Investigation into the Functions of Alkali and Surfactant in Chemical Flooding for Enhanced Heavy-Oil Recovery

Abstract

In this study, a comparative study of alkaline flooding and alkali-surfactant flooding were conducted for Zhuangxi heavy oil with viscosity of 325 mPa•s at 55 °C. The results of core flooding tests show that the tertiary oil recovery of alkali-surfactant flooding are lower than those of alkaline-only flooding, in spite of the coexistence of the surfactant and alkali can reduce the IFT between the heavy oil and aqueous phase to an ultralow level. Further flood study via glass-etching micromodel tests demonstrates that injected alkaline-only solution can penetrate into the oil phase and creates some discontinuous water droplet inside the oil phase that tend to lower the mobility of the injected water and lead to the improvement of sweep efficiency. While for alkali-surfactant flooding, heavy oil is easily emulsified in brine by an alkaline plus very dilute surfactant formula to form oil-in-water emulsion, and then entrained in the water phase. Therefore, viscous fingering phenomena occur during the alkali-surfactant flooding, resulting in relatively lower sweep efficiency.