Nonlinear Seepage Characteristics and Microscopic Oil Displacement Visualization Experiment of Highly Viscoelastic Polymer

Understanding the nonlinear seepage behavior and microscopic displacement mechanisms of highly viscoelastic polymers is essential for optimizing polymer flooding in heterogeneous reservoirs. This study is aimed at clarifying how polymer viscosity, elasticity, and pore‐scale deformation jointly influence flow resistance and oil displacement performance. Two polymer systems—a conventional HPAM and a highly viscoelastic polymer—were selected as research objects. A series of rheological measurements, nonlinear seepage experiments using sand‐pack models, and microscopic visualization tests were conducted to quantify the effects of polymer concentration, elastic modulus, permeability, and back pressure on injection resistance and sweep behavior. The results demonstrate that, at the same concentration, the highly viscoelastic polymer exhibits substantially higher viscosity and elastic modulus than conventional HPAM, with elasticity increasing sharply above 0.20 wt%. Under matched apparent viscosity, the highly viscoelastic polymer shows consistently higher flow resistance due to elastic energy storage and release during repeated contraction–expansion through pore throats. Apparent viscosity increases with permeability and exhibits opposite trends with back pressure at low and high shear conditions. Microscopic visualization reveals that higher polymer concentration and stronger elasticity improve sweep efficiency, suppress viscous fingering, and reduce residual oil. At 2.0 PV injection, the sweep efficiency of the 0.25 wt% highly viscoelastic polymer reaches 85%, significantly exceeding that of conventional polymer. This work provides new quantitative evidence linking polymer elasticity to both nonlinear seepage characteristics and pore‐scale displacement behavior. The findings enhance the understanding of viscoelastic polymer flooding mechanisms and offer guidance for designing polymer systems with improved sweep and displacement efficiency in heterogeneous reservoirs.