Experimental study of imbibition depth and oil migration mechanism of a magnetic nanofluid for low-permeability reservoir oil recovery improvement

Nanofluids are considered promising agents for enhanced oil recovery in low-permeability reservoirs, but their application is often restricted by poor thermal and saline resistance and high costs. Moreover, limited studies have addressed the imbibition depth and oil migration processes during nanofluid imbibition in low-permeability reservoirs. In this work, a magnetic core–shell structured nanoparticle Fe₃O₄–TiO₂ was synthesized using inexpensive Fe₃O₄ nanoparticles and tetrabutyl titanate. The synthesized nanoparticles exhibited excellent thermal and saline resistance as well as recyclability. Their structure and functional properties were characterized. The nuclear magnetic resonance technology was applied to investigate the imbibition depth and the oil migration process during magnetic nanofluid imbibition. Results showed that the magnetic nanofluid possessed interfacial activity, wettability alteration capability, and strong thermal and saline resistance. At 80 ℃, the imbibition recovery of magnetic nanofluid reached 32.19%, 3.59% higher than that of SiO₂ nanofluid. The recycle rate of magnetic nanofluid was 81.31%, effectively reducing operational costs. The final imbibition depth of magnetic nanofluid reached 18.82 mm, with an average imbibition rate of 3.14 mm/d, which is 21.97% higher than that of the SiO₂ nanofluid and 39.10% higher than that of the simulated formation water. The imbibition process of magnetic nanofluid was dominated by capillary forces, with oil in micropores displaced into macropores. We expect that this study can contribute to the effective development of low-permeability reservoirs and provide theoretical guidance for field applications.