Study On Sedimentary Characteristics And Lithofacies Palaeogeography Of Early Permian Taiyuan Formation In The Eastern Ordos Basin

Ordos Basin is a large-scale superimposed basin rich in oil and gas in China.After years of exploration and practice,oil and gas shows have been found in several formations of the basin.Taiyuan Formation in the basin is a transitional facies environment of land and sea,with multi-layer coal measures,carbonaceous mudstone and sandstone layers,which have good hydrocarbon generation and storage conditions of source rocks.Although previous studies have been carried out on the upper Paleozoic in the eastern margin of the basin,the sedimentary characteristics,sedimentary facies types,sequence stratigraphic framework,sedimentary system and sedimentary model in the sequence framework of Taiyuan Formation in Suide-Wubu area in the eastern margin of the basin are relatively low.Combined with previous studies,this paper aims at the current situation of low research level of Taiyuan Formation in the eastern margin of Ordos Basin,and further study on the sedimentary system of Taiyuan formation has a strong theoretical and practical significance.In this paper,through the study of the depositional system and stratigraphic sequence stratigraphic framework of Taiyuan Formation in the eastern area,and through the means of drilling cores,well logging data and well connection correlation,the lateral and vertical distribution characteristics of the sedimentary facies of Taiyuan Formation in the study area are studied in depth,and the sedimentary sequence framework of Taiyuan formation is built.Based on the analysis of the sedimentary system of Taiyuan formation,sequence stratigraphic framework and the sedimentary system within the sequence stratigraphic framework,the sedimentary model of Taiyuan formation is constructed,which lays a solid geological theoretical basis for deepening the exploration and development of oil and gas in the region and improving the oil and gas production of the basin.Based on the study of petrology,sedimentary structure,paleontology and well-connection section,shallow sea shelf facies and barrier coast facies are mainly developed in Taiyuan Formation in the study area.Combined with previous studies,this paper summarizes that there are obvious differences in plane sedimentary faciesbetween the north and south,East and west of Taiyuan formation.Delta plain facies is developed in the north of the study area,shallow sea shelf facies carbonate deposition is mainly developed in the Middle East and south,tidal flat facies is developed in the west,lagoon facies and barrier island facies are developed in the central area.The vertical change of Taiyuan Formation in the study area is relatively small,whose upper part is mainly shallow sea shelf carbonate deposit,with lagoon facies deposit,and the lower part is mostly barrier coastal tidal flat deposit,with coal seam,carbonaceous mud(shale)and other lagoon deposits.Based on the study of sedimentary facies,this paper studies the sequence framework of Taiyuan Formation in the study area,and summarizes three types of short-term sequence stack,which are retrograde type,progradational type and aggradational type.Taiyuan Formation in the eastern part of the basin is divided into one long-term sedimentary cycle and four middle-term sedimentary cycles.Through the establishment of drilling sedimentary sequence framework in different areas,the distribution of sequence stratigraphy in the study area is studied in detail,the difference of sequence framework between the East and the west of the study area is summarized,and finally the sedimentary cycle sequence framework of Taiyuan Formation in the study area is established.