Microfluidic visualization of in-situ emulsification during surfactant flooding

Abstract

Surfactant plays a crucial role in the chemical enhanced oil recovery (cEOR) process, and in-situ emulsification is regarded as one of the mechanisms for surfactant flooding. However, no direct evidences are available so far to show how emulsions are generated in porous media, and how emulsification is essential for cEOR. To address these issues, binary mixtures of several currently-used sulfonate surfactants, S_H5, S_H6, and S_HZ, were formulated with connate brine to displace crude oil in both 2D microfluidic chips and 3D glass beads porous media, as well as artificial cores. It was found that both “oil-in-water” (O/W) and “water-in-oil” (W/O) macroemulsions can be formed in-situ inside the porous media, and they improve oil recovery mainly through breaking residual oil into small drops and improving mobility ratio, which can significantly reduce the residual oil saturation by up to 12.8% in 2D microchips. The in-situ emulsification in 3D glass beads medium can get oil recovery factor up to 15% over water flooding. In-situ formulation of microemulsion was also observed in microfluidic flow tests. Part of the oil phase is emulsified into microemulsions that are present in the middle phase, further mobilizing the oil trapped downstream, lowering residual oil saturation from 54.8% to 11.3% in 2D microchips, and enhancing oil recovery factor up to 25% in core flooding test. These findings advance insightful understanding of in-situ emulsification during surfactant flooding process under simulated oil reservoir condition, offering real-time evidence of how both macro- and micro-emulsions formation help for cEOR.