Study on the competitive adsorption kinetics during water wetting in gas-bearing coal

Gas and dust disasters pose a significant threat to mine safety. Coal seam water injection is widely used to mitigate gas outbursts and dust hazards by displacing absorbed gas and improving coal wettability; however, the underlying dynamic process involves complex gas–liquid–solid three-phase interactions. To elucidate competitive adsorption between water and gas during wetting and to improve gas displacement efficiency, this study independently developed an experimental system for wetting gas-bearing coal. Through a combination of laboratory experiments and molecular simulations, we investigated the dynamic competitive adsorption behavior between gas and water molecules on the coal matrix surface. Experimental results indicate that during wetting of gas-bearing coal, increasing gas pressure promotes gas accumulation within pores, which hinders water migration and reduces the coal’s equilibrium water content by approximately 50%. Molecular simulations further reveal that as gas pressure increases, the coal's adsorption capacity for water gradually approaches saturation. After methane molecules desorb into the free phase, a dynamic barrier forms within the pores, decreasing the mean square displacement (MSD) and diffusion coefficients of both water and methane molecules by approximately 20%. This effect shifts the accumulation region of water molecules towards the outer surface of the coal molecular structure, thereby hindering effective wetting. These findings clarify the kinetic mechanism of water-flooding gas displacement in gas-bearing coal seams and provide a theoretical foundation for optimizing coal seam water injection strategies to enhance mine safety.