Reactivity of Natural Rock Salts of Different Genesis under Underground Hydrogen Storage Conditions

Hydrogen energy storage in geological formations is increasingly regarded as a key component of a future low-carbon energy system. Among potential reservoir rocks, salt formations are particularly attractive due to their extremely low permeability, low chemical reactivity, and self-healing behaviour, all of which favour long-term storage integrity. However, natural salt deposits differ in genesis, texture, and impurity content, which may influence their geochemical response to underground hydrogen storage (UHS) conditions.

This study compares the chemical–mineralogical reactivity of rock salt formations of different origins when exposed to hydrogen. Three salt types were studied: the Oligocene Barbastro Formation (Ebro Basin, Spain), the Triassic Atauri Formation (Basque-Cantabrian Basin, Spain), and a commercially available Himalaya salt. Owing to their distinct depositional environments and post-depositional histories, these materials exhibit subtle differences in texture and mineralogical composition. Samples were exposed to hydrogen gas under representative UHS conditions in a high-pressure vessel (p = 10 MPa, T = 60 °C) for 30 days under batch conditions. Pre- and post-exposure characterisation was performed using X-ray diffraction and scanning electron microscopy to assess potential mineralogical and textural changes.

The results indicate that all three salt types undergo only minor alterations under the investigated conditions and timescale, confirming the overall chemical stability of halite in a hydrogen storage context. The only notable differences in reactivity are associated with the presence of gypsum as an accessory phase, which locally influences mineralogical responses. These findings support the suitability of a wide range of natural salt formations for underground hydrogen storage, while highlighting the importance of impurity phases in site-specific assessments.

The research was conducted within the Project UES365, the Project H2Salts and the Format-GEO collaboration network (LINCGLOBAL 25008).

References:

Kovács, T., Mediato, J., Ordóñez, B., Garcia-Mancha, N., Santolaria, P., Calvín, P., Sanchez Guzman, J., Gracia, J., Roces, S., Mata Campos, P., and Berrezueta, E.: Preliminary laboratory studies on hydrogen storage in a salt cavern of the Eocene Barbastro Formation, Southern Pyrenees, Spain, Adv. Geosci., 67, 15–24, https://doi.org/10.5194/adgeo-67-15-2025, 2025.