Daqing Oilfield is one of the earliest which develop displacement technology by polyacrylamide (PAM). 1 ton polymer can increase 100 to 120 tons of oil, the recovery from above 40% to nowadays 50%. In view of the geological and physicochemical characteristics, a series of technologies have been developed, such as polymer flooding mechanism, the productivity forecasting, proposal optimization, domestic excellent quality polymer production, surface injection, downhole separate layer injection, and separate layer testing during injection, etc.. The oilfield is characterized by heterogeneous multi- layer sandstone reservoir, during polymer flooding, separate layer injection technology is also needed to alleviate the interlayer differences, enhance oil recovery and improve the whole development effect.

After polymer flooding in main oil layers, the object of polymer flooding in Daqing Oilfield turned to laminated layers with lower permeability and more interlayer differences, these layers were compatible to polymer solution with medium or low molecular weight, using polymer solution with the same molecular weight for displacement will cause difficult injection into these poor layers, and thus have an impact on polymer flooding effect. In order to solve this problem, a new technology is developed through injection of polymer solution with different pressure and different molecular weight in different layers, which can realize the adjustments of both separate layer polymer molecular weight and injection rate, and also field test was carried out in the polymer injection blocks, good results of well stimulation have been seen.

This paper briefly introduces the development and practice of separate layer polymer injection technologies, presents its focus on the principle, string structure and parameters of eccentric different molecular weights polymer injection technology and its field applications in Daqing oilfield.

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