Experimental Study on the Effect of Asphaltene Concentration and Water-soluble Divalent Ions on the Interfacial Tension of Heptol/brine System

Interfacial tension (IFT) is one of the most important parameters that directly affects the capillary forces, which affects oil recovery. This research investigates the effects of asphaltene concentration and water-soluble divalent ions on IFT. A mixture of toluene and n-heptane, which is called heptol, is used as the model oil, and then asphaltene was added into Heptol to study its effect on the surface-active properties of the model oil. Brine in a salinity of sea water (SW) with a concentration of 40,000 ppm was considered as the base aqueous phase. A diluted brine with a concentration of 4000 ppm was prepared as a low salinity water (LSW), and a concentrated 80,000 ppm aqueous solution is considered high salinity water (HSW). Afterwards, the dynamic IFT of the oil phase/aqueous phase interface was measured using the pendant drop method. Results show that with the increase in the asphaltene concentration, IFT of heptol/brine system was decreased. The lowest value of IFT was observed in the salinity of 40,000 ppm. This may show an optimum salinity range to facilitate migration of asphaltene molecules into brine/heptol interface, which led to an IFT reduction from 23 to 16 mN/m. Results indicated that an asphaltene concentration of 0.5% can be was considered as the critical micelle concentration. At the end, the effect of divalent ions, i.e. calcium, magnesium and sulfate ions in the aqueous phase was investigated, and it is shown that the calcium ion has a larger effect on IT reduction compared to the magnesium and sulfate ions.