Coal-Body Structural Evolution, Multiscale Pore-System Reorganization, and Methane Storage-Transport Characteristics Across a Tectonic Deformation Gradient

Tectonic deformation can reorganize adsorption-related pores, matrix pore space, and pore-throat-fracture networks, but how these functional domains jointly govern fluid mobility and permeability stability under stress remains unclear where deformation intensity and coal rank covary. We investigated the B4 coal seam along the Qujiang-Shangzhuang-Yuancun transect in the western Pingxiang-Leping Depression Belt using a combination of field-emission scanning electron microscopy (FE-SEM), low-pressure CO2 adsorption, low-temperature N2 adsorption, mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), methane adsorption, and N2 gas-permeability stress-sensitivity tests. Along the transect, coal-body structure changed from primary-structure and cataclastic coal to granulated and mylonitic coal within a regional context of increasing coal rank, decreasing volatile-matter content, and fewer open fractures. Despite comparable Langmuir volumes (16.29–19.96 cm3 g−1), transport-related properties differed markedly. Qujiang samples contained 23.48–30.04% of their method-accessible pore volume in the >100 nm interval and had movable-fluid saturations of 44.7–53.1%. Shangzhuang samples exhibited irreversible N2 gas-permeability damage of 98.63–99.99%, whereas the Yuancun sample contained abundant method-accessible pore volume across all operational size intervals but had a movable-fluid saturation of only 19.21%. Thus, accessible pore volume does not necessarily correspond to connected, stress-stable transport pathways. Favorable coalbed methane intervals require sufficient adsorption-storage space combined with connected, mechanically stable pore-throat-fracture networks.