Hydrogen-induced mineral alteration: a review in the context of underground hydrogen storage (UHS) in saline aquifers

Hydrogen is considered a viable energy vector, it can be produced through the electrolysis of water and stored as a gaseous phase in the subsurface. Hydrogen storage in saline aquifers is not yet commercially operational, to increase the technological readiness, the complex interactions between rock, pore fluid, and hydrogen under reservoir conditions (increased pressure and temperature) need thorough understanding. It is acknowledged that abiotic geochemical reactions are a potential barrier for UHS as hydrogen is an electron donor and can form highly reactive hydrogen ions. Using a comparative approach, this study reviews the current disparity in the literature regarding the impacts and extents of hydrogen-induced abiotic reactions, to identify knowledge gaps requiring further investigation. Data from both experimental and modelled methods are summarised in relation to individual minerals, common in the subsurface, and their implications to efficiency and security of underground hydrogen storage. This review demonstrates a significant agreement concerning the lack of reaction between hydrogen and rock-forming silicate minerals, and a strong likelihood that under reservoir conditions (heightened temperature and pressure) hydrogen can reduce pyrite to pyrrhotite. It also reveals compelling evidence suggesting exposure to hydrogen can lead to the dissolution of sulphates (anhydrite) and carbonates (calcite). We conclude development of future hydrogen storage projects in saline aquifers should therefore focus on silicate-rich formations. And further work is needed to establish a clear understanding of extents and rates of potential mineral reactions to ensure storage security and efficiency in future projects.