Geochemical responses of mineral powder materials and natural rock cores to H2-water exposure in underground hydrogen storage

Geochemical interactions among H 2 , water, and subsurface minerals may affect the integrity of underground hydrogen storage (UHS). Five mineral-enriched powders and one cement material were exposed to H 2 gas, He-water, and H 2 -water for 30 days at 120 °C and 10 MPa. Sandstone, mudstone, and carbonate rock cores were examined before and after H 2 -water exposure. Water-mineral interactions dominated the observed mineralogical changes. Relative dolomite, kaolinite, and illite abundances were 83.10%, 38.06%, and 23.02% in He-water and 82.55%, 37.46%, and 22.47% in H 2 -water, respectively, indicating limited additional H 2 effects. The cement showed more pronounced redistribution of Ca-bearing phases, whereas feldspar-rich and muscovite-rich materials showed comparatively weak responses. Natural rocks retained their fabrics, with localized changes near microfractures. Mineral reactivity, water availability, and rock fabric jointly controlled short-term H 2 -water-rock interactions under the experimental conditions. This study provides a foundation for understanding the mineralogical and microstructural responses of reservoir rocks in UHS.