Stability of oil-in-water (O/W) nanoemulsions and its oil washing performance for enhanced oil recovery

Nanoemulsions consist of small particle size, uniform dispersion, and long-term stability, making them suitable for use in enhanced oil recovery for low-permeability reservoirs. In this paper, an ultrastable oil-in-water nanoemulsion was prepared using the emulsification inverse phase method at a constant temperature. Rheology, multiple-light scattering, laser particle size analyzer, and optical microscope were used to determine the effects of the emulsifier and water content, salinity, and reservoir temperature on the stability of the prepared nanoemulsion. The oil washing performance of nanoemulsion was tested by the weight-loss method. Results show that the nanoemulsions tend to be stable with an increase in the emulsifier content (>= 8 wt. %). As the water content increases, the viscosity of nanoemulsions gradually decreases as well as its elasticity. The salinity and temperature are found to have minor effects on the stability of nanoemulsions. At the same time, the oil washing efficiency of nanoemulsion can reach as high as 83%. Hence, this study will provide theoretical supports and guidelines for the preparation of highly efficient nanoemulsion flooding systems for low-permeability reservoirs.