Study on the mechanism of water injection pressure and fractures on wetting and diffusion of hard rock during water injection

To reveal the influence mechanism of water injection pressure and fracture characteristics on hard rock moisture diffusion, this study selects sandstone as the research object and combines low-temperature high-pressure nuclear magnetic resonance tests with COMSOL Multiphysics numerical simulations. Current research has widely applied nuclear magnetic resonance for fluid distribution analysis and COMSOL for seepage simulation, but their coupling to clarify the combined effects of pressure and fractures on hard rock wetting remains insufficient, especially for high-density, low-porosity hard rock with poor permeability. This study systematically investigates water migration under varied pressures and fracture lengths. Experimental results show moisture increase is dominated by adsorbed water, and nuclear magnetic resonance T 2 spectral peak area expands significantly with pressure and time, proving high pressure effectively opens closed pores and enhances seepage channel connectivity. Simulation results demonstrate that the wetting radius exhibits an exponential relationship with water injection pressure: it increases markedly when the pressure is below 11 MPa, stabilizes once exceeding this threshold, and reaches a maximum of approximately 2.25 m. Additionally, the wetting radius grows linearly with fracture length, indicating that longer fractures can effectively broaden the water diffusion range. These findings elucidate the dominant role of pressure and fractures, providing theoretical guidance and technical support for optimizing water injection parameters, improving wetting efficiency, and enhancing mining dust suppression.