Molecular dynamics simulations of the interfacial tension and the solubility of brine/H₂/CO₂ systems: Implications for underground hydrogen storage

The interfacial tension (IFT) between the reservoir fluids and the solubilities of the injected hydrogen and cushion gas in the underground brine plays a critical role in the security and efficiency of the trapping mechanisms associated with underground hydrogen storage (UHS), but its behavior at the molecular level is still poorly understood. This study utilizes molecular dynamics simulations to provide insights into the prevailing interactions associated with the interfacial characteristics and the solubilities of hydrogen and CO₂ (used as a cushion gas) in brine at high-pressure, high-temperature, and various salt and CO₂ concentrations. The study reports the solubilities of H₂ and CO₂ in the ternary brine/H₂/CO₂ systems for the first time and correlates the findings with UHS implementations. Results show that the increase in the CO₂ concentration reduces the IFT due to the CO₂-brine alike interactions. Besides, H₂ and CO₂ molecules trapped by brine hydrogen bonds were quantified to evaluate the solubility of the injected fluids in brine during UHS schemes.