Development Characteristics Of The Dongting Basin Yuanjiang Depression And Petroleum

Yuanjian depression which located in Dongting basin is one of the most deep, in seeking perfectly development of stratum, thickness of sediment and the most abundance of petroliferous characters . It is conterminous of the Huarong arch in the north and adjacent of Xuefeng mountain in the south, and in the east and west of the depression are Mahekou arch and Mupinghu arch. It is extend to along the direction of North-East, and its length is about 75Km while the width is almost 33 Km. And in this study , based on the main theories such as Plate tectonics, basin-mountion coupling development, organic origin of petroleum, sequence stratigraphy ,petroleum system along the main way of basin - source -petroliferous pool, the author focuses on the yuanjiang depression and the adjacent regional characteristic of tectonic evolvement; summarizes the relation of tectonic evolvement and the distribution of oil-gas in the depression; and the distributing disciplinarian of gas- oil. The main conclusions included:(1) The structure style,the feature of the tansmutation and formation between Dongting basin and Xuefeng-Mufu Orogenic belt are Synthetical analyzed, the author considers that there is extreme coupling between the Orogenic belt and basins in the diffirent periods from Meso to Cenozoic:1) The early and middle stage of Yansha (J3-K1-2); 2) The late stage of Yanshan (K31 -2); 3 ) The early stage of Himalayan movement (form the late periods from the late Cretaceous to the Paleogene ) ; 4 ) The late stage of Himalayan movement(Neogene-Quaternary.) .(2) According to the analysis of the structural style of Yuangjiang depression, the author points out the southwestern of depression has take on the shape of rupture while the bestow in northeastern part.The depression can be despart into three main tectonic unites and nine secondary tectonic unites, each Basin-mountion coupling development can be experienced in such phase: â‘ The formation of so-shear rift basin in the stage of middle Cretaceous. â‘¡The formation of subsidence basin in the stage of late Cretaceous.â‘¢ The stage of subsidence of fault blocks overspread between Paleocene and Oligocene. â‘£The middle-late stage of subsidence of fault blocks shrink in late Oligocene ⑤The stage of subsidence in the Neogene-Quaternary.(3) The boundaries between the strata from Cretaceous to Tertiary in Yuanjiang depression and the adjacent area have been divided and correlated.(4) In Eogene, with the formation to passing away of the rifts, their depositional environment showed regular diversification as foothill-fluvial-lake-fluvial (-foothill), and almost all aqueous continental sediments were found here, and it reflected the perfect series of development of the yuanjiang depression.Two third class Sequence can be departed, it is â…¢₃ (E₁t - E₂y) .which developed in the period of fault subsidence-depression and â…¢₄(E₂h-E₂x)which develop the depression of the basin.(5) After analyzing the type and distributing discipline of sedimentary in Yuanjiang depression, the favorable source layer are located on the two deep low-lying area of Yuanjiang depression, main period of petroleum evolvement was Yuanjiang period of Eocene, and it control the distributing and size and quality of source. The Jingxiazhou fault block - fault anticline area are the most favorable petroleum gathered and preserved area where having the better combination of source,reservoir and cap-rock for that they are abut against the central of source of deep low-lying and the best place where developing the better reservoir such as sandstones and baiyun stones, and for another there been a lot of structual traps such as fault...