Performance of Imbibition Oil Recovery Enhanced by a Novel Chemically Modified SiO ₂ Nanofluid for Low-Permeability Reservoirs

Surfactant-based nanofluids have been proven to be promising for chemical-enhanced oil recovery (CEOR) owing to their effects on wetting reversal and interfacial tension (IFT) reduction. In this study, the surfaces of SiO₂ nanoparticles (SNPs) were coated with (3-aminopropyl) triethoxysilane (APTES) to create amino groups that combined with the sulfonic group of the zwitterionic surfactant cocamidopropyl hydroxysultaine (CAPHS) through ionic bonds to yield CAPHS-APTES-SNPs. High-resolution camera observations and particle size and zeta (ζ)-potential analyses indicated that APTES-SNP fluid and CAPHS-APTES-SNP fluid could exhibit better thermal stability and salt resistance than SNP fluid. The obtained nanofluid exhibited excellent thermal stability and salt tolerance under 50 °C and 50,000 ppm brine conditions. CAPHS-APTES-SNPs effectively reduced the IFT between oil and water from 16.08 to 2.02 mN/m and changed the contact angle of oil-wet rock surfaces from 135.8 to 45.2° (38.4° for APTES-SNPs), demonstrating significant wettability reversal. Compared with APTES-SNPs, CAPHS-APTES-SNPs showed 92% higher long-term stability and achieved a maximum imbibition oil recovery of 27.43%. The improved recovery was attributed to the synergistic effects of enhanced surface stability, moderate IFT, and strong water-wet transition induced by structural disjoining pressure. This work provides a promising strategy for developing high-performance, salt-tolerant nanofluids for enhanced oil recovery in low-permeability reservoirs.