A General Hydrogen Mass-Transport Model for Porous Media with Limited Material-Information Demand

Underground hydrogen storage in porous formations requires numerical models able to represent multiphase flow, gas dissolution, diffusion, capillary effects, and gas mixture behaviour under conditions that may involve temperature changes, salinity and deformation. This work presents a general abiotic compositional formulation for hydrogen mass transport in water-wet porous media and its implementation in a new numerical model, X2H+. The formulation describes advective, diffusive and dispersive transport in gas and liquid phases and incorporates non-ideal gas behaviour, hydrogen dissolution in brine, water-vapour equilibrium, salinity-dependent liquid properties, porosity-dependent intrinsic permeability, and porosity-dependent capillary behaviour. The reservoir-scale transport response of X2H+ was numerically qualified against a multi-code benchmark involving hydrogen injection into an initially water-saturated axisymmetric aquifer. The model reproduces the gas-saturation evolution reported for the benchmark, with deviations comparable to those observed among the reference numerical models. The formulation also limits additional material-information demand by evaluating many extended transport terms through transferable equations of state, thermodynamic correlations, and physicochemical relationships rather than through new porous-medium-specific parameters. X2H+ provides a flexible basis for advanced underground hydrogen storage simulations while retaining a manageable material-characterisation requirement.