Smart “Switchable Wettability” Magnetic Nanoparticles: Fe ₃ O ₄ @SiO ₂ –P/O for Temperature-Controlled Selective Water Shutoff

To address water channeling in late-stage oilfields and overcome the limitations of conventional polymeric water plugging agents, this study developed an innovative magnetic-temperature dual-responsive Fe3O4@SiO2–P/O Pickering emulsion (FSP). This water plugging agent was developed using core–shell Fe3O4@SiO2 nanoparticles. After grafting modification with polyethylene glycol 200 (PEG200) and n-octyltriethoxysilane (OTES), the resulting nanoemulsifier (Fe3O4@SiO2–P/O) exhibits hydrophilic–hydrophobic transition properties at 90 °C. The FSP water plugging agent was successfully prepared using these nanoparticles as an emulsifier. Experiments show the FSP emulsion is stable at room temperature but demulsifies rapidly above 90 °C. It can also be precisely separated with a magnetic field. Core displacement experiment demonstrated its excellent selective plugging ability, achieving a 94.34% water plugging rate and only an 18.8% oil plugging rate. Injectability experiments also demonstrated its deep migration capability. This research achieves temperature control over the plugging material’s hydrophilicity/hydrophobicity by manipulating the conformational changes of the surface polymers on the Fe3O4 nanoparticles at high temperatures, while utilizing its magnetic properties to achieve precise control over its mobility.