Abstract
Polymer flooding is widely implemented as a mobility-control method for enhanced oil recovery (EOR); however, incremental recovery beyond mobility improvement is frequently reported and remains incompletely explained. This review examines the role of viscoelasticity in improving micropore sweep efficiency during polymer flooding. A clear distinction is made between micropore access (flow penetration into low-connectivity microdomains) and micropore mobilization (release of trapped oil in dead-end pores and corners). The analysis synthesizes experimental observations, pore-scale simulations, and rheological considerations to evaluate whether elastic stresses contribute to additional oil displacement mechanisms beyond shear viscosity effects. Particular attention is given to extensional flow behavior in converging–diverging pore geometries, the influence of crude oil viscosity, and the role of salinity, temperature, and mechanical degradation in suppressing viscoelastic responses. The review demonstrates that viscoelastic contributions to oil recovery are condition-dependent and most pronounced within specific viscosity and operational windows. Variability in reported results is largely attributed to inconsistent rheological characterization and insufficient consideration of degradation effects. Standardized brine-conditioned rheological protocols, including extensional metrics where feasible, are recommended to improve reproducibility and predictive capability. The findings highlight the need for multi-scale validation linking pore-scale mechanisms to core-scale displacement and field performance.