Visualizing in-situ emulsification in porous media during surfactant flooding: A microfluidic study.

Both oil-in-water (O/W) and water-in-oil (W/O) emulsions are formed in microchips during the surfactant flooding. Increasing SDBS concentration, migration distance, injection rate, or addition of electrolyte tends to form smaller O/W particles through snapping action at pore throat, and vice versa. Smaller size endows oil with a better mobility to go through the pore throat, and up to 24% extra emulsion can be achieved through emulsification entrainment; bigger droplets can block the dominant paths, thus improving sweep efficiency and increasing oil recovery factor up to 30% compared to waterflooding. Furthermore, W/O emulsification was found to be a time-dependent process influenced by SDBS concentration, and oil was recovered by diffusing surfactant solution into oil phase and replacing the oil-occupied space in porous media.