Study On Sequence Stratigraphy And Depositional Systems Of Yaojia Formation-Nenjiang1 Member In Daqing Placanticline

Songliao Basin is the biggest non-marine oil and gas bearing basin in the world. Daqing Oilfield which is located in Daqing Placanticline has been regarded as the first oilfield in China for nearly sixty years for its hydrocarbon output and played an important role in national economy development.Because of its strategic role, scale and depositional environment, Songliao Basin has been the hot point of research on sequence stratigraphy and sedimentology for a long period of time. But there are still some fields need improved, such as studies on palaeotectonics and palaeoclimate background in which the palaolake developed in Cretaceous Period and genesis and controlling factors of high frequency depositional cycle or sequence.Therefore, the research in sequence stratigraphic framework, controlling factors on depositional systems and sequence including palaeotectonics, palaeoclimate, palaeogeomorphology, lake level changes and provenance, and identifying sand bodies’ distribution within high resolution sequence stratigraphic framework by using seismic sedimentology method has great significance both theoretically and practically.On the theoretical basis of sequence stratigraphy, the analysis of sequence was made in Daqing Placanticline by using 3-D seismic, log, core, welwitschiopsida, isotope and geochemistry data. Yaojia Formation and Nenjiangl Member can be divided into three third-order sequences and several fourth-order, fifth-order sequences. Different types of sequence boundary and stratigraphy character were gained.By using seismic sedimentology method within the established isochronous stratigraphic framework, the main depositional systems such as meandering river shallow-water delta in Yaojia Formation and lake-turbidite deposit in Nenjiangl Member have been identified. The characters of depositional system distribution and evolution were studied.The study concluded that it was palaeoclimate, deposit sources and lake level changes rather than palaeotectonics that had controlled development and evolution of depositional systems and sequence stratigraphy in the depression stage.Through analysis of reservoir forming conditions, a conclusion can be obtained that Daqing Placanticline had good reasons to form potential structural traps, lithologic traps and structural-lithologic complex traps. And target strata had superior reservoir forming conditions. Delta front in Yaojia Formation and lake turbidite in Nenjiangl Member are favorable reservoir facies belts. Lithostratigraphic and structural-lithologic traps related with small amplitude structure should be paid moreattention to in the future.