Microfluidic investigations of crude oil-brine interface elasticity modifications via brine chemistry to enhance oil recovery

Abstract

Waterflooding has been widely adopted as an improved oil recovery technique since water is, in general, inexpensive and readily available. More recently, low salinity waterflooding (LSW) has been applied to oil production. LSW has successfully demonstrated higher recovery efficiencies than conventional water flooding, yet the underlying mechanism is still quite unclear. Extensive research has focused upon rock-fluid interactions under low salinity conditions, however very little work has considered interactions between oil and brine and how fluid-fluid interfacial properties are influenced by brine salinity and composition. To fill this gap, we have developed a microfluidic device for multiphase interfacial testing with length scales comparable to the pore scale of oil reservoir rocks. Unlike conventional core flooding tests, fluid-fluid phenomena can be easily visualized within microfluidic devices via optical microscopy. Oil snap-off, a phenomenon that represents a major dispersion mechanism, occurs when crude oil flows through porous media in the reservoir and induces trapping hysteresis, can be investigated within a well-controlled microfluidic flow-focusing geometry. The size of formed droplets is examined as a measure of the resistance to snap-off. It has been previously demonstrated that snap-off events are influenced by brine chemistry, oil composition, and the interaction time between crude oil and brine. Here, we show that asphaltenes in the oil phase contribute directly to the development of the elasticitic film. We also propose the reduction of interfacial elasticity by other polar components, such as naphthenic acids, which counteract asphaltene behavior over different time scales. The contribution of these effects on interfacial elasticity is shown to be mediated by both the composition and concentration of brine and oil.