Optimization of Polymer-Flooding Parameters and Front Propagation Behavior in the Central-Western Block I of the Lanan District.

To clarify the propagation behavior of the polymer-flooding front in highly heterogeneous, high-water-cut reservoirs, polymer-system screening, plugging-performance evaluation, and one-dimensional and three-dimensional saturation-monitoring displacement experiments were conducted for the central-western Block I of the Lanan District. The results showed that both HPAM-1 and HPAM-2 exhibited good viscosity-enhancing performance and injectability. The 2,000 mg/L HPAM-2 system exhibited the best plugging performance in the high-permeability layer, with a plugging rate of 80.5%, effectively mitigating uneven interlayer flow distribution. One-dimensional experiments showed that polymer flooding improved the utilization of the low-permeability layer and reduced interlayer differences in front propagation. Compared with the 1,800 mg/L HPAM-2 system, the 2,000 mg/L HPAM-2 system delayed front breakthrough in the high-permeability layer from 0.8 PV to 1.0 PV and achieved an incremental recovery factor of 20.82%, with a combined recovery factor of 65.91%. Three-dimensional experiments showed that the polymer-flooding front still preferentially advanced through high-permeability regions, while the oil saturation in low-permeability regions was further reduced, thereby improving areal sweep efficiency. The incremental recovery factor during polymer flooding reached 14.14%, and the final recovery factor reached 57.75%. These findings provide an experimental basis for optimizing polymer-flooding parameters in similar highly heterogeneous, high-water-cut reservoirs.