Experimental study on the mechanism of enhancing oil recovery by polymer - surfactant binary flooding

Aiming at the development situation of the Xinjiang oil field, the mechanism of enhancing oil recovery by the Polymer-Surfactant Binary Flooding (SP Flooding) was studied through SP Flooding sand pack, natural core and micro model experiments, and Optimum SP Flooding formula is provided. The results show that the enhanced oil recovery by the SP Flooding increases with the increase of the viscosity ratio between water and oil or the decrease of the interfacial tension. Capillary displacement ratio can reflect the synergetic effect of viscosity and interfacial tension and help screen out the optimum formula of the SP Flooding. For Qizhong block in Xinjiang Oilfield, where the critical viscosity ratio of SP flooding solution is 2.5, the order of magnitude of the critical interfacial tension is 1×10−2 mN/m, and the order of magnitude of the critical capillary displacement ratio is 1×10−3, the optimum formula of the SP Flooding composed of 0.3% KPS-1+1 115 mg/L HPAM can enhance the oil recovery by 23.96%. The polymer in the SP Flooding system increases the viscosity of the displacement fluid, accordingly the fluidity of the aqueous phase reduces and that of the oil phase increases, and the resulting decrease of the mobility ratio can control waterflood fingering, make water absorption thickness increase, enhance sweep efficiency and thus activate the residual oil trapped in dead ends. The surfactant decreases interfacial tension, and the resulting decrease of adhesion work makes residual oil emulsified, stripped, wiredrawn and easy to move. In addition, the emulsion liquid further increases the viscosity of the aqueous phase, and with interaction of lower interfacial tension and high viscosity of the emulsion liquid, the capillary displacement ratio is greatly enhanced, which in turn improves the oil displacement efficiency by displacing isolated-island, columnar and membranous residual oil, and consequently a higher oil recovery.