Middle And Upper Juassic High-resolution Sequence And Sedimentary System Research In Junggar Basin, Xingjiang

Research area sets in Bogeda mountain fold belt foreland and Fukang fault zone in southern margin of east Junggar Basin, which is surrounded by depressions and abounds in hydrocarbon source rocks. Middle and Upper Jurassic stratigraphic reservoirs are mainly component of rivers and alluvial fan sandbodies. Structure-lithologic traps develop commonly and have good reservoir potential. High-resolution sequence stratigraphy and sedimentary system research is very important for oil and gas exploration in Santai area.Using high-resolution sequence stratigraphy principles and sedimentary working methods, paper identifies low-level cycles and middle-level cycles on basis of sedimentology in core and logging calibration, well then, gets the time-depth scale relation by synthetic seismic records to make strata comparison in wells-seismic profiles. Paper calibrates the sequence bounds in wells to confirm the strata comparison at last. Finally, the middle and upper Jurassic strata is divided into I , II long-term cycles and MSC1-MSC6 middle-term cycles, which correspond to the 6 members in Toutunhe formation and Qigu formation. Paper offers the evidences of base-level-cycle sequences and bounds.MSC1, MSC4 are unsymmetrical rise-base-level sequence style, formed by bottom continuous of braided channel sands and upper channels inter sediments. MSC2’s decline half-cycle is component of flood plains mudstone and crevasse-splays’s silty sands, its rise half-cycle is component of braided channel sands and channels inter sediments. MSC3 is unsymmetrical decline-base-level sequence style, formed by channel inter sediment of natural levee’s siltstone, flood plains and crevasse-splays’ fine sandstone. MSC5’s decline half-cycle is component of flood plains’ mudstone and fan margin’s fine grained sediments, its rise half-cycle is constituted by braided channel’s sandy conglomerate and cross flow’s silty in fan. MSC6 is unsymmetrical decline-base-level sequence style, formed by fan margin’s fine grained sediments, cross flow’s silty and braided channel’s sand gravel body in fan.In the stratigraphic framework, paper analyzes the sedimentary system’s faces exhibition and vertical evolution characteristics. Basing on drilling cores and log analysis and making the formation and sandstone isopach map, the paper identifies the braided fluvial river and alluvial fan and establishes logging faces mode. As the rise-base-level cyclic changing, braided rivers abound in MSC1& MSC2 and develop best in MSC2.Alluvial fan sediments in MSC1 south part locally. MSC3’s water becomes deeper and causes the flood plains and channel inter sediment larger. The braided river sediments in MSC4 are plentiful and the sandbodies connectivity is good. With the base-level declining, Source supply from the Beisantai salient becomes larger in MSC5 and MSC6, which leads to the development of alluvial fan in research area northwest. Main source supply comes from Santai salient in south east. The Beisantai salient is relatively weak as a source in early period and becomes stronger in Qigu formation. The ancient flow direction is from southeast to northwest.Many types of traps exist. River channel and alluvial fan sediments which communicate fracture or locate on Wuliangshan nose structure, Santai faulted anticline and central faulted nose structure are available for hydrocarbon gathering.