Effects of an Acidic Nanofluid–Surfactant Compound Solution on Coal Pore Structure and Gas Adsorption and Desorption

The low wettability and poor permeability of deep coal seams limit the efficacy of conventional water injection for gas recovery. Here, we report an acidic ZnO/SDBS nanofluid system that simultaneously modifies coal surface chemistry and pore structure through an integrated interfacial engineering approach. Under optimized conditions (1.0 wt % ZnO, 0.15 wt % SDBS, pH = 3), the nanofluid reduces the coal contact angle to 27.9°, enhances wettability by 67.4%, and increases total pore volume by 41.3% while reducing specific surface area. These changes promote competitive water adsorption, suppress methane adsorption, and improve gas transport pathways. The results demonstrate a scalable, chemical-based process intensification strategy for enhancing coal seam methane extraction, with potential applications in other subsurface resource recovery operations involving low-permeability porous media.