Optimizing the injection parameters of polymer flooding based on the change laws of water cut

At present, the methods specifically researching adjustment measures and parameter optimization of polymer flooding rarely study the single-well polymer flooding effect and there are no available technologies and experience as reference. The water cut curve of polymer flooding was divided into four stages, including non-response stage, water-cut decline stage, continuous response stage and water-cut return stage. In the meantime, water-cut laws were quantitatively characterized by using three parameters, e.g. response time, water-cut decline amplitude and effective response stage. Then, main control factors in different water-cut stages were determined by means of comprehensive numerical simulation and mathematical statistics, and the mathematical model of the parameters for quantitatively characterizing main control factors and water cut was established on the basis of multi-variant regression method. Finally, the optimized decision making model for the polymer injection parameters of different water-cut stages was established. And it is indicated that in the non-response stage, balanced injection-production measures shall be taken with the construction of resistance coefficient as the core. In the water-cut decline stage, effect induction and promotion measures shall be taken with the increase of injection rate as the core. In the continuous response stage and the water-cut return stage, differential injection shall be implemented with the change of polymer concentration as the core. In SZ Oilfield of Bohai Sea, one strategy for one well is conducted based on the water-cut stage of each well. In 2019, polymer flooding parameter optimization was carried out ten well times, which provides the cumulative oil increment of 2.4×10⁴ m³.