Magnetic Responsive Pickering Emulsion Containing SiO₂–Fe₃O₄ Particles with Highly Selective Water Plugging in High-Salt Reservoirs

The development of selective water-plugging materials is a challenging task in oil field research. A magnetically responsive emulsion containing SiO₂-Fe₃O₄ particles was prepared using the mechanical emulsification method. The stability, magnetic demulsification, and water-plugging performance of the emulsion were evaluated. The results showed that the emulsion with SiO₂-Fe₃O₄ particles could maintain stability for up to 30 days at room temperature. However, when the temperature exceeded 80 °C, the thermal stability decreased with an increase in the SiO₂-Fe₃O₄ ratio. Meanwhile, based on the magnetic response of Fe₃O₄ particles, the demulsification behavior of the emulsion under a constant magnetic field strength was analyzed, revealing that the stability of the emulsion is jointly determined by the particle membrane and surfactant. Results from the displacement experiments showed that when the water phase plugging rate reached more than 97%, the oil phase plugging rate was only 45%. Mechanism analysis and contact angle characterization verified that the plugging rates for the water and oil phases depend on the cross-linking form of the SiO₂-Fe₃O₄ composite material. Fe₃O₄ particles "wrapping" around SiO₂ particles are beneficial for enhancing water-plugging performance.