Geochemical Stability of Carbonate Reservoirs for Safe and Efficient Underground Hydrogen Storage: A Case Study in North Dakota's Red River Formation

Abstract The global shift toward sustainable energy solutions has intensified interest in large-scale energy storage systems, with Underground Hydrogen Storage (UHS) in depleted oil and gas reservoirs has emerged as a viable option. A critical challenge in UHS is understanding the geochemical and petrophysical interactions between hydrogen, reservoir rock, and brine, which directly impact the safety and efficiency and long-term stability of storage operations. This study investigates the effects of hydrogen exposure on the geochemical and petrophysical properties of carbonate reservoirs through experimental analysis of core samples from the Red River Formation. Core samples from three wells (W13756, W13927, and W14075) were exposed to hydrogen at 2500 psi and 150°C for 30 days to simulate reservoir conditions. Core samples from three wells (W13756, W13927, and W14075) were subjected to hydrogen at 2500 psi and 150°C for 30 days to simulate reservoir conditions. The experiments revealed significant porosity and permeability changes. NMR relaxometry indicated porosity increases of 133.6% (3.39% to 7.92%) for Well 13756, 18.2% (9.25% to 10.93%) for Well 13927, and 20.6% (9.14% to 11.02%) for Well 14075. Correspondingly, permeability increased by 25.76% (0.66 mD to 0.83 mD) for Well 13756, 12.71% (0.80 mD to 0.9017 mD) for Well 13927, and 25.4% (0.05 mD to 0.0627 mD) for Well 14075. Mineralogical analysis via X-ray diffraction (XRD) highlighted significant transformations. For Well W14075, dolomite content decreased from 69.6% to 29.91%, accompanied by the formation of 43.14% vaterite and 25.10% calcite. Well W13927 exhibited a reduction in dolomite from 31.98% to 26.90%, with 3.78% calcite, 0.50% vaterite, and 0.42% aragonite emerging. In contrast, Well W13756 showed an increase in dolomite from 49.33% to 84.24%, alongside 6.31% vaterite and 0.67% calcite formation. These mineralogical changes indicate precipitation-dissolution dynamics, further corroborated by SEM observations of newly formed carbonate phases and distinct pore structure modifications.The results underscore the significant impact of hydrogen-rock interactions on the geochemical, petrophysical, and mechanical characteristics of carbonate formations. Increased porosity and permeability improve hydrogen injectivity and flow, while mineralogical changes and enhanced mechanical properties suggest improved structural stability under UHS conditions. These findings highlight the suitability of carbonate reservoirs, like the Red River Formation, for long-term hydrogen storage while providing critical insights into optimizing storage performance. This study advances the understanding of hydrogen storage dynamics in carbonate formations, offering valuable implications for developing safe, efficient, and sustainable UHS systems.