Analysis Of Sedimentary Facies In The Middle And Upper Member Of Shahejie Formation In Gubei Sag

The Gubei sag is located in the northeast area of the Zhanhua sag in the Jiyang depression,with an area of about 400km~2.It is a depression with a high degree of exploration,and the next step of exploration is to focus on stratigraphic lithological traps.On the basis of core,logging,seismic and analytical laboratory data,this study analyzed the sedimentary facies of the middle and upper submembers of the third member of Shahejie Formation in the Gubei sag,and determined the types and the distribution Characteristics of sedimentary facies.Therefore,it is of great significance to identify the distribution areas of favorable facies-controlled reservoirs and to form production blocks with a certain scale as soon as possible.By identifying typical sedimentary facies signs,the sedimentary facies in the study area are determined to be shallow water delta facies,fan delta facies,slump turbidite and lacustrine facies.Deltas are mainly delta front subfacies,including underwater distributary channels,estuary dams,and sheet sand microfacies;fan deltas are mainly fan delta front subfacies,including underwater distributary channels,estuary dams,and sheet sand microfacies;The lakes are mainly composed of shore-shallow lake subfacies and semi-deep lake-deep lake subfacies.Based on the high-resolution sequence framework,combined with paleomorphological analysis and provenance research,single-well facies and connected-well facies analysis were carried out,and the planar distribution characteristics of sedimentary facies and sedimentary microfacies of each sand group were clarified.According to analysis,the provenance mainly comes from Gudao bulge,Changdi bulge and Chengdong bulge.There are five provenance directions,mainly in the south,east,and southeast,and the northwest and northeast as supplements.The delta front of the gentle slope zone was separated on both sides of the uplift at the initial stage of deposition,and deposited extensively in the later stage,the scale of the sand body became smaller,and the distal end of the fan body collapsed to form turbidite.The scale of sand bodies in the eastern fan delta is increasing.The fan delta front in the northeast is prone to slumps in the eastern sub-sag,forming small-scale turbidites.The northwestern fan delta is a near source and short-distance deposit,and the fan plane distribution is narrow because of the steep slope topography.According to the development characteristics of topography and sedimentary facies,the deposition model of"shallow water delta+slumping gravity flow"in the south and the"fan delta+slumping gravity flow"deposition model in the east were established.Comprehensive analysis of the development horizon and development type of the favorable reservoir facies belt,combined with the reservoir physical property data,and based on this,predict the development location of the favorable reservoir area.Studies have shown that the sand bodies of the 2,3,and 5 sand groups in the upper Es3 sub-member are large in scale.The southern reservoirs from Gudao provenance have the best physical properties,followed by the long dike provenance in the east,and Chengdong provenance in the northwest is the worst.The underwater channel and estuary dam microfacies of the delta front and the underwater channel and estuary dam microfacies of the fan delta front are favorable reservoir facies belts.Based on provenance area,sedimentary facies,sand body scale and fault development,three favorable reservoir development areas are predicted with the distal end of the delta front and the distal end of the fan delta front as the main reservoirs.