On the basis of analysis of components and structure of the heavy oil from the 109-1 block in the Dagang oilfield, the high effectiveness viscosity reducer, which can make the mixture of water and heavy oil to become the stable O/W emulsion and decrease viscosity of the heavy oil by above 97% in the case of above 30% water cut and above 1000mg/L dosage of viscosity reducer (for total amount of water and heavy oil), have been developed according to the characteristic of high temperature 80, high mineral salt 20693.75mg/L (especially Ca2+/Mg2+ 805.38 mg/L) and the lower recovery percent of reserves of the 109-1 block heavy oil reservoir in the Dagang oilfield. The viscosity reducer in the produced liquid did not bring unfavorable influence on demulsification. The core displacement experiments show that displacement system containing viscosity reducer can enhance oil recovery by above 22% comparing to water-flooding, and prove that decreasing heavy oil viscosity can improve the oil-water mobility ratio, enhance sweep efficiency and enhance oil recovery.

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