Study On The Sedimentary Microfacies Of The Upper Wuerhe Formation Of The Permian In The M Area,Mahu Sag,Junggar Basin

Under the guidance of sequence stratigraphy and sedimentology theory,using the core,logging,well logging and seismic data of the study area,the stratigraphic framework of the Upper Wuerhe Formation(UWF)in the M area of the Mahu Sag,Junggar Basin was established.The spatial distribution characteristics and main sedimentary facies types of the sand groups under the sequence control of the UWF were identified,and the spatial distribution characteristics of the sedimentary systems of the UWF in the M area of the Mahu Sag area were identified.The research results obtained mainly include the following:1.The Permian UWF in the M area of the Mahu Sag developed three mid-cycle MSC1,MSC2 and MSC3 from bottom to top.MSC1 is the reference plane ascending half cycle,and MSC2 and MSC3 are the reference plane ascending half cycle and reference plane descending half cycle.Among them,MSC1 is subdivided into P3w13,P3w12 and P3w11 sand groups from bottom to top,MSC2 is subdivided into P3w21 and P3w22 sand groups from bottom to top,and MSC3 is divided into P3w3 sand group.The lithological assemblages in the sand groups can be summarized into the following four types: sand conglomerate + mudstone,sand conglomerate + gravel coarse sandstone + medium fine sandstone + mudstone combination,gravel coarse sandstone + medium fine sandstone + mudstone and pure mudstone section.In general,the UWF of the Permian in the M area of the Mahu Sag has undergone a base-level change process of rise-fall-rise-fall-rise.2.There is a certain difference in stratum thickness and distribution range of each unit of UWF of Permian in M area of Mahu Sag.Among them,the P3w13 and P3w12 strata in MSC1 have relatively thin remaining thickness in the northeast strata of the study area.In terms of deposition thickness,P3w22 has the largest deposition thickness,reaching a peak of 58 m near the Ke81 well.In general,the stratum thickness of each layer is thick in the south and thin in the north.3.The S Wuerhe Formation of the Permian in the M area of the Mahu Sag mainly developed alluvial fan facies,fan delta facies and lacustrine facies.The alluvial fan facies identified three subfacies: fan root,fan mid,and fan margin,and fan delta recognized two subfacies,fan delta root and fan delta front.The lacustrine facies mainly recognizes two subfacies: the shore shallow lake facies and the semi-deep lake facies.4.The sedimentary systems of different sand groups of the UWF of the Permian in the M area of the Mahu Sag show different characteristics.MSC1's P3w13 and P3w12 sand groups mainly developed alluvial fan facies deposits,while P3w11 mainly developed shore shallow lake subfacies deposits.The two sand groups P3w22 and P3w21 of MSC2 mainly developed fan delta facies and lacustrine facies.The fan delta facies is mainly developed in the area south of Well Mahu 1,and presents a pattern of retrogradation in the vertical direction.On the northern edge of the study area,shoreline shallow lake subfacies deposits are mainly developed.In MSC3,semi-deep lake subfacies deposits are mainly developed in the study area.