Wetting-Diffusion Mechanisms in Dual-Pore Channels of High-Temperature Steam-Modified Coal: Multiscale Experiments and Molecular Dynamics Study

Steam injection is widely used for enhanced coalbed methane recovery; the coupled effects of pore structure, wettability, and CH 4 displacement under high-temperature steam remain poorly understood. Clarifying this mechanism is critical for optimizing injection parameters and utilizing industrial waste heat. Anthracite A and bituminous coal B treated at 100–500 °C were analyzed via contact angle, LF-NMR, in situ FTIR, electrostatic potential, and molecular dynamics. Results show that 100 °C is the optimal wetting threshold, with contact angles increasing marginally to 52.5 and 102°, and free water shifting from P 2 to P 1 . Above 300 °C, hydroxyl and C–O bonds decreased 32–46%, and A exhibited more hydrogen bond weakening despite lower oxygen content with ESP of −0.1823 au. Simulations revealed 43–61% hydrogen bond reduction, bond elongation to 2.02 Å, and 30° deviation, converting clusters to monomers. At 500 °C, diffusion coefficients reached 10.3 Å 2 /ps in A versus 5.97 Å 2 /ps in B. At 300 °C, interaction energies decreased to 6871 and 1793 kcal mol –1 in A, enabling methane desorption and three-stage water penetration, while B maintained stable films. High-temperature hydrogen bond rupture enhances diffusion, but optimal wettability occurs near 100 °C, revealing nonsynergistic evolution between diffusivity and wettability. These findings clarify the wetting-diffusion coupling mechanism in dual-pore channels of different rank coals under thermal steam, and provide theoretical support and engineering guidance for enhanced coalbed methane recovery and resource utilization of industrial waste heat steam.