Polymer flooding, as the most effective chemical EOR technique, was widely and used in onshore oilfields in the world. Also, it has been successfully applied in China offshore oilfields as a major EOR technology. In general, compared with water flooding, the production rate in polymer flooding drops by less than 30% according to observations of onshore field application. However, the production rate dropped much more severely in mid to late stage of polymer flooding for plugging problems in W offshore oilfield, which is over 50% in some producers and leads to poor flooding performance and less incremental oil. In this study, we perform a systematic analysis through integrating production dynamic analysis, well testing and reservoir simulation for the mechanisms and impacts of the plugging during the polymer flooding based on actual field data. First, a typical 1-injector & 1 producer polymer flooding reservoir model was established. Through simulation with the detailed description of reservoir and polymer properties, the impacts of key parameters affecting the production rate of producers in different stages of polymer flooding were analyzed. In addition, the dynamic characteristics of well performance under the condition of different plugging location were examined. After that, the local grid radial refinement technology was utilized to calculate the plugging degree and pollution radius of the target wells. Finally, a full-field corner grid system numerical model with local grid radial refinement near the wellbore was built in W fileld. We performed history matching with target injectors and producers and determined the plugging degree of pollution radius near above wells. Through this field case study, the relationship between production rates and different stages of polymer flooding was identified. In addition, a diagnostic plot for characterizing the impact of plugging location on dynamic well performance was generated. Furthermore, the degree of plugging and pollution radius of all target wells was determined accurately. This study provides critical insights for understanding the polymer plugging mechanism and its effect on polymer flooding effectiveness in the offshore oil field. It also delivers a good reference for plugging removal design and optimization of polymer flooding strategy to maximize oil recovery.
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