Pore-scale numerical investigation of hydrogen-brine transport in a saline aquifer sandstone: Influence of contact angles and pressure differences

To fully investigate the underground hydrogen storage technology, this paper particularly focuses on the two-phase pore-scale transport characteristics of hydrogen-brine in saline aquifer. By reconstructing the three-dimensional digital core of real sandstone and developing a pseudo-potential lattice Boltzmann model (LBM) that accounts for the gas slippage effect, this study systematically investigates the dynamic influence of wettability (contact angles of 30°, 50°, and 70°) and displacement pressure difference (15, 25, and 35 MPa) on the two-phase distribution morphology and relative permeability curves of the hydrogen-brine system. Results demonstrate that: (1) During the process of hydrogen displacing brine, reducing the hydrophilicity of aquifer weakens snap-off effect, providing more pore space for hydrogen accumulation and improving storage efficiency; however, the displacement pressure difference presents a relatively limited effect on the breakthrough velocity of phases; these should be attributed to the high interfacial tension and low viscosity of hydrogen-brine system, thus snap-off effect predominantly governs phase migration. (2) Within the investigated sandstone structure, enhancing hydrophilicity decreases the relative permeability of the brine phase but increases that of the hydrogen phase above a certain gas saturation threshold. (3) Gas slippage effect leads to three-stage tendency in gas-phase relative permeability: an initial slow increase, followed by accelerated growth, then eventual stabilization; whereas water-phase relative permeability exhibits a rapid rise followed by a stable trend. (4) Notably, in the tested cases, these physical processes suggest that controlling the contact angle of aquifer to approximately 50° is beneficial for enhancing the performance and stability of hydrogen storage.