High Precision Sequence Stratigraphy And Sedimentary Facies Of The Third Member Of The Paleogene Dongying Formation In Bozhong Sag,Bohai Bay Basin

The Bozhong depression is rectangular as a whole and it includes several sub-sags.It is the main sag of Bozhong depression and the largest hydrocarbon-generating sag in the Bohai Sea.The third member of Dongying Formation is not only the source rock section of Bozhong Sag,but also the important oil-bearing strata.The study on the distribution pattern of lacustrine source rocks in the third member of Dongying Formation should be based on sequence framework and sedimentary system,while the early research on lacustrine source rocks was mostly limited to the third-order sequence framework,and there was no matching and comprehensive analysis of high-precision sequence stratigraphy,sedimentary system analysis and geochemical data of source rocks,so this paper mainly focused on fine-grained sediments with high-precision sequence and sedimentary systems.further research in the region east three sections of high resolution sequence and sedimentary system not only lacustrine source rocks in the bohai sea region research direct guiding significance,but also enrich the sag in bohai region sequence and sedimentary system of research,and has good reference value to sedimentary system research of deep lake.Guided by the theory of sequence stratigraphy,sedimentary petrology and seismic sedimentology,the high-precision sequence stratigraphy and sedimentary facies of the third member of Dongying Formation in the study area are studied from"point"to"line"and then to"plane".The characteristics of high-precision sequence stratigraphic framework and development of sedimentary system in Bozhong sag of Bohai Bay area are clarified through research.Based on the theory of high-precision sequence stratigraphy and interface recognition characteristics of the fourth-order sequence of paleontology,well logging,lithofacies,clay minerals,geochemical indexes and seismic profiles are established,and two fourth-order sequences and four five-order cycles are identified in the third member of dongying formation.The study on the plane characteristics of high-precision sequence strata in the eastern third member of the study area shows that the SQd3~1sequence and the SQd3~2 sequence are thick and widely distributed throughout the region.The SQd3~1 sequence is thick in the southeastern part of the study area,and the SQd3~2 sequence is thick in the southern part of the study area.Using sedimentology and seismic stratigraphy to establish the identification mark of sedimentary system in the study area.And it is believed that braided river delta,fan delta,lake and sublacustrine fan sedimentary systems are mainly developed in the three members of dongying formation.And shore-shallow lake and semi-deep lacustrine sub-facies were mainly developed in the lake sedimentary system.Application,On the basis of single well sedimentary facies analysis,the seismic attributes analysis in the study area and seismic facies identification method together,and then in the study area east three internal level 4 sequence of sedimentary facies distribution of the locations on the plane to explore,in this,SQd3~1sedimentary period,the main development half deep lake-deep lake sedimentary subfacies,in the central in the study area mainly developed littoral and shallow lake sedimentary,near the northern raised primarily in the fan delta and braided river delta sedimentary system,SQd3~2 sedimentary period,the overall main littoral and shallow lake sedimentary subfacies,From shore-shallow lake deposits to semi-deep lake-deep lake-like deposits in the middle to the surrounding areas.