Insights into Enhanced Oil Recovery by Viscosity Reduction Combination Flooding System for Conventional Heavy Oil Reservoir

To settle the problems of high energy consumption and carbon emissions in the thermal recovery of heavy oil, the viscosity reduction combination flooding (V-RCF) method is proposed to enhance oil recovery for conventional heavy oil reservoirs. The performance of the viscosity reduction combination flooding (V-RCF) system composed of polymer, emulsifying surfactant, and ultra-low interfacial tension surfactant was evaluated. The interfacial tension between oil and water continues to be maintained at 10−3 mN/m as the concentration of ultra-low interfacial tension surfactant(L) increases. The viscosity reduction rate of the V-RCF system reaches over 95%. A series of parallel sand pack flooding experiments were carried out to investigate enhanced oil recovery. The enhanced oil recovery (EOR) efficiency of the V-RCF under various injection modes was compared, and the best injection mode was suggested. The incremental oil recovery of the V-RCF system under multiple slug injection modes is higher than that under single slug injection mode. The optimum slug injection sequence of the V-RCF system is injecting a polymer-emulsifying surfactant(P+R) slug firstly, and then, injecting a polymer-ultra-low interfacial tension surfactant(P+L) slug. The optimum slug size ratio of polymer-emulsifying surfactant(P+R) slug and polymer-ultra-low interfacial tension surfactant(P+L) slug is 2:1. The microfluidic flooding results have further confirmed that the best recovery rate is achieved when the slug ratio is 2:1 from a microscopic perspective.