Emulsion, as an oil displacement and conformance control system, provides essential contribution for enhanced oil recovery (EOR). However, conventional flooding systems, which form large emulsion droplets compared to the pore size of porous media in formation, usually encounters problems including high capillary pressure and poor displacement efficiency in low permeability reservoirs. Thus, it is necessary to find a new flooding system that has high displacement efficiency and no capillary pressure.

In our reseach, effects of combined surfactant and alkali on interfacial tension and spontaneous emulsification capacity for the surfactant solution were evaluated to determine the optimum formula of the flooding system. Then, the oil/water interfacial rheology and environmental influence on the spontaneous emulsion stability were performed to study the enhanced mechanism of spontaneous emulsification system. It was proposed that the solution with alkali and surfactants not only could achieve ultra-low interfacial tension, but also exhibited an excellent spontaneous emulsification behavior at a reservoir temperature of 45 °C. The average size of formed spontaneous O/W emulsion droplets was about 0.2 μm which was smaller than average size of the low permeability throats. The presence of the optimum system can further improve the interfacial rheological properties. Ultimately, the oil displacement tests, using outcrop cores with permeability in the range of 25-35 mD, indicating that EOR slug can improve approximately 12.4% as compared to the initial oil in place (IOIP) through the strikingly spontaneous emulsification flooding after water flooding, better than that of the conventional surfactant flooding. The laboratory research suggested that the newly formulated spontaneous emulsification system can be applied as an ideal EOR system and efficiently overcome the constraint of high capillary pressure in conventional chemical flooding for low permeability reservoirs.

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