Construction and Performance Evaluation of Magnetic Nanofluid for Enhancing Conventional Heavy Oil Recovery

To address the high cost of nano viscosity reduction systems, a recyclable magnetic nanofluid (MNF) was constructed. Fe3O4@PEI-C16 was synthesized via coprecipitation and cetyl bromide modification, exhibiting an average particle size of 15.6 nm and saturation magnetization of 50.2 emu/g. Optimized by orthogonal experiments, MNF (0.1 wt % Fe3O4@PEI-C16, 0.3 wt % ODEA, 0.5 wt % JFC-M) showed excellent stability (zeta potential of 30.5 mV at pH = 7), reducing oil–water interfacial tension to 2.23 × 10–2 mN/m and achieving 98.1% viscosity reduction at 53 °C. After 5 cycles, the viscosity reduction rate remained 80.1%. The emulsion dehydration rate was 89.2% at 1 h (97.1% under a magnetic field), accompanied by wettability reversal from 109.2° to 10.6°. Microscopic displacement experiments demonstrated that the mechanism of MNF-enhanced oil recovery primarily involved emulsifying heavy oil, reducing interfacial tension, and altering the wettability. Compared to primary water flooding, MNF flooding, and secondary water flooding, enhanced oil recovery increased by 24.3%. Additionally, the MNF enabled magnetic recovery under an external magnetic field, offering a novel approach to reducing nanomaterial application costs.