Effect of the 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.