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

Abstract

Underground hydrogen (H 2 ) storage (UHS) and carbon dioxide (CO 2 ) 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 CO 2 are significantly influenced by interfacial properties, including the equilibrium contact angle ( θ E ) and solid-liquid and solid-gas interfacial tensions ( γ S L and γ S G ). 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 θ E , γ S L , and γ S G 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 ( θ E , γ S L , and γ S G ) at reservoir conditions for the H 2 and CO 2 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 θ E increases while γ S G decreases with increasing pressure, organic acid concentration, and alkyl chain length. However, γ S G decreases with increasing temperatures for H 2 gas, and vice versa for CO 2 . In addition, θ E and γ S L decrease, whereas γ S G increases with increasing alumina nanofluid concentration from 0.05 to 0.25 wt%. Conversely, θ E and γ S L increase, whereas γ S G 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 CO 2 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. • The equilibrium contact angle ( θ E ) increases with pressure and organic concentration but decreases with temperature. • The solid-gas interfacial tension ( γ S G ) decreases with pressure and organic concentration but increases with temperature. • The solid-liquid interfacial tension ( γ S L ) and θ E decreases, whereas γ S G increases with increasing alumina nanofluid concentration. • Mica hydrogen wettability is less than mica CO 2 wettability in all physio-thermal conditions.