Assessment of wettability and rock-fluid interfacial tension of caprock: Implications for hydrogen and carbon dioxide geo-storage

Underground hydrogen (H-2) storage (UHS) and carbon dioxide (CO2) geo-storage (CGS) are prominent methods of meeting global energy needs and enabling a low-carbon global economy. The pore-scale distribution, reservoir-scale storage capacity, and containment security of H(2 )and CO2 are significantly influenced by interfacial properties, including the equilibrium contact angle & nbsp;(theta E) and solid-liquid and solid-gas interfacial tensions (gamma(SL) and gamma(SG)). However, due to the technical constraints of experimentally determining these parameters, they are often calculated based on advancing and receding contact angle values. There is a scarcity of theta(E),gamma(SL), and gamma(SG) data, particularly related to the hydrogen structural sealing potential of caprock, which is unavailable in the literature. Young's equation and Neumann's equation of state were combined in this study to theoretically compute these three parameters (theta(E), gamma(SL), and gamma(SG)) at reservoir conditions for the H-2 and CO2 geo-storage potential. Pure mica, organic-aged mica, and alumina nano-aged mica substrates were investigated to explore the conditions for rock wetting phenomena and the sealing potential of caprock. The results reveal that theta(E) increases while gamma(SG) decreases with increasing pressure, organic acid concentration, and alkyl chain length. However,gamma(SG) decreases with increasing temperatures for H-2 gas, and vice versa for CO2. In addition, theta(E) and gamma(SL) decrease, whereas gamma(SG) increases with increasing alumina nanofluid concentration from 0.05 to 0.25 wt%. Conversely, theta(E) and gamma(SL) increase, whereas gamma(SG) decreases with increasing alumina nanofluid concentration from 0.25 to 0.75 wt%. The hydrogen wettability of mica (a proxy of caprock) was generally less than the CO2 wettability of mica at similar physio-thermal conditions. The interfacial data reported in this study are crucial for predicting caprock wettability alterations and the resulting structural sealing capacity for UHS and CGS.(c) 2022 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).