Influence of Coal Micropore Network on Gas–Liquid Two-Phase Transport

To analyze the influence of coal micropores on gas–water two-phase transport, 660 coal microsurface images were scanned using focused ion beam-scanning electron microscopy (FIB-SEM), followed by three-dimensional (3D) modeling of coal micropores through the gray-value binarization segmentation technique. Microstructural characteristics, including micropore connectivity, were computed and statistically analyzed. Findings indicate that the coal micropore structure displays a networked distribution with the 100–500 nm pore size range serving as the primary region for fluid retention and transport. Subsequently, the low-field nuclear magnetic resonance (LF-NMR) T2 spectra of coal under varying water injection times were examined using a water injection and gas drive-triaxial in situ LF-NMR experimental platform, assessing the role of time on gas and water transport in the coal multiscale pore structure and evaluating how micropore connectivity affects the gas–liquid two-phase transport process. Results reveal that microporous structures with enhanced connectivity are prone to gas-phase stagnation areas due to water blockage and dominant channels; this stagnant gas incrementally dissolves into the water, causing the gas–liquid interface to progress toward the stagnation region over a defined time scale. A porous coal matrix model was constructed via molecular dynamics, validating this gas retention process and illustrating transport differences between the gas and liquid phases in the connected pores. These findings offer a microscale foundation for understanding gas- and water-phase transportation in coal multiscale pores, potentially aiding in optimizing water injection and gas displacement strategies in coal seams.