Study On Sedimentary Facies Of The Middle Part Of The Third Member Of Shahejie Formation In Liutun Sag,Dongpu Depression

Through integrated analyses of the core,well log,mud log,and seismic data,this thesis applies principles of sedimentology,well log geology,and sequence stratigraphy to classify sedimentary facies,construct high-resolution sequence stratigraphic framework,interpret depositional systems,delineate sandstone distribution patterns,and predict potential hydrocarbon exploration targets within the middle part of the Third Member of Shahejie Formation(abbreviated as middle Es3)in Liutun Sag,Dongpu Depression.In the study interval,13 sequence stratigraphic surfaces are recognized,including 2 second-order surfaces and 11 third-order surfaces.Within the sequence stratigraphic framework,the study interval contains 12 sandstone beds,which can be further divided into 26 layers.The middle Es3 is composed of conglomerate,medium sandstone,siltstone,mudstone,and evaporite,within which interbedded mudstone and siltstone/argillaceous siltstone is dominated.The evaporite is regionally continuous in the northern portion of the study area,but absent in the south of Well h96.The sedimentary structures of the siliciclastics include ripple mark,tabular and trough cross stratification,planar,parallel,and massive bedding,as well as soft sediment deformation and convolute bedding.The compositional and textural maturity of the deposits in the west portion of the sag are relatively high.They are interpreted as braided delta depositional systems,containing subaqueous distributary channel,sheet sand,channel mouth bar,and interdistributary bay subfacies.The compositional and textural maturity of the deposits in the east portion of the sag are relatively low.They are interpreted as turbidite fan deposition system,containing subaqueous channel and fan lobe subfacies.The lacustrine deposition systems is regional developed,including littoral and sublittoral-profundal lake.The evaporite only occur in profundal lake.The middle part of Es3 in the study area formed during lake regression,reflected by the overall fining-upward trend.The braided delta deposits in the west part of the sag is laterally continuous,whereas the turbidite fan deposits in the east part of the sag is locally developed.Subaqueous distributary channel and sheet sand deposits stack vertically.Overall the sandstones have a fan geometry in plane view.Finally,potential hydrocarbon exploration targets within the m10 sandstone beds of the study area are predicted on the basis of analyses of depositional systems,seismic attribute,and sedimentary facies distribution.