Emulsions for enhanced oil recovery: Progress and prospect

The objective of this review is to summarize progress in enhanced oil recovery (EOR) using emulsions. Recent developments in bulk emulsion characteristics, including emulsion phase behavior, droplet size distribution, viscosity, rheology, and interface properties, as well as the factors that affect them, are discussed. Additionally, methods for evaluating emulsion stability and factors affecting emulsion stability are discussed. The factors that affect in-situ emulsification in porous media are compared, and the two-phase flow characteristics of emulsions in pores are described. The plugging mechanism of emulsion droplets in pores and the redistribution of liquid flow caused by emulsion blockage are analyzed. Emphasis is placed on determining the effective viscosity of emulsion and calculating pressure drop along the flow path. Four models for emulsion flow in porous media are compared. The EOR mechanisms of different types of emulsions under water-wet and oil-wet conditions are summarized. Combining the results of laboratory simulations and field tests, the potential of emulsions for EOR is pointed out. However, the EOR mechanism of emulsions is complicated and remains unclear. Therefore, the future direction for further studies to effectively apply emulsion for EOR is proposed.