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

The laboratory determination of CO2-brine interfacial tension is very important for estimating the storage capacity of saline aquifers during the CO2 sequestration process. In this paper, we measured CO2 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+, Ca2+, and Mg2+ 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 CO2 is liquid. The interfacial tension between CO2 and brine with bivalent cations is larger than that between CO2 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 CO2-brine interfacial tension values with a mean deviation of +/- 4 mN.m(-1). (C) 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.