Daqing oilfield is a heterogeneous sandrock oilfield with multilayers. The application of polymer flooding in the field has obtained significantly technological and economic effects. On the bases of numerous lab experiments, it is indicated that polymer solutions of high concentration and molecular weight have better absorption and captation toward the layers than normal solutions do. Besides, the resistance and residual resistance coefficients are much larger. The higher the concentration and molecular weight are, the larger the increment in viscoelasticity is. Once polymer flooding with high concentration and molecular weight is applied, the residual oil saturation will decrease and displacing efficiency will increase. All these lead to higher increment in recovery rate.

Three pilot tests were conducted by means of high concentration and molecular weight. On the bases of the obtained results, industrialized application of the recovery method first began in the N1 block of Sazhong Area in Daqing oilfield in Jan. 2009. In that block, the molecular weight of the polymer solution was 25million Dalton and the concentration was 2000mg/L. Maximum decrement in water cut was 30 percent and enhanced recovery rate was 8.3 %. It was estimated that enhanced recovery rate could ultimately reach 18 percent by the end. The successful application of polymer flooding with high concentration and molecular weight in Daqing oilfield would provide practical experience for the development of similar reservoirs.

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