Hydrogen storage caprock integrity: Challenges and mechanisms of clay-rich seals

Underground hydrogen storage (UHS) in porous media relies on clay-rich caprocks as primary seals ensuring containment. However, the coupled chemical and mechanical responses of these caprocks to hydrogen exposure remain insufficiently understood, limiting confidence in UHS safety. This review critically explores geochemical and geomechanical interactions between hydrogen and typical clay minerals, including kaolinite, montmorillonite, illite, and chlorite. Hydrogen alters pore structure, adsorption, wettability, and mechanical behavior through mineral dissolution, precipitation, and surface reactions. Geochemical models predict pH-driven processes such as illite dissolution and chlorite precipitation, while adsorption studies indicate weak physisorption compared with CO 2 and CH 4 . Molecular dynamics simulations reveal that surface chemistry governs wettability and capillary sealing. Cyclic hydrogen injection exacerbates stress variations, causing potential mechanical fatigue and leakage. Future work should integrate long-term, high-pressure/high-temperature experiments with multiscale reactive-mechanical modeling to improve predictions of caprock integrity and ensure the safe, sustainable deployment of UHS. • Caprock integrity in H 2 storage relies on geochemical and geomechanical factors. • H 2 exposure can alter porosity, with impacts depending on the mineral composition. • Clay minerals vary in H 2 adsorption, influenced by gas and subsurface conditions. • Water-wet conditions prevent H 2 leakage, but wettability changes need more study. • Cyclic H 2 injection affects caprocks, increasing risks of deformation and leakage.