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

This is the authors' abstract. We don't add key points for this paper.

As the world moves away from fossil fuels in a ‘green energy transition’, low-carbon alternatives such as renewable energy technology is becoming progressively abundant. Renewable energy production is extremely weather-dependent, fluctuating on a daily and seasonal scale, leading to mismatches between production and demand that can only be mitigated through energy storage. 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. Salt-caverns can provide small-medium scale hydrogen storage, but for larger seasonal-scale storage, porous rock storage is necessary. 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 reactivity hydrogen ions. This study evaluates the current disparity in the literature regarding the impacts and extents of hydrogen-induced abiotic reactions, with a significant agreement being the lack of reaction between hydrogen and rock-forming (alumina) silicate minerals, and a strong likelihood that under reservoir conditions (heightened temperature and pressure) hydrogen can reduce pyrite to pyrrhotite. There is also compelling evidence suggesting exposure to hydrogen can lead to the dissolution of sulphates (anhydrite) and carbonates (calcite). Ultimately, this review contains no show-stopping evidence preventing future developments of underground hydrogen storage (UHS) in saline aquifers. We have identified gaps in the knowledge that are required to establish a clear understanding of extents and rates of all potential mineral reactions to ensure accuracy of reservoir models and field-scale geological analysis.