Study On The Distribution Of Sedimentary System Of Dongying Formation Of Shengli Shallow Sea Area

Under the guidance of modern sedimentologic and stratigraphic theory,this thesis investigated the facies mark,sedimentary facies type and characteristic around Tanhai area of Dongying Formation,based on the longging,testing and seismic interpretation and so on,from332 exploration wells and 346.21 meters cores from 10 wells.Finally,establish sedimentary facies model,in combination with "point-line-plane" to analyze the vertical and horizontal development characteristics of sedimentary facies,summarizes the distribution of depositional systems and the evolution law.During the sedimentary period of Dongying Formation,the stratigraphic thickness in the study area was generally thin in the southeast and thick in the northwest.Under the background of sublacustrine environment as the main body of deposition,six types of sedimentary facies were developed from the bottom to the top,including sublacustrine fan,slump fan,fan delta,braided river delta and fluvial facies.Among them,sublacustrine fan is dominated by middle fan subfacies,which lithology is gray conglomeratic sandstone,medium-coarse sandstone and gray(black)mudstone,which can find the arctic-composite grain sequence,soft sediment deformation and imbricated gravel structure.the main body of slump fan is proximal lingual,which lithology is medium coarse sandstone,conglomerates and siltstones are observed,the common structures are slip-slump structures,synsedimentary faults and micro folds.The fan delta front is the main composition of fan delta,which lithology is mainly gray conglomeratic sandstone,gravel sandstone and siltstone,mudstone is mostly gray or brown,and the main sedimentary microfacies are debris flow deposit,braided underwater channel,river mouth bar and underwater braided interchannel.The former subfacies of braided river delta facies is dominant,the lithology is mainly medium to coarse gray(white)colored siltstone,the main sedimentary microfacies are underwater distributary channel,mouth bar and underwater distributary interchannel microfacies.The sublacustrine is mainly composed of shore-shallow sublacustrine deposits and(semi-deep)sublacustrine deposits,locally developed beach bar,which lithology is mainly medium-fine sandstone,siltstone,(argillaceous/calcareous)siltstone and gray or grayish black(calcareous)mudstone,the common sedimentary structures are various bedding structures such as horizontal bedding,parallel bedding and so on.The fluvial facies,from south to north,shows the distribution characteristics of braided river,branched river and meandering river,the lithology is mainly conglomerate,conglomeratic sandstone,medium-coarse sandstone,fine sandstone and mottled silty mudstone.During the depositional period of the Ed Ⅴ+Ⅵ sand group,shore-shallow sublacustrine deposits and(semi-deep)sublacustrine facies is the main sedimentary facies,around Kendong salient the fan delta front is developed.During the depositional period of the Ed Ⅳ sand group,fan delta front is the main sedimentary facies,(semi-deep)sublacustrine deposits characteristics were keeped around Zhuanghai area,with retention a little bit of slump fan;south part of Chengdao salient retention a small area of beach dam.During the depositional period of the EdⅢ2 sand group,sublacustrine basin contration,with fan delta front deposition is the main sedimentary facies,at the same time around Zhuanghai area and the south part of Chengdao salient inherited Ed Ⅳ sand group,the slump fan and beach dam sedimentary facies were keeped.During the depositional period of the Ed Ⅲ1 sand group,most part of study area developed braided river delta front subfacies,only around ZH101 well and Z104 well area retention characteristics of shore-shallow sublacustrine.During the depositional period of the Ed Ⅰ+Ⅱ sand group,study area shows obvious characteristics of fluvial facies,from south to north in turn present the transition of braided river,branching river to meandering river,areas around Zhanghai and Kendong salient the mid-channel bar microfacies of the braided river is developed,north part of Chengdao salient channel sandbars and crevasse splay were developed,multiple small sand beach were developed around east part of Chengdao salient.