Characteristics of Preferential Flow Paths in Reservoirs After Polymer Flooding and an Adaptive Compound Flooding Method

When a reservoir is subjected to long-term water and polymer flooding, the formed preferential flow paths are widely distributed in the formation, and the displacing fluid effect is reduced, thus leaving a large amount of remaining oil unexploited. To enhance the oil recovery efficiency after polymer flooding, it is important to provide effective methods to block the preferential flow paths. The statistical data analysis results of 20 wells after polymer flooding in the Daqing oilfield show that the remaining oil and the preferential flow paths are mainly distributed vertically in the sedimentation units named PI2 and PI3, and the physical plugging and traditional adjusting techniques are not effective. Considering the above, an adaptive compound flooding method is put forward, which is based on the idea of “plugging, adjusting, and flooding. Laboratory experiment results show that the enhanced oil recovery (EOR) of the new polymer flooding method is 13.6%, which is 4.9% higher than that of alkaline/surfactant/polymer (ASP) flooding. The polymer consumption of the new method is more than 10% lower than that of conventional polymer flooding.