Computerized tomography analysis of potential geochemical reactions of carbonate rocks during underground hydrogen storage

The research on Hydrogen (H-2) gas has attracted considerable attention as a clean energy source to achieve net-zero carbon emissions. Underground Hydrogen Storage (UHS) in carbonate reservoirs is a suitable solution for safe storage and efficient recovery of hydrogen during the cycling process. However, the potential geochemical reactions between hydrogen and carbonate minerals can influence the storage potential and rock characteristics. Despite the current devotion to evaluating H-2-rock interactions, there is a lack of knowledge on the reactivity of carbonate rocks to hydrogen and the potential implications on pore properties. In this work, carbonate rocks were subjected to hydrogen treatment at 75 degrees C and 1400 psi for 150 days, and a comprehensive Computerized Tomography (mu-CT) scan analysis was performed. The results confirm the occurrence of geochemical reactions of dolomite and calcite with H-2, however, the extent of mineral alteration is minimal, and the dissolution/precipitation rates are nearly balanced. Subsequently, insignificant changes in porosity (not exceeding 2 %) and grain expansion are observed. However, we observed unexpected development of fractures within 75-150 days of treatment in the calcite sample, which we believe is related to the de-pressurizing of the samples after 75 days of treatment, and not because of hydrogen reactions. The obtained results demonstrate the high stability of carbonate rocks during short hydrogen storage cycles and imply that the reaction of the carbonate minerals with H-2 is very weak within the conditions investigated in this research. This work supports the utilization of carbonate reservoirs for UHS and can be a suitable experimental framework to assist in evaluating the hydrogen reactivity to carbonate reservoirs.