Synergistic Collaboration between a Viscosity Reducer and a Surfactant for in Situ Emulsion Formation to Enhance Heavy-Oil Recovery

Abstract

In situ emulsion formation is an effective nonthermal method to improve conventional heavy-oil recovery. In this paper, a newly designed viscosity reducer (TPVR7) and a high-performance surfactant (dioctyl sodium sulfosuccinate, DSS) for enhanced conventional heavy-oil recovery have been introduced and evaluated. A dewatering rate test, emulsion droplet size measurement, multiple-light scattering, and interfacial tension measurement are carried out to evaluate the synergistic effect of the viscosity reducer and the surfactant on the emulsion stability and efficiency in enhancing heavy-oil recovery. The results show that adding a surfactant can significantly increase the emulsion stability by decreasing the size of the emulsion droplet and forming a tighter interfacial film. The optimum viscosity reducer–surfactant system is formulated as TPVR7-0.5% + DSS-0.5%. With the optimum system, the viscosity of heavy oil decreased from 350 to 9 mPa·s. The equilibrium interfacial tension of the oil/TPVR7-0.5% + DSS-0.5% solution is ∼0.092 mN/m, much lower than that of the oil/TPVR7 solution. The mechanisms of synergistic collaboration between the viscosity reducer and the surfactant include enhanced emulsion stability, viscosity reduction, and interfacial tension reduction. The sand-pack flooding experiments show that a viscosity reducer and surfactant could improve heavy-oil recovery by 21.89% after water flooding at the optimum concentration, which indicates that viscosity reducer and surfactant flooding has great potential to enhance heavy-oil recovery.