Microscopic Gas Seepage Simulation Based on Multidimensional Characteristics of Pore-Fracture Networks and Digital Cores

With the advancement of the strategic goals of “carbon neutrality and carbon peak”, Carbon Dioxide-Enhanced Coal Bed Methane Recovery (CO₂-ECBM) technology has emerged as a research hotspot. However, the process of CO₂ injection into coal seams can alter the pore and fracture distribution field, affecting the gas seepage field. This study investigates pore distribution patterns, topological structures, gas seepage mechanisms, and spatial characteristics of Pingdingshan coal samples using a coupling approach of 3D reconstruction technology and Fluent numerical simulation. Results derived from the aforementioned investigations are as follows: (1) In the coal sample pore structure, 92.61% of the pore count exhibits a pore size distribution within 20–100 μm, yet these contribute only 23.03% to the total pore volume. (2) The spatial proportion of fractures inclined in the direction perpendicular to the X axis reaches 60.27%. Therefore, the permeability of the coal sample in the Z axis direction is 4.5 times that in the X axis direction, forming a preferential gas seepage channel in the Z axis direction. (3) When gas seepage occurs in complex pore structures, both seepage pressure and velocity exhibit nonlinear decreases with increasing seepage distance. While the choice of preferential pathways in gas seepage remains unaltered under both constant and nonconstant pressure conditions, the latter influences the selection of nonpreferential pathways. The findings of this study offer theoretical insights for CO₂-ECBM by elucidating pore-fracture network controls on gas transport under variable pressure regimes.