From Pore to Core: Multi-Scale Evidence of Underground Hydrogen Storage Stability After Three Months of Hydrogen Exposure Under Reservoir Conditions

Underground hydrogen storage (UHS) is a cornerstone technology for net-zero energy systems, offering terawatt-hour capacity to buffer renewable intermittency. Although many experiments have been reported on hydrogen flow in porous rocks, robust evidence for long-duration reactions and impact on transport under combined high temperature and high pressure remains limited, leaving a critical uncertainty around reservoir stability during seasonal storage.

Here we provide firm, multi-scale pre/post experimental constraints on two major onshore UK candidate aquifers—the Triassic Sherwood Sandstone Group and the Cretaceous Lower Greensand Group—after ~3 months exposure to H₂ at simulated in-situ conditions deep underground, 50 °C and 150 bar. We integrate X-ray computed tomography (3D pore–grain architecture and bulk phase fractions), optical petrography (fabric/facies), SEM imaging (micro-textures and fines), and XRD (mineralogy) to resolve hydrogen impacts across scales. We also performed dynamic synchrotron images of hydrogen flows in the porous rocks to investigate the reaction impact on the transport. We performed systematically investigations on the pore networks, grain framework, or mineralogy, porosity and permeability. The results show  the pore network changes varied by <5%, consistent with measurement uncertainty. Only a single localised fines-migration feature (likely pyrite grain displacement) was detected, without associated dissolution/precipitation signatures. Quartz-dominated frameworks (>~65 wt%) appear inert under these conditions, while facies-scale heterogeneity governs pore connectivity and is expected to dominate injectivity and withdrawal behaviour. These results reduce a key uncertainty for UHS in silicate-rich sandstones, support prioritising connected macro-porous facies in site screening and well placement, and provide a transferable workflow for rapid hydrogen–rock interaction assessment and monitoring. Future work should extend to potentially more reactive lithologies, cyclic operation, longer exposure, and bio-active systems, in order to complete risk evaluation for large-scale seasonal storage.