Study on produced water quality variation rule from polymer flooding and mechanism of formation damage

The index of polymer flooding produced water is one of the most pressing issues in oilfield development. Taking LD10-1 oil field in the Bohai Sea for example and taking advantage of the atomic force microscopy, environmental scanning electron microscope and other means of microscopic analysis, the influence of residual polymer on variation of suspended solids concentration and particle size, oil content and the scale-forming ions was studied. The results show that when the residual polymer concentration increased to 150 mg/L, the injection water suspended solids concentration increased by nearly 269.0%, the particle size only increased by 0.3 μm, the filtration rate decreased by 99.3%, the oil content decreased by 86.5% and the scale-forming ions decreased by 18.0%. The residual polymer flocculation and adsorption on the fiber membrane is the main reason which result in the increase of suspended solids and significant decrease of filtration rate, the emulsification making oil content value measured by conventional water quality analysis methods is low, the chelation makes the measurement of the scale-forming ions decreased, and the higher the residual polymer concentration and molecular weight, the more obvious trends of the injection water quality index. In addition, the damage of single residual polymer on a high-permeability reservoir is limited, while the synergy of the suspended solids and oil is the main damage source.