Phase Behavior and Physicochemical Properties of (Sodium Dodecyl Sulfate plus Brine + Propan-1-ol + Heptane) Microemulsions

Experimental investigations have been made on the phase behavior of the (sodium dodecyl sulfate + brine + propan-1-ol + heptane) microemulsion system and its stability under reservoir conditions for its use in enhanced oil recovery (EOR). An increase in salinity is found to decrease the single-phase microemulsion region as salt interacts with surfactant to reduce its activity. As salinity changes from a low to high value, a phase transition takes place from Winsor I to Winsor II via Winsor III. The temperature also induces a phase transition for low- and high-salinity microemulsion systems. With an increase in temperature, the phase transition takes place from Winsor I to Winsor III for low salinity and Winsor II to Winsor III for high salinity microemulsion systems. The solubilization parameter of oil increases with an increase in salinity, whereas that of water decreases and at optimal salinity both are same. With increasing salinity, interfacial tension (IFT) between oil and microemulsion decreases, whereas that of water and microemulsion increases. At optimal salinity, both IFT values are the same. The optimal salinity increases with increasing temperature. Interestingly the conductivity of the middle-phase microemulsion system showed maxima around optimal salinity.