Microscopic pore controls on seepage behavior in varied coal structures based on dual-scale digital core analysis.

Tectonic deformation induces multiscale modifications in the pore-fracture morphology of coal, fundamentally altering its seepage behavior. These structural changes are critical to understanding fluid migration and gas outburst risks in coalbed methane (CBM) reservoirs. This study integrates micron and submicron-scale X-ray computed tomography (CT) with pore network modeling (PNM) to investigate how geometric and topological parameters influence flow in primary (PC) and tectonic coals (TC). PC exhibits intact structures with bedding-parallel fractures that are laterally continuous and moderately connected at the micron scale. Submicron pores show uniform morphology and multidirectional connectivity. TC contains more non-directional macro-fractures, resulting in stronger connectivity but pronounced spatial heterogeneity. Submicron pores in TC display higher tortuosity and morphological complexity. PNM-based seepage simulations indicate that, at the micron scale, PC maintains smooth flow paths with uniform velocity and stable pressure decay, whereas TC shows direction-dependent flow with coexisting high- and low-permeability zones and significant vertical pressure gradients. At the submicron scale, PC exhibits variable multidirectional seepage, while TC presents more stable but directionally preferential migration. Correlation analysis reveals a scale-dependent shift in permeability control-from coupled geometric and topological effects at the micron scale to connectivity and throat-size sensitivity at the submicron scale.