas adsorption/desorption experimental system was used to conduct adsorption tests on coal at pressures ranging from 1 to 6 MPa. The CT scanning system was employed to scan coal samples before and after adsorption. This process established the three-dimensional fracture structure of the coal and simulated seepage behavior under different CO 2 pressures. After CO 2 adsorption, the fractures in the coal expanded significantly. The CO 2 pressure had a notable impact on internal fracture development. As CO 2 pressure increased, fracture structure parameters also increased, the fracture network became more complex and better connected, leading to an increase in the coal’s absolute permeability ( K ). The permeability was positively correlated with both the fractal dimension and porosity. The growth, expansion, intersection, and connectivity of microfractures caused by higher CO 2 pressure were the main reasons for the increase in porosity and permeability. These findings provide theoretical guidance for CO 2 geological sequestration and the development of coalbed methane resources.