Spontaneous emulsification induced by a novel surfactant-polymer compound system and its application to enhance oil recovery

Abstract The application of spontaneous emulsification method during oil displacement provides a low-cost and environmentally friendly approach to enhance oil recovery for unconventional reservoirs. A surfactant-polymer mixture system composed of hydrophobically modified polyvinyl alcohol (HPVA) and cetyltrimethylammonium bromide (CTAB) with the ability of spontaneous emulsification was constructed. The optimum formulation of HPVA/CTAB compound system was selected based on the spontaneous emulsification capability and emulsion stability. It is found that the system showed best spontaneous emulsification performance with the concentration of 3000 mg/L and the mass ratio of 7:3 (HPVA:CTAB). The dynamic interfacial tension between oil and water reached ultra-low level to promote oil dispersing into water spontaneously, then rose back to low level to keep the emulsion stable. The synergistic effect of compound system enhanced the intermolecular attraction between HPVA molecule and CTAB molecule, which lead to a tighter interfacial film to maintain a better stability of emulsions. For low permeability cores, displacement tests showed an additional oil recovery of 12.4% by the injection of spontaneous emulsification system. These remarkable performances enable this system an ideal candidate for oil recovery enhancement.