Geochemical reactions in reservoir rock and capillary sealing capacity of caprock during hydrogen admixing in the underground gas storage complex Rehden

A comprehensive laboratory study evaluated the feasibility of hydrogen storage in the Rehdenunderground gas storage (UGS) complex, emphasising geochemical interactions and capillary sealingcapacity. Core samples from reservoir rocks and caprock were tested under hydrogen and methaneatmospheres at reservoir conditions. Geochemical analyses indicated minor mineralogical and fluidcompositional changes due to hydrogen, suggesting minimal impact on reservoir integrity. Capillary entrypressure experiments demonstrated robust sealing efficiency of caprock, comparable to methane, with slightvariations in interfacial tension and wettability. Geochemical modelling predicted negligible changes inporosity and permeability, affirming the geological suitability of Rehden UGS for hydrogen storage,providing vital insights into the risk assessment for future hydrogen storage operations.