Effect of formation water salinity on interfacial tension of reservoir fluids

The interaction of surface-active species within crude oil with ions in the aqueous phase can have a major influence on the interfacial tension (IFT) between these two phases. Herein, the influence of salinity on IFT is investigated systematically. Brines with different salinities, including seawater and reservoir formation water, are considered. The measurements clearly show distinct IFT trends depending on the composition and concentration of salts in the aqueous phase as well as on the crude oil chemical species, as represented by the API values. The results show that complex brine systems have a stronger effect on IFT than individual single salt brine systems. It is possible to derive distinct additive correction factors for the respective tested brine systems based on the averaged values of deviation from the respective cases in deionized water. On average for the tested 10 oils, and in comparison to measurements in DI water, IFT was reduced by 3.4 mN/m in 100 kppm CaCl2 solution, by 5.3 mN/m in 100 kppm NaCl solution, by 6.8 mN/m in formation water and by 8.2 mN/m in seawater.

Automated summary

The study systematically investigates the influence of salinity on interfacial tension (IFT) and finds that complex brine systems have a stronger effect on IFT than individual single salt brine systems. Additive correction factors can be derived for different brine systems, providing insight into the impact of different components on IFT.