The Sedimentary Characteristics And Accumulation Rules Of Chang 8 In Zhuang 36,Heshui Area,Ordos Basin

Block 36 in the Heshui area is located in the southwest of the Ordos Basin,structurally belonging to the Gucheng nose uplift on the northern Shaanxi slope.This paper takes the Chang 8 oil layer group in the Zhuang 36 block in the Heshui area of the Ordos Basin as the research object.On the basis of previous studies,it takes core identification,logging facies identification,oil-water identification,and reservoir-forming element analysis as clues,in the fine stratum On the basis of division and comparison,and sedimentary microfacies analysis,the distribution characteristics of oil reservoirs in the study area are summarized,the main controlling factors of oil and gas accumulation are analyzed,and the law of oil and gas accumulation in this area is finally clarified.The main knowledge obtained is as follows:1.Select typical wells,assisted by marker layers,and integrated drilling and logging and other markers to determine the stratigraphic division and comparison plan of the Chang 8 oil layer in Block Zhuang 36 in Heshui area,and re-divide the key layers to divide the Chang 8 oil layer.The group is divided into length 8₁and length8₂layers,length 8₁is subdivided into 3 small layers of length 8₁¹,length 8₁²and long8₁³,and length 8₂is subdivided into 2 small layers of length 8₂¹and length 8₂².This scheme can be used in the whole Make reasonable comparisons between districts.2.Through comprehensive analysis of core and logging data,a typical sedimentary facies sequence was established.The study area mainly developed delta front deposits,and further divided three types of sedimentary microfacies:underwater distributary channels,distributary bays,and estuaries.The corresponding sedimentary microfacies model was established on the basis of detailed research on the characteristics of small sedimentary microfacies and sedimentary evolution law of Chang 8 oil layer in Zhuang 36 block in Heshui area.During the 8₂-year period in Zhuang 36 block of Heshui area,the lake level rose rapidly and the shallow lake area continued to expand.During the Chang 8₁period,the lake level rose slowly,and the source area provided sufficient sources,and the underwater distributary channel microfacies developed extensively.Therefore,the delta front sand bodies developed during the Chang 8₁period.3.The thick source rock developed in the Chang 7 layer of the Zhuang 36 block in the Heshui area is the main oil and gas source of the overlying Chang 8 oil layer.On the plane,oil and gas are mainly distributed in the northwest,middle,and southeast of the work area.The northwest and southeast oil and gas are distributed in strips,and the middle is distributed in sheets.The horizontal distribution surface of the oil reservoir is mainly controlled by the distribution of sand bodies,which mainly extends along the northwest-south east direction.The main factors controlling oil and gas accumulation in Chang 8 of Block Zhuang 36 in Heshui area are the distribution of sedimentary sand bodies,the quality of reservoir physical properties,and the quality of source rocks.4.Structural traps are not developed in the work area,with micro-fractures and few faults.Lithologic oil reservoirs are developed in this area.The reservoir types mainly include lens reservoirs,sand body updip pin-out reservoirs,and impermeable layer physical barrier reservoirs.The dominant transport system in this area is the well-developed micro-fractures and sand bodies with small differences in physical properties and good connectivity.