Multifunctional nanofluids for enhanced oil recovery by simultaneous in situ mobility control and displacement efficiency improvement

Compared with conventional chemical enhanced oil recovery methods, micro/nanofluid-based emulsion systems offer several advantages, including improved mobility control, enhanced stability, and effective modification of interfacial properties, while requiring lower chemical dosage and exhibiting better tolerance to harsh reservoir conditions. This study systematically evaluated the potential of a novel nanofluid-based emulsion as an enhanced oil recovery agent, with emphasis on its rheological behavior, emulsion stability, and interfacial performance. Rheological measurements demonstrate that emulsion viscosity is strongly influenced by the water-to-oil ratio and mixing duration. Systems with low oil content exhibit only modest viscosity changes, whereas increasing oil fraction and mixing time result in pronounced viscosity enhancement, indicating the formation of structured emulsion networks. This viscosity growth contributes to improved emulsion stability, which is further supported by microscopic observations revealing complex multiphase structures. Interfacial characterization shows that the nanofluid-based emulsion effectively lowers the oil-water interfacial tension and induces a strong wettability shift toward water-wet conditions, both of which are favorable for enhanced oil displacement. Microfluidic displacement experiments provide pore-scale evidence that the combined effects of viscosity enhancement, improved emulsion stability, interfacial tension reduction, and wettability alteration lead to efficient mobilization of residual oil. Visual observations confirm in situ emulsion formation within the porous network and improved sweep behavior compared with conventional water injection. Overall, the results highlight the multifunctional role of nanofluid-based emulsions in stabilizing flow, enhancing sweep efficiency, and modifying interfacial dynamics, demonstrating their strong potential as an advanced chemical strategy for enhanced oil recovery applications.