Low-Shear Emulsifying System for Cold Production of Conventional Heavy Oil

Emulsification-based viscosity reduction technology is an effective cold recovery method for enhancing the recovery of conventional heavy oil. However, most conventional emulsifying viscosity reducers form oil-in-water (O/W) emulsions under high-shear conditions. In contrast, the shear rate between fluid and heavy oil in actual reservoir conditions is relatively low (<10 s–1), which may impair the emulsification and viscosity reduction efficiency. To address this challenge, an emulsifying system (CLVR) suitable for low-shear conditions was developed to enhance the mobility and recovery of conventional heavy oil. The CLVR system comprises an anionic surfactant, sodium oleate, and a nonionic surfactant, lauric diethanolamide (LDEA). The emulsification performance, interfacial tension, viscosity reduction efficiency, and emulsion stability of the CLVR system under low-shear conditions were systematically investigated. Emulsification experiments were conducted using a thermostatic shaker at 10 rpm (shear rate of 0.42 s–1) to simulate low-shear reservoir conditions. The results revealed that under the optimal formulation─a total surfactant concentration of 0.25 wt % with a sodium oleate-to-LDEA mass ratio of 8:2─the CLVR system achieved an ultralow interfacial tension of 3.1 × 10–3 mN/m and a viscosity reduction rate of 94% under low-shear conditions. Furthermore, a composite emulsifying system was developed by integrating CLVR with hydrolyzed polyacrylamide (HPAM), which concurrently increased aqueous phase viscosity, optimized the water–oil mobility ratio, and effectively suppressed viscous fingering. Both core flooding experiments and microfluidic visualization studies confirmed the remarkable synergistic effects of the composite system under low-shear conditions, yielding an incremental oil recovery of 22%. This work provides both theoretical insights and practical guidance for the rational design of efficient emulsification-based viscosity reduction systems adapted to low-shear environments, holding significant promise for the cold production of conventional heavy oil.