Performance of a good-emulsification-oriented surfactant-polymer system in emulsifying and recovering heavy oil

Considering the significant importance of emulsification for heavy oil recovery, a good-emulsification-oriented (GEO) (rather than the conventional ultralow interfacial tension (IFT) oriented) surfactant-polymer (SP) system was employed to remove heavy oil. Specifically, the emulsification behavior and viscosity-reduction property of heavy oil in porous media were first studied by flood tests. Then, such a GEO SP was used to displace heavy oil for recovery measurement. It is found that first, as migration increases in porous media, the in situ emulsified oil droplets evolve into smaller and more uniform droplets (without coalescence), thus, exhibit self-adjustment ability to match with, and plug, the pores. An increase in surfactant content and seepage velocity also makes the emulsion's particles smaller and more uniformly distributed. Second, such oil-in-water emulsification indeed helps to reduce heavy oil viscosity in porous media and there is an optimal surfactant content for such viscosity reduction: The lower the water cut, the greater the optimal surfactant content, the worse the viscosity-reduction effect. Third, on its own, the GEO surfactant performs very poorly in recovering heavy oil and is even worse than the single polymer; therefore, such a surfactant should be jointly used with a polymer in an SP system instead of on its own, but an excessive surfactant content in the SP seems to hinder the recovery, while the large slug size tends to contribute significantly to an improved oil recovery.