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To further enhance oil recovery in reservoir after chemical flooding, an efficient activator formulation for promoting metabolism of endogenous microorganism was researched. Changes in community structure, growth and metabolites of endogenous microorganism were analyzed by methods of aerogenic experiments, physical simulation experiments, electron microscopy scanning (SEM), T-RFLP and Pyrophosphate sequencing. To evaluate whether endogenous microorganism activator screened in laboratory could activate endogenous microorganisms and enhance oil recovery in reservoirs after polymer flooding. The flooding effect and mechanism were studied, and this activator was used in a testing well group in Daqing oilfield. The results of the aerogenic experiments showed that the activator could activate the endogenous microorganisms in the injected water and make them produce a lot of biogas. The pressurized gas reached 2MPa after 60d static culture of activator in a high pressure vessel. The results showed that the activator could activate the endogenous microorganisms in the injected sewage and make them have a lot of growth and reproduction in the core and physical simulation of natural core flooding experiment. In the field test,the incremental oil production was 5957 t while the water content declined by 2.2% after injecting the activator, which provides an effective way to further enhance oil recovery in reservoir after chemical flooding.

Laboratory evaluation showed that rhamnolipid combined displacement system with low and wide effective concentration (0.125%~1.0%) can reduce interfacial tension with Pubei oil and water to 10-2mN/m. Injection of 0.5PV of rhamnolipid combined displacement system in natural core simulating reservoir permeability can increase recovery by 7.9%~9.3% more than water flooding. Field test for rhamnolipid combined displacement system was carried out with 2 injectors and 9 producers. Alternating injection is performed with two slugs with total volume of 19895.5m3, containing 250.9t of dosage. During 13 months of field test, stageous cumulative incremental oil production was 2014t, with 224t of average single well incremental oil. Daily oil production increased from 1.5t/d to 1.85t/d, average water cut decreased by1.5%, and input-output ratio was 1:2.4. This study provided a new way to improve oil recovery for other similar water flooded reservoirs.