PORE-SCALE PERSPECTIVES ON MULTIPHASE FLOW DYNAMICS FOR UNDERGROUND HYDROGEN STORAGE IN BASALTIC RESERVOIRS

Abstract

The global transition to a low-carbon energy system has intensified the search for sustainable energy storage solutions, positioning hydrogen as a promising carrier for large-scale renewable integration. Underground hydrogen storage (UHS) in geological formations provides a viable approach to balance intermittent renewable supply with long-term demand. Unlike natural gas or \ce{CO2}, hydrogen exhibits distinct physicochemical behaviour in porous reservoirs because of its low viscosity, high diffusivity, and strong interfacial tension with brine. These properties lead to complex flow behaviours that remain poorly constrained, motivating pore-scale investigation to improve predictions of hydrogen storage and recovery.

This thesis integrates a comprehensive review of experimental and modelling studies with pore-scale simulations to elucidate the governing parameters of hydrogen–brine multiphase flow. Storage performance is controlled by the coupled effects of injection rate, wettability alteration, microbial activity, and pore-scale heterogeneities, which together dictate flow regimes, plume stability, and trapping efficiency. Despite research advances, uncertainties persist regarding the scalability of laboratory observations to field conditions, the evolution of hysteresis, and the limited characterization of mafic and ultramafic lithologies for UHS. To bridge these gaps, high-resolution micro-computed tomography (micro-CT) imaging and pore-network modelling are used to investigate displacement mechanisms. Results show that gas entrapment is primarily governed by snap-off and pore-body isolation, while transitions from strongly to weakly water-wet conditions promote brine reinvasion and enhance recovery efficiency. Successive drainage–imbibition simulations further reveal the progressive stabilization of hysteresis with repeated cycles, indicating the emergence of a hysteresis-equilibrium state.

Overall, this study establishes a quantitative link between pore-scale mechanisms and reservoir-scale behaviour. The integrated findings advance understanding of how wettability, interfacial phenomena, and pore structure govern hydrogen migration, trapping, and recovery. The resulting capillary pressure–saturation and relative permeability relationships provide transferable constitutive models for reservoir simulators, bridging laboratory observations with field-scale predictions of injectivity, storage capacity, and withdrawal performance.