Preparation and performance evaluation of amphiphilic Janus SiO2 nanofluids for enhanced oil recovery in low-permeability reservoirs

• A novel Janus nanofluid was designed for low-permeability oil reservoirs. • Janus nanoparticles were characterized for EOR performance and stability. • The nanofluid shows strong interfacial activity at ultra-low concentrations. • 0.02 wt% Janus fluid achieves 16.9% oil recovery with excellent stability. To meet the requirements of tertiary oil recovery in low-permeability, tight reservoirs, this study synthesized silica-based amphiphilic Janus nanoparticles. The organic hydrophobic groups were grafted onto the surface of silica nanoparticles via in situ generation and chemical fracture methods. The chemical structure of the synthesized Janus nanoparticles was characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FT-IR). Their interfacial properties were systematically investigated through measurements of interfacial tension, contact angle, and emulsification performance. The results indicate that when the concentration of Janus nanoparticles reaches or exceeds 0.02 wt%, the interfacial tension between the amphiphilic nanoparticle dispersion and crude oil remains on the order of 10 -2 mN/m, demonstrating excellent interfacial activity. Additionally, the Janus nanofluid effectively alters rock wettability, converting it from oil-wet to water-wet. Janus-SiO₂ nanoparticles constructed with trimethylsilane as the hydrophobic carbon chain and hydroxyl groups as the hydrophilic end groups exhibit uniform particle size distribution and excellent dispersion stability in mineralized water. Core-scale displacement experiments with low-permeability sandstone indicate that the amphiphilic nanoparticle dispersion at a concentration of 0.02 wt% can further enhance oil recovery by 16.9% compared to water flooding alone. The mechanisms by which amphiphilic nanoparticles improve oil recovery in low-permeability tight reservoirs mainly include reducing oil–water interfacial tension, altering rock wettability, promoting in situ emulsification, and strengthening the interfacial film, thus demonstrating promising application prospects for the development of low-permeability tight reservoirs.