Impact of Permeability on Hydrogen-Water Relative Permeability and Cyclic Underground Hydrogen Storage Performance

Underground hydrogen storage (UHS) in aquifers demands reliable relative permeability data set concerning hydrogen–water flow dynamics. This study provides a systematic assessment across low, medium, and high permeabilities (ranging from 16.5 to 1220 mD) using cyclic drainage–imbibition core-scale experiments under gravity-stable conditions. Quantitative results show the strong influence of permeability on both storage and recovery: in the first cycle, the stored hydrogen saturations increase from 27.0 to 64.3 and 76.0%, with corresponding recoveries of 41.1, 79.2, and 85.7% in low-, medium-, and high-permeability cores, respectively. Injection-production cycles raise both stored and remaining hydrogen saturations in all cores, however the hysteresis systematically decreases with increasing permeability. End-point relative permeabilities reflect the same trend: hydrogen end point is found generally low, increasing from approximately 0.018 to 0.051 and 0.095 in high permeability cores. In contrast, water end points increase comparatively less with permeability, ranging from approximately 0.87 to 0.91 and 0.97. A key finding is that hysteresis decreases as the permeability of the rock increases. Mechanistically, low-permeability cores exhibit capillary-dominated displacement at the core-scale and poor performance, where hydrogen gas breaks up into isolated clusters with limited reconnection during cycling. In contrast, high-permeability cores establish broader and more continuous gas phase across the core volume, improving storage and withdrawal efficiency, even though a measurable fraction of hydrogen remains trapped as residual gas. These new core-scale data set quantify how permeability affects relative permeability, hydrogen storage withdrawal, and hysteresis evolution during cyclic drainage-imbibition and thus aid in reservoir-scale screening and predictive simulation of UHS performance.