Effect of temperature on interfacial properties of CO₂/H₂ mixtures contacting with brine and hydrophilic silica by molecular dynamics simulations

Abstract

Underground H₂ storage (UHS) is a promising technology to achieve large-scale, long-term H₂ storage. Using CO₂ as a cushion gas to maintain the pressure of the reservoir and withdraw stored H₂ in the saline aquifer simultaneously enables the implementation of UHS and underground CO₂ storage (UCS). The difference in the molecular properties of CO₂ and H₂ leads to distinct interfacial behavior when in contact with the brine and rock, thereby affecting the flow patterns and trapping mechanisms of gases in geological formations. Accurate prediction of the interfacial properties of CO₂, H₂, and the mixtures when interacting with brine and rock is crucial to minimizing the uncertainties in UHS and UCS projects. In this study, molecular dynamics (MD) simulations are performed to predict the interfacial tension, surface excess, bubble evolution, and contact angle of CO₂, H₂, and the mixtures at 10 MPa and 300–400 K. The MD results show that the interaction of CO₂ with H₂O and hydrophilic silica is considerably stronger than that of H2. The interfacial tension reduces linearly with the temperature in H₂-dominated mixture systems, and the surface adsorption of H₂ can diminish in a CO₂-dominated system or at high-temperature conditions. The hydrophilic silica is more CO₂-wet than H₂-wet, and the attached CO₂ bubble is more easily disconnected. Ions and the temperature play different roles in the contact angle.