| The Ordos Basin is a polycyclic superposition basin as well as the largest sedimentary basin on land in China which possesses abundant oil&gas resources and have feeble crogenesis. It has been becoming one of the important tactical areas in oil&gas exploration and exploitation in China.. Ansai Oilfield is located in the slope of Shanbei of the Ordos Basin. The main oil-bearing layer is Jurassic Yan 'an Formation, and it was formed on the background which is the temporary uplift of indosinian movement. It is significant that the exploration of petroleum resources to changqing oilfield. It is necessary to do particularity reasrearch for the sedimentary facies and accumulation oil&gas disciplinarian in order to research the disciplinarian of accumulation oil&gas.On the basis of the throries of sedimentary facies and petroleum geology, combined with the date of field sections ,outcrop ,cores and other geological materials, the paper research provenance , the types of sedimentary, sedimentary facies belts, distribution of the sandbodies, rebuilding paleogeomorphology etc. Further understand the sedimentary system of Jurassic Yan 'an Formation of Ansai Oilfield and the disciplinarian of accumulation oil&gas through the researching. Finally ,there were many prospective targets had been found.The strata of reaearching is Jurassic Yan 'an Formation, including oil layer yan-10, yan-9, yan-8, yan-7. Dividing oil layer yan-9 into yan-93, yan-92, yan-91,and dividing oil layer yan-8 into yan-83, yan-82, yan-81. Confirming the boundary of each stratum.and elaborating the litho-electric feature of each stratum in order to enable thin layer division more reasonable , accurate and lay a favorable basis for the sedimentary facies and disciplinarian of accumulation oil&gas of research district.From palaeo-structure pattern, distribution of sedimentary system, depositional structure and texture, composition characteristics of debris,characteristics of heavy minerals, sediment source of study area was discussed. It indicated that debris material of Yan'an Formation mainly derived from north and northeast part of the basin.Appling the method of cartography with single factor and dominance aspect, we have drawn contour line map of sand thickness, contour line map of ratio between sand thickness and stratum thickness. We discussed distribution characteristics of reservoir sand body and evolution of sedimentary facies and microfacies. And combining the field type section , lithologic characteristics, sedimentary structures, the sedimentary facies of single oil well and particle size analysis, we can determine that the layer Y-10 is braid river sedimentation and the layer Y-9, Y-8, Y-7 are delta deposit. The distribution of the sandbodies is controlled by sedimentary facies. Deltic subwater distributary channel sand body and river channel sand body are matrix sandbodies of reservoir model of Ansai Oilfield .Their spread direction is SN which formed as banding.The early Jurassic sedimentarywas a evolution process which was erosion, compaction,filling. Therefore, the sediment of Fuxian and Yan'an,their deposition thickness, lithologic characteristic, distribution characteristics of reservoir sand body and layer were controlled by palaeogeomorphology background. The stratigraphic sequence and the different combinations of sedimentary facies have distinct differences in profile which is useful for looking for the favorable zone. Though the comparing about different sections and combining with regional geology, researching palaeogeomorphology background, we can identify four primary palaeogeomorphology cell.including erosion valley, paleo heigh land and paleo uplift-brae and valley-downbend uplife.Synthetizing the reservoir quality,the sealing ability of cap rock, trap types, reservoir-forming model in order to analyze the disciplinarian of accumulation oil&gas. Ultimately, many favorable zones were examined.
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