Research On The Sedimentation Feature And Regularities Of Sand Body Distributions Of Three Sand In The Fourth Member Of Shahejie Formation In Yi176 Area,Bonan Depression

Bonan sag is located in zhanhua sag in the north of jiyang depression.The study area is located in the eastern segment of the downdip plate of chengnan fault,bounded by chengnan fault and adjacent to chengdong uplift.In this paper,the bohai sea south sub-sag,just 176 block well logging,mud logging,core observation data,a comprehensive analysis by sequence stratigraphy,sedimentology,such as discipline theory as the instruction,by identifying split sand body bottom interface and phase transformation of lithology and lithofacies,surface and lake sequence boundaries,flooding surfaces such as sand clear four on the section through three group of sequence stratigraphic classification scheme,on this basis to four on the section through three groups from bottom to top is divided into three level 4 SQ1,for SQ2 and SQ3 sequence.Among them,the SQ1,SQ2 and SQ3 sequences can be divided into water-entering system domain(TST)and high-order system domain(HST).During the SQ1 deposition period,there was no sedimentation and the strata were not developed in the southwest of the study area.The sedimentary strata in the middle of the study area are the thickest,up to 40 m.The eastern and eastern regions are relatively small compared with the central region,with a deposition thickness of about 20 m.During the SQ2 deposition period,the deposition in the middle of the study area was the least,with an average deposition thickness of about 15 m.The other Wells have little difference in formation thickness,which is about 30 m.During the SQ3 deposition period,the thinest stratum was located in the southwest of the study area,which was only 12 m.During the SQ3 period,the sedimentary strata in the well area in the southwest were generally small,while the sedimentary thickness of the strata in other areas was about 30 m.In the study area three sections on the section through three sand lithofacies data,log data,core data such as data analysis,combined with the regional background of sedimentary characteristics,points out of the yongjin area in three parts on the section through three sand group as a set of lacustrine facies(coastal and shallow lake facies),nearshore subaqueous fan facies(fan,fan,fan subfacies)and delta facies,fan delta front subfacies deposition,fan delta front in three parts on the section through the advantage of phase 3 sand group.Microfacies mainly include underwater distributary channel,underwater distributary channel,distributary estuary dam,sand dam,beach dam,interbank,braided channel,braided channel,main channel,fan end mud,etc.According to the understanding of the sand body plane distribution in the study area,during the SQ1 deposition period,the underwater branch channel sand body was the most developed,with the thickness ranging from 6 to 10 m,and the distribution range was wide in the northwest of the study area.The thickness of the subaqueous fan sedimentary sand body near the east coast is between 6-10 m.During the SQ2 deposition period,affected by the source of uplift in the chengdong uplift in the north,the distribution range of the sand body was narrowed to the north,with the thickness between 4-8m,and the overall sand body thickness of the offshore underwater fan in the east became thinner,with the thickness between 4-6m.During the SQ3 deposition period,the sand body scope was further reduced.Until the SQ3 HST period,only the sand bodies around well 283 in the north,well 176 in the west and well 179 in the middle were more than 4m thick,isolated and disconnected from each other.