Investigation of microflow mechanisms and emulsion size distribution in porous media

Crude oil in underground porous media can be emulsified by surfactants, which can lead to improved oil recovery. However, there have been limited investigations revealing the interactions between emulsions and grains and comparing the influence of different factors on the distribution of emulsions in porous media at the pore scale. In this study, a solution containing surfactant was injected into an oil-saturated microchip with heterogeneous pore geometries. A series of tests were conducted by varying the injection rate, surfactant concentration, oil viscosity, and displacing phase viscosity. Qualitative analysis of flow mechanisms and quantitative analysis of the distribution of emulsions were performed through pore-scale snapshots. The results demonstrate that emulsions undergo deformation, breakup, and retention in porous media. Furthermore, new micro-interactions between emulsion droplets and grains are discovered, including the impact effect, cutting effect, and the synergy of both effects. A high flow rate of the displacing phase promotes the formation of more and smaller emulsions, while a low flow rate encourages flow diversion. An increase in oil viscosity and a decrease in surfactant concentration are not conducive to the formation of emulsions. However, an increase in the displacing phase viscosity promotes the formation of emulsions and flow diversion. The experiments provide detailed insights into the flow behaviors of emulsions at pore scale and offer valuable information for surfactant flooding.