Abstract

During polymer flooding, the behaviors of water injection profile reflect the flooding efficiency and its performance in medium and low permeable layers represents the sweep efficiency of the reservoir. In this work, the polymer flooding wells in Bohai Oilfield is analyzed and the observations on the performance are, with more polymer injected, the injection profile is characterized by: In most of the wells, vertically, the intake profile of each layers is improved efficiently and water absorption of low and medium permeable layers increase correspondingly; however, in some wells, the injection profile is not improved vertically but the water absorption of high permeable layers increases instead while low and medium permeable layers do not absorb any water; in addition, water absorption volume in high permeable layer is higher than that of the total volume of low and medium permeable layers, which is prejudicious for polymer flooding. By analyzing the field scale data, it is found that the differential of formation capacity between layers has big impact on water injection profile improvement by polymer flooding. Nevertheless, with certain formation capacity, injection profile of low and medium permeable layer, with the increase of injection volume, will increase first, then decrease and then increase again. Based on the study, it should be avoided to inject polymer to wells whose formation capacity differential is large. If it is ineluctable, injection profile should be adjusted before injecting polymer. For those wells whose intake profile is improved obviously, attention should be paid on the rules of the injection profile with the increase of injected polymer, and conduct zonal polymer injection, injection profile adjustment or increase polymer volume to enhance polymer flooding effect when its relative water absorption volume reduce.

Key word: Polymer flooding, offshore oil field, water injection profile, influences factors.