Changqing old oilfield Jurassic reservoir's average calibration recovery is 24.7%, with geological reserves recovery of 16.6%, water cut of 65.2%. And most of Jurassic reservoirs are in the middle and later field life, part of them has entered the high water cut and high recovery stage. Traditional water flooding way for improving oil recovery becomes more difficult, and new method has to be considered. Maling oilfield BS district is a typical representative, with high water cut of 90.8%, high recovery percent of 26.1% and low oil recovery rate of 0.25%. To explore the new way to improve oil recovery, the polymer and surfactant (SP for short) important pilot test has been developed. The low permeability reservoir indoor core data in high water cut stage and inspection well results indicate that the reservoir permeability, pore combination characteristics and pore type changed greatly after long-term water flooding development. These changes bring more difficulties to the continue development, especially the high injection pressure, which can cause other problems for well pattern infilling and EOR. This paper takes the high injection pressure problem of Maling BS district Jurassic reservoir for example, analyzes the physical property change law on the following aspects: the development mode in the past, core analysis, formation sensitivity, interstitial matter, well test interpretation results, in order to help to further effective development and provide important parameters for tertiary oil recovery technique for similar reservoirs and others.
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