Optimization of Polymer Flooding for Enhanced Oil Recovery in Heterogeneous Class II Heavy Oil Reservoirs: Mechanisms and Parameter Optimization

Abstract

Polymer injection has been recognized as an effective method to enhance oil recovery (EOR) in heavy oil reservoirs. However, the impact of different polymer injection volumes and injection strategies on the compatibility and displacement efficiency in heterogeneous reservoirs, particularly in terms of inter-layer and intra-layer heterogeneity, remains insufficiently studied. The lack of understanding of these effects hinders the efficient application of polymer flooding in heavy oil recovery. This study, based on core samples from the D oilfield, investigates the influence of reservoir heterogeneity, polymer injection volume, and injection method on recovery performance through laboratory-scale physical simulation experiments. The results show that, compared to waterflooding, increasing the polymer injection volume from 0.3 PV to 0.9 PV significantly improves the oil displacement efficiency by increasing the amount of polymer entering the low- and medium-permeability reservoirs, adjusting the fluid profile, and facilitating the mobilization of residual oil. The maximum recovery rate was achieved at an injection volume of 0.5 PV. The viscosity reduction injection strategy increased the liquid absorbed in low-permeability layers in heterogeneous inter-layer oil zones, while in intra-layer heterogeneous reservoirs, polymer fingering occurred, leading to increased liquid absorbed in low-permeability reservoirs and pushing some residual oil from high-permeability reservoirs into low-permeability reservoirs, thereby enhancing recovery. This study demonstrates that for heterogeneous Class II heavy oil reservoirs, the optimal polymer injection volume is 0.5 PV, and the viscosity-reducing injection method achieves the best recovery performance by balancing permeability damage and displacement efficiency. These findings provide both theoretical insights and practical guidance for improving polymer flooding performance in heavy oil reservoirs.