Direct Insight into the Cause and Time Evaluation of Spontaneous Emulsification of Water in Crude Oil during Low Salinity Waterflooding Using Microfluidic Model

In prior research, the formation of emulsions has been proposed as an effective mechanism to enhance the recovery during the injection of low salinity water (LSW) from different points of view, such as improving the mobility ratio, changing the wettability, and swelling the oil layer adhered to the rock surface. The spontaneous emulsification process and its causes are still an unclear area of LSW studies. To study the formation of the emulsion as an active mechanism in the LSW injection, it is necessary to pay attention to the time required to form these emulsions spontaneously and places prone to their formation. In addition to the visual investigation of the spontaneous formation of emulsions, the current study also aimed at evaluating the time required for their spontaneous formation and identifying the main drive force to form these microsized dispersions. To this end, water-in-oil emulsions were prepared naturally without the use of surfactants to simulate spontaneous emulsification. Also, stability analysis by droplet size measurement was used as an observational criterion to evaluate different brines' tendencies to form expected in situ emulsions in a porous medium. However, for visual investigation of emulsification in porous media, glass micromodels were used. The stability analysis results showed that the increase in the emulsions' instability occurred with the increase of the ionic strength of the aqueous phase. In the micromodel experiments, the spontaneous emulsification was confirmed when low salinity water was injected. Moreover, the micromodel experiments revealed that the emulsions did not start to form immediately but formed within a week and reached a maximum approximately after 10 days. It can be concluded that the oil layer can act as a semipermeable layer and water inverse micelles enter the oil layer by diffusion. The rate of emulsion formation is controlled by diffusion induced by the osmosis imbalance condition in LSW injection.