Self-healing movable gel for enhanced heavy oil recovery in harsh fractured reservoirs

Fractured heavy oil reservoirs are characterized by deep burial depth and complex fracture networks, leading to significant heat loss during thermal recovery processes. However, the existing cold production oil-flooding agent has insufficient performance and low viscosity retention rate in high-temperature and high-salinity environments. Based on the strong hydrogen bonding of hydroxylamine organic compounds, a N-methylglucamine functionalized movable oil-flooding gel (N-MG@MFG) is synthesized via a one-pot method for improving fluidity, temperature tolerance, and salt resistance in heavy oil reservoir. N-MG@MFG with various viscosity (ranged from 221 to 854 mPa s) was successfully prepared by using ternary copolymers P(AM/ACMO/AMPS) as gel skeleton, phenolic resin as a cross-linking system and N-methylglucamine as a functional modifier. This novel gel exhibits unprecedented stability, retaining a high viscosity exceeding 200 mPa·s at 150 °C and 22 × 104mg/l salinity, outperforming current agents by a significant margin. By fitting the Arrhenius equation, it is revealed that N-MG@MFG can retain its original molecular structure under extreme conditions. Notably, its resistance to dilution and shear force is groundbreaking: the viscosity retention rate remains above 69.8% after 85% dilution and surpasses 86.3% post three shear cycles, showcasing remarkable self-healing capabilities. Cryo-scanning electron microscopy, proton nuclear magnetic resonance, and x-ray photoelectron spectroscopy reveal a unique mechanism where N-methylglucamine, via hydrogen bonding, modulates polymer cross-linking density to endow fluidity, a feature absent in traditional gels. In oil flooding experiments, N-MG@MFG achieves a remarkable 75% oil recovery rate in pure gel flooding and 71% in slug flooding of fractured cores, representing a significant leap in efficiency. This study not only fills the gap in developing high-performance oil flooding agents for extreme reservoir conditions but also offers an innovative molecular design concept, opening up new avenues for heavy oil reservoir exploitation.