Synergistic stabilization of emulsions by microspheres and surfactants for enhanced oil recovery

During oil displacement, surfactants often encounter challenges such as emulsion instability and channeling, which can compromise their efficiency. To address these issues, polymer microspheres were synthesized via reverse microemulsion polymerization using acrylamide, 2-methyl-2-acrylamidopropane sulfonic acid, and stearyl methacrylate as monomers, with N,N-methyl-enebisacrylamide as the crosslinker. The microspheres were then combined with sodium alkyl alcohol polyoxyethylene ether carboxylate to enhance emulsion stability and expand the swept volume of surfactant. A stable reverse microemulsion system was prepared using the maximum water solubilization rate as the indicator, and microspheres were synthesized based on this system. The ability of the microspheres to enhance emulsion stability was systematically evaluated. The plugging performance and enhanced oil recovery (EOR) efficiency of the microsphere/surfactant composite system were assessed through core seepage and oil displacement experiments. The experimental results demonstrated that microspheres were successfully prepared in a water-in-oil reverse microemulsion system with a solubilization rate of 42%. The emulsion stability was evaluated under an oil-to-water ratio of 7:3, a temperature of 80 °C, and a salinity of 44,592 mg/L, by manually shaking the test tube five times. It was observed that the complete phase separation time of the emulsion increased from 10 to 120 min after the addition of microspheres. Under different permeability conditions (100 × 10⁻³, 300 × 10⁻³, 500 × 10⁻³ μm²), the recovery efficiency of the composite system increased by 4.5%, 8.3%, and 4.8%, respectively, compared to a single surfactant system. The microspheres developed in this study enhanced emulsion stability and increased the swept volume of surfactant within the formation, significantly boosting its oil recovery efficiency.