Sedimentary Facies Of The Fuxi Section Of The Paleogene In The Qu Tang Sub - Depression, Haian Depression, Subei Basin

Northern Jiang-su basin is large faulted basin, which has evoluted from Cretaceous to Quaternary period. The reacher area,which belongs to Qu-tang sub-Sags on the Hai-an Sag in Dong-tai depression of Jiang-su basin, located in Hai-an county, Jiang-su province. The target layer is in the third formation of Fu-ning group in Paleogene.Due to small scale and fragile structures developed and more fractures developed and various depositional conditions in Qu-tang sub-Sags, the degree of exploration and development of oil and gas in this area is still low, and the type of sedimentary facies and distribution feature are still unclear, so the result has been restricting and influencing directly further exploration and development in this area. By the basis of studying the regional geologic background in detail, this paper takes the theories of stratigraphic geology, as well as sedimentology as guidance.Combining the electric-logging data of21wells collected, the rock cores’feature of6wells observed, the stratigraphic division and correlation in Fu-ning formation could be done, so the type of sedimentary facies could be identified and the feature of sedimentary micro-facies could be analyzed prior to the distribution of the sedimentary micro-facies belts and the body of sand could be done.Making use of the features of lithology, E-logging and seismology, the formation of Fu-ning group is sub-divied into four members, what’s more, the E1f3is further sub-divided into four sub-members. The continuity of distribution of formation is excellent, the distribution of thickness is relatively uniform.The method of analysis of facies indicators is basis of study division of sedimentary facies and sub-facies. Basis on the analysis of sedimentary facies symbol in lithologic-facies which include colour, structure and construction, and electro-facies, the paper defines the third formation of Fu-ning group in study area mainly develops deposition of shore-shallow lacustrine sub-facies, what’s more, identifies the shore-shallow lacustrine mud micro-facies, the bar sand body and beach bar sand micro-facies.The development of sedimentary sub-facies and vertical depositional variation in the third formation of Fu-ning group could be analyzed. The variation characteristics in sedimentary sub-facies could be done through the section of wells. General speaking, the first sub-member in E1f3and the third sub-member in E1f3develop the bar sand body and beach bar sand well, but the continuity of sand is not good. The second sub-member in E1f3and the fourth sub-member in E1f3develop the shore-shallow lacustrine mud micro-facies well, but the bar sand body and beach bar sand are poor.Combining isothickness map of sand layer and contour map of ratio between sand and stratrum after analysis of single well and section of wells, the feature of sedimentary distribution in each sub-section which belongs to the third formation of Fu-ning group in study area could be done.Firstly, the fourth sub-member in E1f3belongs to deposition of shore-shallow lacustrine mud micro-facies.Secondly, the third sub-member in E1f3develops mainly deposition of shore-shallow lacustrine mud micro-facies. The bar sand body and beach bar sand micro-facies develops widespread distribution,where well Su-88, well Ji-H1, well Ji-7are. Thirdly, the second sub-member in E1f3belongs to deposition of shore-shallow lacustrine mud micro-facies. Finally, the first sub-member in E1f3develops both deposition of shore-shallow lacustrine mud micro-facies and the deposition of shore shallow lacustrine bar sand body and beach bar sand micro-facies,the places of well Ji-302, well Su-88, well Ji-7mostly distributes on the latter.