Interfacial Tension between CO2, Freshwater, and Brine in the Range of Pressure from (2 to 27) MPa, Temperature from (20 to 125) °C, and Water Salinity from (0 to 334 000) mg·L−1

Abstract

An extensive laboratory program was conducted for the measurement of the interfacial tension between CO2 and water or brine covering the ranges of (2 to 27) MPa pressure, (20 to 125) °C temperature, and (0 to 334 010) mg·L−1 water salinity. The laboratory experiments were conducted using the pendant drop method combined with the solution of the Laplace equation for capillarity for the profile of the brine drop in the CO2−brine equilibrium environment. The analysis of the resulting set of 378 IFT measurements reveals that: (1) under conditions of constant temperature and water salinity, IFT steeply decreases with increasing pressure in the range P < Pc and mildly decreases for P > Pc with an asymptotic trend toward a constant value at higher pressures; (2) under the same conditions of constant pressure and temperature, IFT increases with increasing water salinity, reflecting decreasing CO2 solubility in brine as salinity increases; (3) the dependence of IFT on temperature is more complex than that on either pressure or salinity, depending on the CO2 phase. For T < Tc, IFT increases with increasing temperature, and around the critical point (T ≈ Tc), IFT significantly decreases (believed to be associated with the fact that at Tc the IFT between CO2 liquid and vapor phases tends to zero) and then increases again with increasing temperature for T > Tc with an asymptotic trend toward a constant value for high temperatures. The dependence of IFT on pressure, temperature, and water salinity for CO2 and water/brine systems can be well approximated by a power function of pressure whose coefficient and exponent depend on temperature and water salinity. These results indicate that, in the case of CO2 storage in deep saline aquifers as a climate-change mitigation strategy, the formation water displacement by injected CO2 during the injection (drainage) phase of CO2 storage and the possible subsequent CO2 displacement by invading brine during the CO2 migration (imbibition) phase depend on in situ conditions of pressure, temperature, and water salinity through the effects that these primary variables have on the IFT between CO2 and aquifer brine.