Expanded Salinity Window of Middle-Phase Microemulsions and Reduced Surfactant Adsorption by Hydrotrope

Using surfactant blends to mobilize residual oil offers a promising technique for enhanced oil recovery (EOR) and surfactant-enhanced aquifer remediation (SEAR). A major financial setback for broader application of this method is the loss of surfactants, as they get absorbed onto reservoir mineral surfaces. This loss becomes even more costly in oil fields with high-salinity formation water. Our research delved into the use of hydrotropes to minimize the surfactant absorption. The impacts of surfactant adsorption with hydrotrope additives were quantified and compared to three representative porous media. Initial tests studied the ideal salinity range influenced by hydrotropes with the observations of Winsor Type III microemulsions with selected surfactants, and four specific hydrocarbons were confirmed through interfacial tension measurements. When tested on three types of porous media, the presence of hydrotropes reduced the adsorption rates: up to 65% on Indiana limestone, 21% on Ottawa sand, and 53% on activated carbon. Notably, our study revealed urea's role in reducing surfactant retention in porous media. This discovery can help modify the salinity range of middle-phase microemulsions, which is crucial for EOR by easing salinity constraints of target reservoirs. The large middle-phase microemulsion window is also very advantageous for other potential applications. Moreover, urea proves to be more effective than typical sacrificial agents for reservoirs, as it binds the surfactant to the liquid rather than acting as a mere sacrificial component. Our research underscores the potential of improving surfactant flooding results by integrating hydrotropes, offering substantial cost savings in surfactant consumption and enhancing the overall efficiency of EOR and SEAR projects.