The reservoirs with low permeability in the western part of Block Ⅲ of District Ⅰ to District Ⅲ in Xingshugang Oilfield in Daqing Oilfield experienced various development stages,such as natural energy,water flooding,and polymer flooding,leaving a complex distribution of residual oil and a pressing need to improve development efficiency.Therefore,Block Ⅲ was divided into three regions featured by:normal polymer flooding,casing-damaged polymer flooding,and polymer follow-up water flooding based on the study of residual oil and analysis results of development effectiveness,so as to develop proper technical strategies for improving development effectiveness with artificial core displacement and numerical simulation techniques.After years of chemical flooding,residual oil in the normal polymer flooding region is sporadically distributed at the edges of sand bodies and areas with low permeability.In the casing-damaged polymer flooding region,the producing performance of oil layers is poor due to casing damage,and the remaining oil reserves there is high.Based on the conditions described above,optimization is carried out in three aspects:development method,oil displacement system,and well pattern design with the full consideration of different regional characteristics.For normal polymer flooding regions and polymer subsequent water flooding regions,a five-spot well pattern dilution of regular polymer flooding was adopted with a well spacing of 175 meters and a plug size of 0.40 times of the pore volume.While for casing-damaged polymer flooding region,a local infilled five-spot well pattern of regular polymer flooding is applied with a well spacing of 140 meters and a plug size of 0.70 times of the pore volume.An increase of 3.53 percentage points is predicted in recovery rate.After the implementation of these measures,the cumulative injection of polymer pre-plugs in Block Ⅲ is estimated to be 0.10 times the pore volume,an expected oil increase of 9 780 tons.This study can provide reference for improving development efficiency in polymer flooding blocks.
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