Scott Higgs, Ying Da Wang, Chenhao Sun, Jonathan Ennis-King, Samuel Jackson, Ryan Armstrong, Peyman Mostaghimi

Hydrogen storage in subsurface aquifers or depleted gas reservoirs represents a viable seasonal and/or long-term energy storage solution. However, currently, there is a scarcity of subsurface petrophysical data for the hydrogen system, limiting modelling work and industrial rollout. In this work, we address the knowledge gap by determining the wettability and Interfacial Tension (IFT) of the hydrogen-brine-quartz system using a multi-modal, in-situ approach. We utilise the captive bubble, pendant drop and in-situ 3D micro-Computed Tomography (CT) methods to rigorously characterise a hydrogen-brine-Bentheimer rock system, applicable to high quartz sandstone storage systems generally. The captive bubble method determined the effective contact angle ranged between 29°-39° for pressures 6.89-20.68MPa and salinities from distilled water to 5000ppm NaCl brine. In-situ methods confirmed the water-wet system with the mean of the macroscopic and apparent contact angle distributions being 39.77° and 59.75° respectively. Further confirmation of the water-wet system was provided by curvature analysis of fluid clusters. The pendant drop method determined that IFT decreased with increasing pressure in distilled water from 72.45 mN/m at 6.89MPa to 69.43 mN/m at 20.68MPa. No correlation was found between IFT and salinity for the 1000ppm and 5000ppm brines. Our fundamental studies provide insights into the physics of hydrogen wetting in multiphase environments of subsurface reservoirs. With this, we can make informed estimates of relative permeability and capillary pressure for the hydrogen-brine system to model the storage capacity and withdrawal rate of hydrogen in target reservoirs.