Microfluidic Investigation on Interfacial Properties of Crude Oil-Brine Varying Brine Salinity and Composition

Low salinity water-flooding has been identified as an effective Enhanced Oil Recovery (EOR) method, yet the underlying mechanism remains controversial. Extensive studies have been performed on the influence of rock-brine interactions, but very little work has focused upon obtaining a solid understanding of the interactions between oil and brine and how fluid-fluid interfacial properties are influenced by various brine salinity and composition. Microfluidic devices are simple and inexpensive to fabricate and are shown here to serve as a unique platform for these investigations. We report upon the development of a microfluidic device for multiphase interfacial testing with length scales comparable to the pore sizes of oil reservoir rock.  Unlike conventional core flooding tests, however, fluid-fluid phenomena can be easily visualized within microfluidic devices under a microscope.  Oil snap-off phenomenon was controlled within a microfluidic flow-focusing geometry. The size of the generated droplets are examined as a measure of interfacial stability, or the resistance to snap-off.  Our results indicate that suppressed snap-off, and therefore a more continuous oil phase, can be observed when the brine with lower ionic strength and monovalent cations is employed.  Polar fractions in crude oil, such as asphaltenes are believed to be responsible for the build-up of the interfacial visco-elasticity, which is mediated by the ionic strength and nature of the brine, leading to increased oil phase stability.