Polymer flooding is a widely used enhanced oil recovery (EOR) method for improving energy efficiency and reducing the carbon footprint of oil production. Optimizing polymer concentration is critical for maximizing recovery while minimizing economic and environmental costs. Here, we present a systematic experimental study which shows that even very low concentrations of polymers yield relatively high recovery rates at adverse mobility ratios (230 cP oil). A series of core flood experiments were conducted on Bentheimer sandstone rock, with polymer concentrations ranging from 40 ppm (1.35 cP) to 600 ppm (10.0 cP). Beyond a mobility ratio threshold, increasing polymer concentration did not significantly enhance recovery. This plateau in performance was attributed to the persistence of viscous fingering and oil crossflow into pre-established water channels. The study suggests that low concentrations of polymer may mobilize oil at high mobility ratios by making use of the pre-established water channels as transport paths for the oil and that the rheology of the polymer enhances this effect. These findings enable reductions in the polymer concentration in fields with adverse mobility ratios, leading to substantial reductions in chemical usage, energy consumption, and environmental impact of the extraction process.

Polymer flooding is a well-established chemical enhanced oil recovery (EOR) method, primarily aimed at improving sweep efficiency. However, the interplay between polymer properties and porous media, particularly the influence on permeability reduction, remains poorly understood. In this study, we investigate how polymer molecular weight, chemistry, and mechanical pre-shearing influence residual resistance factor (RRF) and in situ rheology in Berea sandstone core floods. Post-polymer brine flow exhibits clear non-Darcy behavior, indicating that permeability becomes rate-dependent after polymer adsorption. Application of a Forchheimer-based approach demonstrates that inertial contributions become significant at reservoir-relevant velocities, suggesting enhanced microscopic inertia dissipation associated with interaction between flowing brine and the stationary adsorbed polymer layer. Applying conventional Darcy-based interpretation systematically overestimates RRF under these conditions. RRF increases with polymer molecular weight for polymers with similar bulk viscosities, suggesting that permeability reduction is primarily controlled by effective hydrodynamic size and pore-scale interactions rather than polymer concentration. Mechanical pre-shearing substantially reduces RRF and the non-linear flow contribution, suggesting that laboratory measurements performed on unsheared solutions may overestimate field-scale injectivity impairment. In contrast, an ATBS-containing polymer exhibits relatively low RRF but high apparent viscosity, indicating that alterations in polymer chemistry may override molecular weight as the main factor. The results demonstrate that polymer–surface interactions can induce rate-dependent permeability at reservoir-relevant velocities, and highlight the need for non-Darcy analysis when interpreting polymer core flood experiments for field application.