Nano-SiO2-Toughened Polymer Gels for 130 °C Offshore Reservoirs: Gelation Kinetics, Transport Behavior, and Water Shutoff Performance Study

Graphical Nano-SiO₂ (0.02 wt%) extends gel stability to 95 days at 130 °C in seawater (versus 70 days control). SEM-confirmed H-bonding between Nano-SiO₂ silanols and AMPS groups reinforces network. Gelation activation energy (88.2 kJ/mol) derived via Arrhenius model. Nano-SiO₂-toughened polymer gels achieves 34.7 MPa/m breakthrough pressure (10 × base gel) in 1.4 Darcy cores. This study solves water shutoff gel syneresis/ degradation in high-salinity seawater (Ca 2 ⁺+Mg 2 ⁺ >1;500 mg/L) for South China Sea reservoirs. Reservoirs in the western South China Sea have entered a high-water-cut stage, exhibiting significant heterogeneity exacerbated by prolonged water flooding, necessitating urgent profile control measures to enhance oil recovery. Conventional polyacrylamide organic gels fail under the prevailing high-temperature (130 °C) and high-salinity conditions, characterized by divalent cation (Ca 2 ⁺ and Mg 2 ⁺) concentrations of 5650 mg/L. This study developed a robust gel profile control system specifically engineered for such challenging environments. Key parameters including polymer and crosslinker concentrations, gel pH, and temperature were systematically optimized to ensure stability under high temperature and salinity. The optimized formulation demonstrates exceptional stability in seawater at 130 °C, with a gelation activation energy of 88.2 kJ/mol. Incorporating nanosilica significantly enhanced the gel's thermal stability, salinity tolerance, and shear resistance. Scanning electron microscopy (SEM) revealed a strengthened network microstructure. The system exhibits favorable injectivity in 1.4 Darcy permeability cores. Nanosilica reinforcement dramatically increased the gel's breakthrough pressure gradient from 3.45 MPa/m to 34.7 MPa/m. Crucially, the addition of 0.02% nanosilica extended the polyacrylamide gel's functional stability from 70 days to 95 days. This nanosilica-reinforced system offers superior long-term stability and plugging performance, presenting a viable profile control and water-shutoff technology for offshore high-temperature, high-salinity seawater reservoirs.