Effect of pressure on the optimal salinity point of the aqueous phase in emulsion formation

•Increasing the salinity, at high pressure, to an optimal salinity, salting-in effect increases the stability of the emulsion.•Increasing the aqueous phase salinity, at high pressure, to an optimal salinity, salting-in effect increases the stability of the emulsion.•When the salinity exceeds to an optimal salinity, the salting-out effect reduces the stability of the emulsion.•At high pressure the salting-out effect occurs at lower salinity. In the interaction between the injected fluid and the produced fluid, emulsion formation is a common phenomenon. It can be important to evaluate the stability of the emulsion formed under reservoir pressure and the effect of salinity of injected water on this stability. In this study, the effect of aqueous phase salinity and pressure on the emulsion formation and stability have been investigated. The results showed that with increasing emulsion formation pressure from ambient pressure to 1000 psi, by considering distilled water as the aqueous phase the average droplets area of water in oil decreased from 157 μm2 to 129 μm2 and caused an increase in the stability of the emulsion. in ambient conditions, increasing the salinity of the aqueous phase from 4167 ppm to 41671 ppm with salting-in effect reduced the average droplet size from 144 μm2 to 92 μm2. At 1000 psi, reducing the salinity of the aqueous phase from 41671 ppm to 13890 ppm reduced the average droplet size from 246 μm2 to 92 μm2 and with increasing salinity of the aqueous phase from this value, the salting-out effect reduced the stability of the emulsion. As the salinity of the aqueous phase increases to a certain extent, the stability of the emulsion increases, so that by the salinity of the aqueous phase exceeds this value, the stability of the emulsion reduces. In this paper, this specific value of aqueous phase salinity, which forms the most stable emulsion, is called the optimal salinity of the aqueous phase. The results of this paper showed that increasing the emulsion formation pressure, reduces the optimal salinity of the aqueous phase.