Study Of Distribution Characteristics Of Lithofacies Of The Lower Es₃-upper Es₄ In Shengtuo Area Of Dongying Depression

A large number of limemudstone has developed in Shengtuo Area,it has an impact on the description of sandstone distribution.Although predecessors had studiedfine-grained sediments many years,there is no research about the comparison with sandstone and analysis,so the distribution of lime mudstone is not clear.The lime mudstone and conglomerate have the same seismic characteristics and well logging characterisitics,so the description of the sand is not accurate.The paper has studied on the the Upper Es₄ to the Lower Es₃ in Shengtuo area of Dongying depression,combined with results of previousstudies,core,logging,seismic,geochemical and other information are used multipurposely,studied the identification of the fine-grained sedimentary rocks of the objective interval in the study area.On the basis of stratigraphic division and correlation,studied the vertical and plane distribution rules of lithofacies combination types.The main understandings are the following:The main types of fine-grained sedimentary rocks of the Upper Es₄ to the Lower Es₃ in study area are:massive mudstone,medium-calcium layer lime mudstone,high-calcium layer lime mudstone,medium-calcium sandy belt lime mudstone,oil shale.The conventional logging data have a low degree of distinction of lithology.U can distinguish three lithologies,commonlymudstone shows the lowest U-value,sandstone shows the medium U-value,lime mudstone shows the highest U-value.Th-K crossplot can be used to separate lime mudstone from common mudstone.GR-AC crossplot can be used to distinguish limemudstone,mudstone and sandstone.Six types of lithofacies combinations in the study area are summarized as“lime mudstone pack sandstone”type,“mudstone pack sandstone”type,“mudstone pack lime mudstone”type,mixed type,“sandstone pack mudstone”type,“mudstone and lime mudstone are interbedded”type.And the corresponding model of logging response was established.The Lower Es₃ has been divided into highstand system tract,transgressive system tract and lowstand system tract.The Upper Es₄ has been divided into highstand system tract and transgressive system tract.According to the characteristics of the depositional cycle,the Lower Es₃ has been divided into six fourth-level sequences,SQ1 and SQ2 correspond to the highstand system tract,SQ3 and SQ4 correspond to the transgressive system tract,SQ5 and SQ6 correspond to the lowstand system tract.The Upper Es₄ has been divided into four fourth-level sequences,SQ1 and SQ2correspond to the highstand system tract,SQ3 and SQ4 correspond to the transgressive system tract.The distribution characteristics of lithofacies combinationof the Upper Es₄ to the Lower Es₃ in study area are:The lithofacies change frequently in the vertical direction,and the sandstone content and the lime mudstone content change rapidly,but the relationship between the two contents is trading off and taking tums.In general,the lithofacies in the east of the study area change frequently and complex,and the main lithofacies is the mixed type.The lithofacies change frequently in the horizontal direction,correlation is poor.The lithofacies in the west of the study area changed slowly,and the main lithofacies are“mudstone pack lime mudstone”type and“mudstone and lime mudstone are interbedded”type,and the lime content is higher than the west side.The litofacies change slowly in the horizontal direction,and generally can be compared between the wells.On the plane,the lime content in where between the two fan bodies is higher,and the main lithofacies is“mudstone and lime mudstone are interbedded”type,and in thetwo fan regions the other types of lithofacies are developed.