Study On Palaeogeography And Control Factor Analysis Of Efficient Reservoir Development In Late Paleozoic In Middle-eastern Ordos

Based on the identification of sequence boundary, the upper Paleozoic in the eastern part of Ordos are divided into 5 second-order sequences, eighteen third-order sequences and fifty system tracts. Further more, five second-order sequence filling modes are established, such as typeⅠin the basin with ramp margin and typeⅡin SQⅠ, SQⅡwith epicontinental sea background, meandering river - shallow-water delta sequence filling model in SQⅢwith decline and fall of epicontinental sea, braided river - the gentle slope-type shallow braided river delta sequence filling model, SQⅤmeandering river - lake delta sequence filling model.The character of main sedimentary facies, palaeogeographic distridution and evolution are discussed in sequence stratigraphic framework. 8 sedimentary facies, 18 Sedimentary subfacies and 23 Sedimentary microfacies are identified in upper Paleozoic in study area. Late Carboniferous the deposition pattern of carbonate tidal flat- barrier dams- lagoon- shallow-water delta is shown in study area and seawater is mainly from the direction of E and NE; early Early Permian the palaeogeographic pattern is formed which epicontinental sea sediments take the initiative, coexisting with meandering river- shallow-water delta- barrier dams- lagoon- carbonate tidal flat, seawater intrudes by the SE direction; late Early Permian meandering river- shallow-water delta-coastal lake mainly constitutes the Palaeogeographic pattern; Middle Permian, the deposition pattern of alluvial fan- braided river-delta– lake sediments is formed; late Late Permian, the palaeogeographic pattern is evoluted to meandering river - delta - lake, and the history of late Paleozoic sedimentary filling for study area is ended. The sedimentary filling in study area for late Paleozoic is divided into 5 stages, such as restricted epicontinental sea, development of epicontinental sea, decline and fall of epicontinental sea, coastal basin and inland basin.Under the guidance of activity theory, dynamic mechanism of palaeogeographic evolution is discussed with the infulence of screen activity of Hercynian movement. Source is from the Yimeng uplift , otherness uplift in source area is obvious, and characteristics of east-west division are taken on. It pointes out palaeogeographic evolution of late Paleozoic in study area, the spatial distribution of depositional system and changes in the direction of transgression are controlled by the combined effects such as restructuring of regional palaeostructure system triggered by changes in the form of plate collision, otherness uplift in source area, evolution of ancient features of sedimentary basin, intermittent extension resurrection of basement fault, regional sea-level changes. Based on the research of sedimentary basin development and evolution, relations with the northern belt, source characteristics, paleoclimate research etc, 5 structural- sedimentary filling models are established.Efficient reservoir development of Taiyuan formation in Shenmu-Shuangshan gas-bearing area is controlled by palaeogeography and structural framework, and related to the rock nature of source area, sea-level changes, diagenesis, intermittent activities of basement fault triggered by plate collision. Efficient reservoir development for member 8 in Xiashihezi fomation in Wushenzhao-Yijinhuoluoqi area is mainly controlled by nature of source and palaeogeographic pattern, and related to sequence filling model, diagenesis and late activities of north-east basement fault.