Dentative Discussions on Depositional Facies Model of Braided Stream in the Northwestern Margin,Junggar Basin: Acase of braided stream deposition of Badaowan Formation,Lower Jurassic in No.7 Area

Braided-stream deposits are the major depositional system of lower Jurassic in the northwestern margin,Junggar Basin.Based on observation and description of cores,thin-section identification,assay and analysis,and well logging of Badaowan Formation,lower Juassic in No.7 area of Xinjiang oil field,the depositional markers' features of braided stream were generalized in which rock types are simple such as;the maturity of rock is low;rock compositions are complicate;plant residue carbides locally concentrate into stratiform;sedimentary structures are plentiful;there is a dual structure that a top layer and a bottom layer vertically overprint and many sand-bodies form pan communicated sandbody.This parper further analysed the changes of color,rock,granularity,sedimentary structure and logging responses in vertical depositional associations of braided stream,which is interpreted as a sequence of channel lag deposit,mid-channel bar and flood plain.Using the spatial distribution of microfacies,it summarized the facies model of braided stream of Badaowan Formation,lower Juassic in No.7 area.These results have vital significance for progressive exploration and adjusted development of oil field.