Physical and geochemical alterations in reservoir and caprocks induced by long-term H2-brine-rock interactions

Abstract

Deep saline aquifers offer significant potential for large-scale hydrogen (H₂) storage due to their substantial capacity and high recovery purity. However, the long-term impacts of H₂ injection on reservoir rock and caprock integrity remain poorly understood. This study investigates the physicochemical responses of five representative reservoir and caprocks (sandstone, basalt, limestone, shale, mudstone) to H₂ exposure under simulated aquifer conditions (15 MPa, 60 °C) over 75 days, complemented by century-scale (100-year) geochemical modeling using PHREEQC 3.7. Short-term experimental results revealed negligible alterations in porosity, density, pore structure, mechanical properties, or micro-scale morphology. In contrast, long-term simulations predicted substantial dissolution of carbonate minerals (calcite, dolomite, siderite) and significant H₂ loss in shale (53.20 %), limestone (43.23 %), and mudstone (37.36 %) systems, attributed to enhanced H₂ dissociation and acid-driven reactions. Silicate minerals exhibited minimal reactivity over 100 years. Trace methane generation was observed in carbonate-rich systems. These findings indicate that while silicate-dominated formations are suitable for long-term storage, carbonate-rich caprocks pose leakage risks due to mineral dissolution and associated H₂ consumption.