Critical parameters controlling wettability in hydrogen underground storage - An analytical study

Hypothesis: The large-scale implementation of hydrogen economy requires immense storage spaces to facilitate the periodic storage/production cycles. Extensive modelling of hydrogen transport in porous media is required to comprehend the hydrogen-induced complexities prior to storage to avoid energy loss. Wettability of hydrogen-brine-rock systems influence flow properties (e.g. capillary pressure and relative permeability curves) and the residual saturations, which are all essential for subsurface hydrogen systems. Model: This study aims to understand which parameters critically control the contact angle for hydrogen-brine-rock systems using the surface force analysis following the DLVO theory and sensitivity analysis. Furthermore, the effect of roughness is studied using the Cassie-Baxter model. Findings: Our results reveal no considerable difference between H2 and other gases such as N2. Besides, the inclusion of roughness highly affects the observed apparent contact angles, and even lead to water-repelling features. It was observed that contact angle does not vary significantly with variations of surface charge and density at high salinity, which is representative for reservoir conditions. Based on the analysis, it is speculated that the influence of roughness on contact angle becomes significant at low water saturation (i.e. high capillary pressure).