Study On Geological Model Of The Middle Es₃ Within The Liutun Sag,Dongpu Depression

The middle part of the Third Member of the Shahejie Formation of the Liutun Subsag,Dongpu Sag,has developed braided river delta front-beach bar-turbidite fan systems,which are oil and gas and exploration targets.A large number of interbedded sand and mudstone reservoirs are developed in the study area.However,confined by the low resolution seismic data,it is difficult to characterize sandstone distribution,which adds difficulty to the exploration of lithologic reservoirs in the current study areaThis paper focuses on the middle Es3 in Liutun Subsag of Dongpu Sag,aiming to identify lithology,establish lithology combination model according to the stacking style through analyzing core,mud log,well log and seismic data.Based on the division of sedimentary facies types,attribute fusion is applied to predict the distribution of different lithological combination models.The main conclusions are as follow:The established lithology combination models are mainly composed of thin-laminated sandstones,medium and thick-bedded sandtones,composite sandstones,and mudstones.They also contain a number of sand-shale lithology sub-categories.The combined lithologic models developed in the middle Es3 of the study area are mainly composed of thin-bedded sandstones,middle-layered sandstones,thick-bedded sandstones,composite sandstones,mudstones models.They also contain a number of sand shale lithology model sub-categories.The petroliferous m8 and m10 sandstone units in the study area are mainly composed of thin interlaminated sand and mudstone,muddy sandstone,sandstone composites,medium interbedded sandstone and mudstone,and thick-medium sandstone.The five lithology combinations have distinctly different well logging response characteristics.The thin interlaminated sandstone and mudstone and the muddy sandstone have high SP,GR,AC,and low DEN values.Sandstone composites and thick-medium sandstone are characterized by low SP,GR,AC,and high DEN values.The interbedded medium sandstone and mudstone,and the combined lithology of thin sandstone and mudstone laminae have medium GR,AC,and DEN values.The muddy sandstone exhibits low vibration and low frequency characteristics in RMS amplitude,instantaneous amplitude,and instantaneous frequency seismic sections.The thin interlaminated sandstone and mudstone has two seismic response characteristics,as low-vibration intermediate frequency and low-amplitude high frequency.The composite sandstone has the characteristics of high-middle and high-frequency vibrations.The interlaminated medium sandstone and mudstone is characterized by medium-vibration intermediate frequency,and the thick-medium sandstone is characterized by high-vibration intermediate frequency.The superposition of sedimentary facies maps and lithologic models shows that sandstone composites,thick-medium sandstone and high sandstone content combined models are mainly developed in subaqueous distributary channels and turbidite fans The potential exploration targets based on the model are located at the the center of Dongpu Sag and Hu 99 block.The thin interlaminated sandstone and mudstone and muddystone-intercalated sandstone are developed in the sublittoral-profundal lacustrine facies The other potential exploration targets are the Liutun Sag and Hu 99 transition zone and Hu 96 block.