Fabrication and Mechanism Study of the Fast Spontaneous Emulsification of Crude Oil with Anionic/Cationic Surfactants as an Enhanced Oil Recovery (EOR) Method for Low-Permeability Reservoirs

An emulsion that can be fast and spontaneously formed in reservoirs will be greatly beneficial to the oil recovery improvement in low-permeability reservoirs. Herein, an ultralow interfacial tension spontaneous emulsification (SE) system consisting of a novel anionic alkyl polyglucoside sodium hydroxypropyl sulfonate surfactant (APGSHS) surfactant and a cationic cetyltrimethylammonium bromide (CTAB) surfactant was proposed and studied for low-permeability reservoirs. The spontaneous emulsions were characterized in terms of morphology and size distribution of droplets. Multiple-light scattering method was applied to evaluate the stability and dynamic instability mechanism of O/W emulsions. In addition, the viscoelasticity and shear-recovery performance of emulsions were also investigated. The combined SE systems can form the spontaneous emulsions via once bottom-up cycle, and the average droplets size of optimum emulsion with 6:4 molar ratio is ∼0.2 μm, which is small enough to migrate in the porous media at low-permeability reservoirs. Besides, the coalescence and creaming of oil droplets, as well as clarification thickness, are well-deferred. The viscoelasticity and shear-recovery capacity can also be improved with the presence of combined SE systems. The efficient interfacial activity and emulsion performances can be attributed to the strong electrostatic attraction between anionic and cationic surfactants, which enables the formation of a tighter arrangement film on an oil/water interface. Ultimately, the core flooding experiments show that the optimum SE system can effectively enhance oil recovery by 14.14% of the initial oil in place and significantly decrease the injected pressure. Hence, the newly formulated spontaneous emulsification system with anionic/cationic surfactants exhibit remarkable performances and can be used as an ideal candidate for EOR in low-permeability reservoirs.