Experimental study on the effect of high water cut on the emulsifying properties of crude oil

Abstract

Most waterflooding oilfields have entered the high water cut stage, but significant amounts of crude oil remain in the formation. Therefore, understanding the emulsifying characteristics of crude oil with high water content is crucial. This study investigates the effects of shear time, shear rate, temperature, water content, and re-emulsification at high water content on the emulsifying properties of crude oil. Results indicate that shear time, temperature, and water content play a role in enhancing the emulsifying capacity of crude oil. Additionally, the initial water content of the emulsion affects the solubilization ability of crude oil; lower initial water content leads to stronger solubilization ability, while higher total water content leads to weaker solubilization capacity. Under an optical microscope, the morphology of the emulsion was observed, revealing that an increase in water content resulted in an increase in particle size and quantity of emulsion droplets, leading to more uniform droplets. However, at high water content, the particle size of emulsion decreased, the number of droplets decreased, and the droplets became uneven. Furthermore, the particle size of re-emulsified emulsion was smaller than that of the emulsion with the same moisture content, indicating that re-emulsification can lead to instability. The interfacial characteristics of the emulsion were also analyzed, showing that an increase in water content caused an increase in interfacial tension and expansion modulus of emulsion compared to crude oil. Finally, the study elucidates the influence mechanism of high-water content on the emulsifying performance of crude oil, which includes the destruction of molecular forces on and between interfaces, weakening the steric hindrance effect. Unstable film and non-uniform droplets can promote coalescence and fragmentation of droplets, limiting the emulsifying performance of crude oil. The results of this study provide a better understanding of the formation and fracture process of emulsion under high water cut conditions, offering a theoretical basis for further enhanced oil recovery.