Integrated Characterization of Drainage Mechanism in Sandstone and Carbonate Rocks for H2-Brine Systems: Application to Underground Hydrogen Injection

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Abstract
Underground hydrogen storage (UHS) is a promising option for large-scale energy storage to support the hydrogen (H2) economy; however, its effective implementation requires understanding hydrogen–brine multiphase flow behavior in geological rocks under pore-scale heterogeneity. This study presents an integrated experimental investigation of H2-brine drainage in sandstone and carbonate rocks using capillary pressure, nuclear magnetic resonance (NMR), and electrical resistivity measurements. Pore-scale drainage mechanisms are inferred from NMR T2 relaxation distributions rather than direct pore-scale imaging. Capillary pressure experiments showed decreasing water saturation with increasing pressure, indicating hydrogen invasion, with irreducible water saturation reflecting macropore dominance. Carbonate samples exhibited lower irreducible water saturation (31.9–34.5%) than sandstone samples (36.3–41%). Electrical resistivity increased nonlinearly with decreasing saturation. NMR revealed preferential macropore drainage followed by limited micropore drainage. These observations provide experimental insight into equilibrium H2-brine drainage behavior and highlight the importance of pore-scale heterogeneity for future multiphase-flow characterization and reservoir modeling relevant to underground hydrogen storage.

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