Effects of Na⁺, K⁺, Ca²⁺, and Mg²⁺ cations on CO₂–brine interfacial tension under offshore storage conditions

Abstract

Abstract The laboratory determination of CO 2 ‐brine interfacial tension is very important for estimating the storage capacity of saline aquifers during the CO 2 sequestration process. In this paper, we measured CO 2 and the brine interfacial tension using the pendant‐drop method at a temperature of 285–300 K and pressure of 3–9 MPa. The brine was composed of Na + , K + , Ca 2+ , and Mg 2+ cations with different molalities. The experimental results indicate that interfacial tension increased with temperature and salinity but decreased with pressure until it reached a plateau. At the same temperature and pressure, the plateau value increased with increasing brine salinity for all types of brines used in this work. Moreover, the plateau exists whenever the CO 2 is liquid. The interfacial tension between CO 2 and brine with bivalent cations is larger than that between CO 2 and monovalent brines. Finally, we established an empirical equation based on the relationship between interfacial tension and temperature, pressure, and salt molality grounded on experimental data, which allows the evaluation of CO 2 –brine interfacial tension values with a mean deviation of ±4 mN·m −1 . © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.