The oil/water interfacial behavior of microgels used for enhancing oil recovery: A comparative study on microgel powder and microgel emulsion

Microscale crosslinked polymeric hydrogels, termed microgels, have attracted considerable attention as enhancing oil recovery (EOR) agents due to their favorable in-depth fluid diversion effect. However, the oil/water interfacial behavior of microgels remains unclear, limiting the comprehensive understanding of the EOR mechanism. In this study, the oil/water interfacial behavior of microgel powder (MP) and microgel emulsion (ME) was studied through emulsification tests and interfacial tension (IFT) measurements. Despite the similar properties of the microgel particles, such as morphology, size distribution and zeta potential, ME exhibited better emulsification performance than MP in deionized (DI) water due to the presence of additional surfactants in ME. However, since the competitive adsorption between the microgel particles and surfactants on the oil/water interface changed with salinity, ME exhibited a higher emulsion volume but lower emulsion stability than MP in brine. Moreover, W/O and O/W emulsions were formed in DI water, but only an O/W emulsion was formed in brine for ME. Furthermore, MP exhibited better IFT reduction performance in brine due to the weaker steric hindrance and tighter adsorption layer on the oil/water interface. In contrast, ME showed better IFT reduction performance in DI water owing to the interaction between the microgel particles and the surfactants. Considering that MP is usually used in the laboratory while commercial microgels are provided in the form of ME, the different oil/water interfacial behaviors of MP and ME may result in an inconsistent understanding of the EOR mechanism in laboratory study and field application.