Synergy of alkali and surfactant in emulsification of heavy oil in brine

The emulsification and entrainment of crude oil into displacing water is one of the mechanisms of alkaline flooding for conventional oil. If this mechanism is applied in heavy oil reservoirs, the flow of viscous oils and subsequently the oil recovery can be greatly improved. The formation brine of heavy oil reservoirs usually has a high salinity and high content of multiple cations that make the in situ emulsification of heavy oil a challenge.In this work, a heavy oil of 14° API is used to study the mechanism of emulsification of heavy oils in brine under slight interfacial disturbance. Emulsification tests and interfacial measurements are carried out to screen alkalis and surfactant additives for emulsifying the oil in the diluted formation brine. The results show that if only alkali or only surfactant is added into the brine, emulsification of the oil in brine cannot be triggered. When alkali (Na2CO3) and very dilute surfactant are used together, the oil can be easily emulsified. The synergy of alkali and surfactant in emulsifying the heavy oil in brine is investigated by measuring the dynamic interfacial tension (IFT) and zeta-potential of emulsions. It is found that the interaction of added surfactant and in situ surfactant from the reaction of alkali and organic acids in oil can significantly reduce the dynamic interfacial tension between oil and water and increase the surface charge density of emulsions. The synergistic enhancement between alkali and surfactant is the key mechanism of emulsifying heavy oils in brine under slight interfacial disturbance.