Study On Sequence Stratigraphy Framework And Evolution Of Palaeogene In The 3^rd Structure Of Nanpu Sag

Located in the southeastern district of Nanpu Sag,the 3^rd Structure is mainly consisted of delta front and shore-shallow lacustrine sediment.There are problems such as confusing sequence division and unclear filling process of sedimentary sequence.Es1 reservoir is controlled by structure and lithology,with the characters of thin oil reservoir and unclear distribution.In view of the above problems,this article sets Palaeogene,especially focus on the Ed2-Es1,of the 3^rd Structure of Nanpu Sag as the research object and carries out the study of sequence stratigraphic and sedimentology with the combination of data of seism,well-logging,core,paleontology and so on.This study has established the sequence stratigraphic frame of Palaeogene strata,analyzed the gentle slope belt sequence stratigraphic characteristics and controlling factors,sedimentary evolution,distribution of lithological reservoir.It is important to guide the further exploration of lithological reservoirs.Knowledge and results obtained are as follows:?1?Four second-sequence boundaries,nine third-order sequence interfaces were identified in Palaeogene strata.Among these,Palaeogene is divided into eight third-order sequences,SQ3-SQ7 is divided into eleven system tracts;SQ5 is made up of four subsequence;and the lacustrine regressive system tract of SQ4 consists of two subsequence.?2?The Paleogene sequence boundary characteristics were clarified,and each sequence and system tract characteristics were analyzed.The sequence thickness from southwest to northeast shows a thickening and thick-thin-thick from northwest to southeast.The sedimentary thickness distribution of each system tract is controlled by a variety of factors,such as basin edge type,tectonic activity,sediment sources.?3?It is pointed out that the provenance is from the southwest of Shaleitian Salient in the study area,The type of sedimentary facies comprised fan delta depositional,braided delta depositional,shore-shallow lacustrine sediment and slump turbidite fan depositional.The fan delta and shore-shallow lacustrine sediment are mainly in SQ1 and SQ2,the braided delta and shore-shallow lacustrine or slump turbidite fan depositional are mainly in SQ3-SQ7.?4?The main controlling factors in the study area being summarized as tectonics,climate,provenance and lake level.Three kinds of sedimentary sequence structure styles being generalized as TST>RST?or HST?,TST=RST?or HST?,TST<RST?or HST?.Two types of sequence filling pattern were built: no slope belt sequence pattern and a slope belt sequence pattern,where no slope belt sequence pattern is the mainly sequence patterns for the study area.?5?It is point out that the study area contains three principal types of reservoirs,which are up-dip pinch-out sandstone out reservoir,lenticular sandstone reservoir,and structural lithological reservoir.The lithological reservoirs are mainly located in turbidite fan depositional of the low-stand system tract or lacustrine transgressive system tract,subaqueous distributary channel sand in lacustrine regressive system tract.