Microfluidic platform to study crude oil -- brine systems

An increasing percentage of the world's oil is produced from mature fields that rely upon improved oil recovery methods. In certain instances, waterflooding with low-salinity brine has been shown to increase production over conventional methods and is being rapidly adopted as a promising improved recovery strategy. Despite its recent popularity and success, the mechanisms by which low-salinity waterflooding increases recovery efficiency remains unclear. Microfluidic flow-focusing is presented as a viable experimental platform to directly investigate the interfacial behavior and flow dynamics of oil-water systems. This platform forms oil drops via extensional flows in a manner that replicates pore-level flow dynamics and snap-off events in porous media. The motivation for developing this experimental platform is the elucidation of how snap-off is influenced by dynamic interfacial properties that evolve under static conditions as the oil ages in a brine reservoir over time. It is hypothesized that aging crude oil in low-salinity brine produces dynamic interfacial properties that suppress pore-level snap-off events. Our experimental oils consisted of two crude oil samples and a control heavy mineral oil. Na2SO4 brine was diluted with deionized water to create a range of low- to high-salinity brines. Measurements of the formed drop area captured distinct qualitative differences in snap-off events after aging in low-salinity brine when compared to high-salinity brine. Crude oils aged in low-salinity brine formed significantly larger drops, indicating that the fundamental mechanism of snap-off was affected. We hypothesize that a key interfacial property of the oil, namely the interfacial viscoelasticity, is dynamically altered during aging, resulting in snap-off suppression. Quantitative modeling of this process was performed in COMSOL to demonstrate that shear forces driving the snap-off event are substantially greater for crude oil aged in low-salinity brine and that the interface can withstand a much greater critical shear force prior to snap-off. Finally, dynamic snap-off behavior is analyzed geometrically in the context of classical Rayleigh-Plateau instability theory. Snap-off events for the model oil behave in accordance with the instability theory, while instabilities are suppressed in crude oil aged with low-salinity. The outcomes of this research demonstrate the importance of dynamic fluid-fluid properties on snap-off dynamics and suggest that interfacial phenomena are an overlooked component in the low-salinity enhanced oil recovery effect.