Hydrogen Storage Potential of Unlined Granite Rock Caverns: Experimental and Numerical Investigations on Geochemical Interactions

Underground Hydrogen Storage (UHS) offers a promising solution for large-scale energy storage, yet suitable geological formations are often scarce. Unlined rock caverns (URCs), constructed in crystalline rocks like granite, present a novel alternative, particularly in regions where salt caverns or porous media are unsuitable. Despite their potential, URCs remain largely unexplored for hydrogen storage. This study addresses this gap by providing one of the first comprehensive investigations into the geochemical interactions between hydrogen and granite host rock, using a combined experimental and numerical approach. Granite powder samples were exposed to hydrogen and inert gas (N₂) in brine at room temperature and 5 MPa pressure for 14 weeks. Results showed minimal reactivity of silicate minerals with hydrogen, indicated by negligible differences in elemental concentrations between H₂ and N₂ atmospheres. A validated geochemical model demonstrated that existing thermodynamic databases can accurately predict silicate‑hydrogen interactions. Additionally, a kinetic batch model was developed to simulate long-term hydrogen storage under commercial URC conditions at Haje. The model predicts a modest 0.65 % increase in mineral volume over 100 years due to mineral precipitation, which decreases net porosity and potentially enhances hydrogen containment by limiting leakage pathways. These findings support the feasibility of granite URCs for UHS, providing a stable, long-term storage option in regions lacking traditional geological formations. By filling a critical knowledge gap, this study advances scalable hydrogen storage solutions, contributing to the development of resilient, renewable energy infrastructure.