The Falling Stage System Tract's Sedimentary Characteristics And Reservoir Significance Of Cretaceous Shushanhe Formation In Halahatang Sunken Of The Tabei Area

The Halahatang sunken is located in the central of the Tabei Uplift.The sedimentary strata of the Cretaceous Shushanhe Formation were studied in this paper.Based on the theory and method of sequence stratigraphy,sedimentology and other disciplines,the paper comprehensively analyzed the core,log curves and seismic data,studies the whole sequence stratigraphic sedimentary facies in the study area,and emphatically analyzed the sedimentary characteristics and favorable zones of the falling stage system tract in the study area.In the study area,the Cretaceous Baxigai Formation,the Shushanhe Formation and the Yageliemu Formation can be regarded as a regional secondary sequence.It can be divided into five third-order sequences according to the four transgression surface,which named SQ1,SQ2,SQ3,SQ4 and SQ5.For the whole Kapushaliang Group in the study area,SQ1-SQ5 is basically developed.In the secondary sequence of the study area,we can further divide it into low system tract,transgression system tract,high system tract and the falling stage system tract.The research focus on the falling stage system tract,which is basically corresponding to SQ5.The Cretaceous in the study area is a shallow lake basins,mainly includes facies of braided river,delta and shore-shallow lacustrine.In the early cycle,braided river and delta facies developed.In the mid cycle,lacustrine and delta facies developed.In the late cycle,the delta developed.In the falling stage system developed the delta front subfacies and the delta plain subfacies.The favorable zones in the study area are mainly developed in the delta front subfacies and the delta plain subfacies.The favorable reservoirs in the falling stage system are mainly developed in the underwater distributary channel microfacies and part of the delta plain subfaices.