(169f) Influence of Gas-Water Interface for Underground Hydrogen Storage

Underground hydrogen storage (UHS) in porous formations is emerging as a critical component for energy storage and supply. This presentation explores the complex interactions at the gas-water interface, essential for optimizing hydrogen geo-storage. Utilizing molecular dynamics simulations, we examine key factors such as pressure, pore size, surface composition, and interfacial tension (IFT) dynamics that influence hydrogen transport and storage in subsurface conditions. The study starts with model validation and hydrogen transport behavior in organic and inorganic slit pores, revealing that H₂ molecules exhibit a preference for adsorption onto graphene over kaolinite surfaces. Despite weak interactions with both materials, the significance of surface roughness in mitigating hydrogen loss through diffusion is highlighted, especially as pore size increases and pressure decreases. At pressures above 100 atm, hydrogen transport is predominantly governed by thermal collisions, leading to minimal differences in diffusion behavior between pore types.

Further analysis focuses on the interfacial tension between pore water and hydrogen-cushion gas mixtures, critical for gas distribution within UHS systems. Our simulations of H₂–CO₂–H₂O and H₂–CH₄–H₂O systems demonstrate that increasing cushion gas concentration reduces gas-water IFT. In particular, CO₂ adsorption significantly decreases IFT, especially at concentrations up to 40%, while CH₄ exhibits a linear reduction effect. These variations are attributed to molecular orientation effects and local density distributions at the interface, which also affect hydrogen self-diffusion. The dynamics of IFT in mixtures containing H₂, CH₄, and H₂S are also investigated, revealing that even low concentrations of H₂S can significantly reduce IFT, with the effect saturating at higher concentrations. The interaction between CH₄ and H₂S at the interface further underscores the complexity of gas interactions in UHS.

Finally, the presentation discusses the wettability of subsurface minerals, which is crucial for capillary trapping and fluid transport. By decoupling the effects of in-situ conditions and surface properties, we find that quartz surface methylation and roughness play dual roles in altering wettability. The interplay between methylation degree, salinity, and pressure is shown to significantly influence quartz wettability, affecting the efficiency and safety of hydrogen storage.

These findings provide a comprehensive understanding of the gas-water interface, offering insights that are vital for the development and optimization of UHS operations.