Abstract
Traditional polymer flooding for enhanced oil recovery (EOR) suffers from shear instability, poor low-permeability injectivity, and viscosity loss in high-salinity, high-temperature reservoirs. This review critically assesses emerging polymer flooding technologies—including nano-reinforced polymers, hybrid injection techniques, and machine learning-based performance predictions—from 21 publications between 2020 and 2026. Nano-reinforced polymer flooding yields recovery factors (RF) of 44–72% of original oil in place (OOIP), with silica nanoparticles reaching displacement efficiencies up to ~94% and reversing contact angles from ~72° (oil-wet) to ~115° (water-wet). Hybrid injection (polymer-enhanced foam, CO₂-aided surfactant/polymer, and CO₂-cyclic solvent injection) achieves maximum recoveries of 70–97% OOIP via combined mobility reduction and ultra-low interfacial tension (10^{-3} mN/m). Capsule polymer flooding demonstrates delayed thickening (resistance factors increasing from 2 to 25–32), making it ideal for high water cut and offshore wells. Critical performance factors include optimal nanoparticle concentration (0.25–0.5 wt%), type and shape (SiO₂ > Al₂O₃/TiO₂; fibrous > spherical), salinity/temperature tolerance, and reservoir heterogeneity. Key challenges include nanoparticle agglomeration/retention, high synthesis costs, gas channeling, and limited understanding of long-term reservoir impact and scalability. Next-generation systems will feature smart responsive polymers, sustainable nano-enhancers, real-time digital twins with adaptive control, and reservoir-specific customization protocols.