Oil-water interactions in porous media during fluid displacement: Effect of potential determining ions (PDI) on the formation of in-situ emulsions and oil recovery

Emulsification is a naturally occurring phenomenon during the multiphase flow. The amount of emulsion, its composition and rate of degradation can significantly affect the flow properties and subsequent oil recovery. In addition, fluid-fluid interactions were suggested as a controlling mechanism for enhancing the oil recovery by modified salinity brines. In this study, we have used high-resolution microtomography to visualise emulsions formed in heterogeneous carbonate rocks by seawater and ion-tuned brines. Additionally, interfacial tension and emulsion stability were studied in a laboratory environment to develop further understanding of the effect of naturally occurring (in absence of surfactant agents) in-situ emulsions on Enhanced Oil Recovery (EOR) at porescale. Our results show that emulsions that are formed in pores have varying compositions depending on pore geometries, wetting properties of the rock surface and ionic composition of the injected brines. In-situ emulsification has shown to be a contributing factor to the oil recovery enhancement, however, other mechanisms, such as wettability alteration plays an important role. Emulsion cluster sizes show log bimodal distribution and injection of ion tuned brines mostly contribute to improving the connectivity between the clusters and subsequent sweep efficiency of the waterflooding.