The Study Of Sequence Stratigraphy And Sedimentary Characteristics Of Ordovician Period In The North Slope Of Tazhong Area In Tarim Basin

In this paper,the study area is the north slope of Tazhong area in Tarim Basin,located in the central part of the Tarim Basin.The structural position belongs to the footwall of Tazhong No.1 fault,located in the north slope of Tazhong uplift zone.The purpose layer is Yingshan Formation and Penglaiba Formation of Lower Ordovician in Paleozoic.Considering the exploration situation of the study area,based on the sequence stratigraphy,structural geology,sedimentary petrology,deeply discussed the rock types,sedimentary facies features,sequence stratigraphy characteristics and reservoir characteristics.Combined with the seismic data,logging data and the single well sequence data,established the sequence stratigraphic framework,studied the distribution of sedimentary facies in the sequence framework,used system tract as a unit to draw the Seismic facies and sedimentary facies planar graph,analyzed the main control factors and laws,Summarized the sedimentary model,and preliminary study on the sequence framework of the reservoir characteristics,analysis on the relationship between the sequence boundary and different stage of karst.Influenced by the early Caledonian Episode II,the middle Caledonian,the late Caledonian and Early Hercynian period,the Ordovician north slope of Tazhong area has experienced the process from tension to compression.The early Caledonian Episode II in study area is weak;in the middle Caledonian episode I,squeezed by the South,tazhong area has uplifted.But because of relatively low uplift,the denudation degree in study area is also low.With the interaction of the middle Caledonian Episode II and Early Hercynian tectonic movement,Tazhong No.1 fault belt no longer active.Due to the background of the Carboniferous-Permian period of tension,Tazhong fault fold orogenic tend to stop,converted into extensional rifting and subsidence,so katake uplift underwater uplift State can be preserved.The middle Caledonian episode I movement made the southeast Katake Uplift have a strong extrusion from the south,study area thus uplift.By the difference of lifting,Katake Uplift lifting is stronger than Guchengxu uplift.With the common role in the subsequent middle Caledonian episode I,the late Caledonian and the Early Hercynian movement,the Ordovician structural high part of the study area suffered from different degrees of erosion.Tazhong North Slope Area in early Ordovician of the lower period of Penglaiba group-Yingshan group,the water is shallow,climate is dry,the study area developed limited platform sedimentary;In the middle Ordovician of the upper period of Yingshan group-Lianglitage group,water gets deeper,the climate becomes humid,the study area began to develop extensive platform sedimentary;in late Ordovician of the Sangtamu group,the sea level began to rise,the study area developed mixed continental shelf deposit.Based on the sequence stratigraphy,combined with the study of sedimentary background,the rock stratum,seismic stratigraphy analysis,identify 3 uplift unconformity sequence interface of the secondary,include SSB1~ SSB3,and 6 erosive unconformity sequence interface of the three levels,include SB2-SB4,SB6-SB8.The Ordovician system in the study area was divided into 2 second-order sequence(SSQ1~SSQ2)and 8 third-order sequences(SQ1~SQ8),6 four-order sequence.Based on the research of well profile and sedimentary facies,study on the sequence stratigraphic framework sedimentary facies and its controlling factors,Establish study area sequence and sedimentary evolution models.Finally form the sedimentary facies plan,and reveals the sedimentary facies distribution.The Ordovician of tazhong North Slope sequence formation and controling factors are tectonic subsidence,sea-level changes and paleo-climatic conditions.The main performance on the control function of tectonic movement is the influence in the sequence boundary and the sedimentary paleogeomorphology;Sea level fluctuation control the formation of three-level sequence boundary and succession of sequences within the system domain;Paleo-climate change is affecting the changes of carbonate platform facies types and locations.Tazhong North Slope area experienced the impact of multi period tectonic movement and sea level changes,form the different levels of sequence boundary,develop exposure and erosion discontinuous interface,corresponding to the different time,under different levels of corrosion develop different levels of corrosion.The corrosion level from small to large is divided into the following sections: the High advanced(four-grade sequence interface)syngnetic stage dissolution,low position stage erosion unconformity(three-grade sequence interface)syngenetic dissolution,dermatofibrosarcoma rise unconformity(secondary sequence interface)palewind gasification shell supergene stage karst,Orogenic angular unconformity(first sequence interface)palewind gasification shell long-termsupergene stage karst.High grade sequence interface corrosion can be superimposed on low level of sequence boundary corrosion.Influence of Tazhong North slope of Ordovician carbonate reservoirs is mainly controlled by sedimentary facies and sequence boundary.