Evaluating the role of rock permeability in H₂ and CH₄ migration through water aquifers

This study investigates the impact of sandstone permeability on the efficiency and feasibility of subsurface storage of hydrogen (H₂) and methane (CH₄), by analyzing gas displacement, and retention behaviour, in three sandstone formations (Bentheimer, Berea, and Scioto) under controlled core flooding experiments. Due to the low density, high diffusivity, and broad flammability range of H₂, experimental challenges arise during laboratory testing. Therefore, CH₄ is considered as a potential analog to evaluate whether it exhibits comparable displacement behaviour under adjusted flow conditions. Additionally, CH₄ can serve as a cushion gas during underground hydrogen storage.Unlike previous studies focused on single-rock systems, this work systematically compares gas displacement behaviour across sandstone formations with distinctly different permeability ranges under both matched and unmatched capillary number conditions. By adjusting the CH₄ injection rate to align with the capillary number of H₂, the study evaluates whether CH₄ can reproduce displacement behaviour comparable to H₂ under capillary-controlled flow conditions.Accordingly, a series of core flooding experiments were conducted using Bentheimer, Berea, and Scioto sandstones, which have varying permeabilities of 2704 md, 140 md, and 1.7 md, respectively.The results demonstrated that sandstone permeability significantly influences gas displacement efficiency and storage potential. Bentheimer exhibited the fastest gas migration and highest gas storage capacity, making it more suitable for H₂ storage and withdrawal. In contrast, Scioto showed the lowest gas storage capacity and longest breakthrough time. Berea showed an intermediate displacement behavior, with characteristics falling between those of Bentheimer and Scioto. Initially, at the same flow rate (2 cc/min), CH₄ exhibited higher saturation than H₂ due to weaker capillary resistance. However, when CH₄ flow rate was reduced to 1.32 cc/min, its behavior was similar to H₂, confirming that CH₄ and H₂ are non-wetting phases. These findings highlight the importance of permeability and capillary number adjustments in experimental research on underground hydrogen storage.