The mechanism for pore-throat scale emulsion displacing residual oil after water flooding

The reservoir characteristics and fluid property of Daqing Oilfield was taken as the research platform. The emulsion was prepared by core displacement experiment. The stability of emulsion was analyzed by measuring the Zeta potential at different emulsifier concentrations. The emulsion viscoelasticity was also measured in different water cut stage. Displacement experiments of emulsion and surfactant flooding (poor emulsification) at the same interfacial tension were conducted, and the displacement efficiency of pore-throat scale emulsion (particle size greater than throat diameter but less than pore diameter) was studied. Using a visual sand packed model, displacement experiments allowed for the observation of the pore-throat scale emulsion displacing oil drop and columnar residual oil, and the deformation and migration process of residual oil were analyzed. The mechanism of pore-throat scale emulsion displacing residual oil was studied. The results show that with the emulsifier concentration increases, the absolute value of emulsion Zeta potential increases, and the stability of emulsion increases, the stability of pore-throat emulsion is preferably. When the water cut is 63.2%, the emulsion viscoelasticity is most favorably. When the emulsifier concentration is 0.4%, the emulsion flooding can enhance recovery efficiency by 9.84% compared to surfactant flooding with the same interfacial tension. The viscoelastic deformation of the pore-throat scale emulsion can pull the oil drop and columnar residual oil, and the residual oil can migrate.