Pore structure and polymer flooding characteristics in the Sa'nan Development Zone of Daqing oilfield

Abstract Accurately predicting polymer flooding performance in the heterogeneous pore systems of mature oilfields remains a critical challenge in enhanced oil recovery. This study addresses this gap by conducting an integrated analysis of pore structure and polymer flooding characteristics specifically for the Sa'nan Development Zone of Daqing oilfield. Through systematic mercury intrusion experiments, casting thin section analysis, and core flooding tests using polymers of varying molecular weights (800–2000 × 10 4 ) and concentrations (500–3200 mg/L), we establish quantitative relationships between pore architecture and displacement efficiency. Results demonstrate that reservoir permeability exhibits a strong positive correlation with equivalent pore radius ( R 2 = 0.89) while showing a powerful inverse relationship with pore throat sorting heterogeneity. Polymer solution viscosity increases non‐linearly with both molecular weight and concentration, with higher molecular weight (MW) polymers providing superior viscosifying efficiency—a 2000 MW polymer achieving 40 mPa · s at 1000 mg/L compared to 18 mPa · s for an 800 MW equivalent. Most significantly, polymer flooding enhances recovery by 15%–25% over water flooding, with higher concentrations yielding greater recovery despite increased injection pressure requirements. The novelty of this work lies in developing predictive models that quantitatively link pore geometry parameters to polymer flooding efficiency, providing a scientific framework for optimizing chemical enhanced oil recovery (EOR) design in heterogeneous reservoirs.