Study On Lime Mudstone's Distribution Characteristics Of The Lower Es₃ In Shengtuo Area Of Dongying Depression

Lime mudstone and sandstone have the similar seismic characteristics and well logging characteristics,so they can't be distinguished.The presence of lime makes an inaccurate sandstone description.The paper had studied on the lime mudstone's distribution characteristics and the development of the Lower Es₃ layer in Shengtuo area of Dongying depression,investigated the logging response characteristics of lime mudstone,used the methods of sedimentary cychicity analysis to do the stratigraphic classification and correlation of the Lower Es₃ in Shengtuo area of Dongying depression,which are combined with well logging,seismic,geochemical and other information,The main understandings are the following:The logging characteristics of lime mudstone have been summarized,which include conventional logging response characteristics,natural gamma-ray spectral logging,geochemical element content.Uranium element can distinguish 3lithologies,common mudstone shows the lowest Uranium content,sandstone shows the medium Uranium content,lime mudstone shows the highest Uranium content.Th-K crossplot can be used to separate lime mudstone from common mudstone.GR-AC crossplot can be used to distinguish lime mudstone,mudstone and sandy mudstone.Lime mudstone usually interactively develop with mudstone,sandstone developed,which had a diverse contact relationship with the upper and lower rock.According to the contact relationship with the upper and lower rock,lithofacies of Shengtuo area is divided into four types,the logging interpretation model is established.They are mudstone-sandstone type,mudstone-sandstone type,lime mudstone-mudstone type,lime mudstone–conglomerate type.According to the logging data and seismic data,the Lower Es₃ has been divided into 3 system tracts,highstand system tract,transgressive system tract and lowstand system tract.The lime mudstone distribution in every system tract had been analyzed.The lime mudstone distribution in highstand system tract is that from the the northwest to the deep lake area the thickness of lime mudstone gradually increased.The lime mudstone distribution in transgressive systems tract is that the thickness of lime mudstone in eastern area is thicker than lime mudstone in western area on the whole,in the eastern area,from north to the southeast the thickness of lime mudstone gradually reduced.in the western area,from the northwest to the southeast–east,the thickness of lime mudstone gradually increased.The lime mudstone distribution in lowstand systems tract is that from the northwest to the deep lake area lime mudstone's thickness increased,the thickest area distributed between the two distributed fan body.Sedimentary cychicity analysis is used to do the stratigraphic classification and correlation,combined with the partition plan of system tract,the Lower Es₃ is divided into 6 parasequence sets,which are S1,S2,S3,S4,S45,S6parasequence sets.There are four seismic facies in Shengtuo area.According to the study of amplitude and frequency characteristics,the conventional seismic property couldn't be used to differentiate sandstone from lime mudstone and three seismic property which can differentiate sandstone from lime mudstone better are selected.