Pore-scale Evaluation of Hydrogen Storage and Recovery in Basaltic Formations

Underground hydrogen storage (UHS) in basaltic rocks offers a scalable solution for large-scale sustainable energy needs, yet its efficiency is limited by poorly constrained pore-scale hysteresis during cyclic hydrogenbrine flow. While basaltic rocks have been extensively studied for carbon sequestration and critical mineral extraction, the pore-scale physics governing cyclic hydrogen-brine interactions, particularly the roles of snap-off, wettability, and hysteresis, remain inadequately understood. This knowledge gap hinders the development of predictive models and optimization strategies for UHS performance. This study presents a pore-scale investigations of cyclic hydrogen-brine flow in basaltic formations, combining micro-computed tomography imaging with pore network modelling. A systematic workflow is employed to evaluate the effects of repeated drainage-imbibition cycles on multiphase flow properties under varying wetting regimes, with emphasis on hysteresis evolution and its influence on recoverable hydrogen. Model validation is achieved through a novel benchmarking approach that incorporates synthetic fractures and morphological scaling, enabling calibration against experimental capillary pressure and relative permeability. Results show that hydrogen trapping is primarily governed by snap-off and pore-body isolation, particularly within large, angular pores exhibiting high aspect ratios and limited connectivity. Strong hysteresis is observed between drainage and imbibition, with hydrogen saturations averaging 85%, predominantly in larger pore spaces, compared to a residual saturation of 61% following imbibition. Repeated cycling leads to a gradual increase in residual saturation, which eventually stabilizes, indicating the onset of a hysteresis equilibrium state. Wettability emerges as a critical second-order control on displacement dynamics. Shifting from strongly to weakly water-wet conditions reduces capillary entry pressures, enhances brine re-invasion, and increases hydrogen recovery efficiency by ∼6%. These findings offer mechanistic insights into capillary trapping and wettability effects, providing a framework for optimizing UHS reactive and abundant, yet underutilized, basalt formations, and supporting ongoing global decarbonization efforts through reliable subsurface hydrogen storage.