Paleogeographic Background and Sedimentary Facies Study on the Lower of the Third Member of the Shahejie Formation of Paleogene in Dongpu Sag

　　Paleogeographic Background and Sedimentary Facies Study on the Lower of the Third Member of the Shahejie Formation of Paleogene in Dongpu Sag
　　Dongpu sag is a typical salt lacustrine sub-basin with prolific oil and gas in Bohaiwan basin in east China. For a long time, main type of subtle reservoir, especially the lithologic, distribution law and exploration method are not recognized clearly. Therefore, investigating the sedimentary facies, the spreading characteristic of facies zone and the relations of them to the oil layer disposition, the sandstone body type and the space-time distribution rule are very important to the oil field of Dongpu sag for further exploration and the development.According to observing and describing core of 22 wells in the region, 9 kinds of original structure, 4 kinds of deformational structure, Block neodymium magnet pyrite and fish fossil are identified, and 4 major kinds (gravel stone, sandstone, siltstone and mudstone) lithofacies are divided.
　　On the base of core observation, combining well logging and logging, 9 sorts of log facies and the association are divided.Based on the principle of high resolution sequence stratigraphy, as well taken into account synthetically base level cycle and volumetric partitioning and facies differentiation controlled by tectonics movement and sediment supply and sea-level change and climate, high resolution sequence stratigraphy division was applied in the lower of the third member of the Shahejie Formation. The lower of the third member of the Shahejie Formation can be divided into 1 long-term cycle and 2 mid-term cycles.On the basis of lots of forerunners’ data and research in this thesis, combining drilling data with observation and analysis of well core, The lower of the third member of the Shahejie Formation can be divided into four kind of sedimentary systems such as braided delta, fan delta, delta and lake by using sedimentary facies signs which is rock feature, sedimentary structure, well log and section texture, each of the sedimentary systems and subfacies are described and generalized in http://www.chinamagnets.biz detail. At last, I concluded that the lower of the third member of the Shahejie Formation mainly developed shallow lake and delta sedimentary systems of Dongpu sag. On the basis of the analysis above, I deduce one sedimentary models of the Dongpu sag in the lower of the third member of the Shahejie Formation in Paleogene.On basis of structure-sedimentation evolution and distribution of sedimentary facies in Dongpu sag, combined with the characteristics of heavy minerals combination, characteristics of rare earth element and trace element, the planimetric distribution of sandstone and lith-facies, the lower of the third member of the Shahejie Formation’s palaeogeographical pattern are analysed, and four resource areas are divided, which located at the Western, East, North and Southeast of the basin.According to the forerunners’ data, combining the investigation of sedmentary system and the source of the sandstone bodies, lithofacies-paleogeography map working out. In the end, I expound the plane-topology rule of sedimentary facies in the different period and the planimetric distribution of the good reservoir sandstone, and point out the favorable accumulation area belt.