# Comparative Evaluation of Polymer Screening and Oil Displacement Performance in Class III Reservoirs of the Daqing Oilfield

## TL;DR

This study evaluates polymer solutions for improving oil recovery in low-permeability, heterogeneous reservoirs in the Daqing Oilfield.

## Contribution

The study identifies optimal polymer formulations for Class III reservoirs based on experimental screening and displacement performance.

## Key findings

- A 1500 mg L−1 polymer solution with Mw of 16 × 106 Da achieved 53.38% ultimate recovery in Class III reservoirs.
- The same polymer solution showed higher displacement and sweep efficiencies in high- and low-permeability layers compared to a 1200 mg L−1 solution with Mw of 19 × 106 Da.

## Abstract

Class III reservoirs in the Daqing Oilfield are characterized by low permeability and strong heterogeneity, posing significant challenges to enhanced oil recovery (EOR). To improve the recovery efficiency of these reservoirs, the viscosifying ability, stability, shear resistance, and profile-control performance of fifteen polymer solutions were experimentally evaluated, and the two most compatible formulations were selected for the Daqing Class III reservoirs. Subsequently, a three-dimensional physical model equipped with real-time saturation monitoring was employed to compare the EOR performance of the selected polymers. The results indicate that a 1500 mg L−1 polymer solution with a molecular weight (Mw) of 16 × 106 Da and a 1200 mg L−1 polymer solution with an Mw of 19 × 106 Da exhibit the best compatibility with the target formation. After injecting the 1500 mg L−1 (Mw = 16 × 106 Da) polymer solution, the ultimate recovery reached 53.38%, with displacement efficiencies of 64.34% and 58.16% and sweep efficiencies of 92.26% and 80.35% in the high- and low-permeability layers, respectively. Injection of the 1200 mg L−1 (Mw = 19 × 106 Da) polymer solution yielded an overall recovery of 47.71%, corresponding to displacement efficiencies of 60.34% and 54.16% and sweep efficiencies of 88.52% and 76.38%. Consequently, the 1500 mg L−1 (Mw = 16 × 106 Da) polymer solution delivers the highest recovery increment in Class III reservoirs. These findings provide valuable guidance for the efficient polymer-flooding development of Class III reservoirs in Daqing and analogous formations worldwide.