Practice and Understanding of Separate-Layer Polymer Injection in Daqing Oil Field

Summary Daqing oil field is one of the earliest to develop displacement technology by polyacrylamide (HPAM). One tonne of polymer can increase 100 to 120 tonnes of oil; the recovery increases from 40% (OOIP) to 50% (OOIP). In view of the geological and physicochemical characteristics, a series of technologies have been developed, such as polymer-flooding mechanism, productivity forecasting, proposal optimization, domestic excellent-quality polymer production, surface injection, downhole separate-layer injection, and separate-layer testing during injection. The oil field is characterized as a heterogeneous multilayer sandstone reservoir. During polymer flooding, separate-layer injection technology is also needed to mitigate the interlayer differences, enhance oil recovery, and improve the whole development effect. After polymer flooding in main oil layers, polymer flooding in Daqing oil field turned to lower-permeability layers. To obtain a better displacement effect, the injected-polymer molecular weight is usually determined according to the injectivity of high-permeability layers. However, if polymer solution with the same molecular weight is injected in each layer, it will cause blockage in low-permeability layers. In order to solve this problem, a new technology is developed that can control both separate-layer polymer molecular weight and injection rate; the injection profile was improved greatly in later field applications. This paper introduces the development and practice of separate-layer polymer-injection technologies, and presents the principle, string structure, and parameters of eccentric different-molecular-weight polymer-injection technology and its field applications in Daqing oil field.