Interfacial tensions of (brine + H2 + CO2) systems at gas geo-storage conditions

In hydrogen geological storage, cushion gas has vital role to retain adequate reservoir pressure to keep the hydrogen withdrawal stable. Presence of the cushion gas in the storage reservoir can affect the flow characteristics of hydrogen during injection and production cycles. One of the most crucial parameters that control the fluids flow in porous media is interfacial tension (IFT) between fluids. However, the literature data lacks in terms of IFT between cushion gas mixed with hydrogen and brine at geo-storage conditions. In this study, the pendant drop method was used to measure the IFT of (brine + H-2 + CO2) system at different CO2 fractions as cushion gas, reservoir temperature, reservoir pressure, and water salinity. The results showed that the IFT reduced with increasing CO2 percentage. Moreover, IFT declined when pressure went up gradually. This pattern was almost linear at lower proportion of CO2; however, a nonlinear trend was observed at higher percentage of CO2. In addition, at constant pressure, IFT decreased with temperature. These results also demonstrated that the IFT increases linearly with brine salinity. This work thus presents new dataset for hydrogen geological storage projects, where large-scale hydrogen with CO2 (as a cushion gas) can be stored in geological formations.