The Study Of Pinghu And Huagang Formation Sequence Stratigraphy And Sedimentation Facies Feature In Tianwaitian And Huangyan Region Of Xihu Sag,East China Sea

The north and south separately connected with Fujiang and Diaobei sunk,the east and west separately adjecent with the reef uplift and Diaoyu Island uplift ruche.The East China Sea Xihu sag Tianwaitian and Huangyan region structurally belong to Ningbo-Huangyan rooftop tectonic zone Xihu sag of east depression basin.it belongs to tertiary sedimentary basins of the Cainozoic era.The target stratum is palaeogene Eocene series-Oligocene Pinghu-Huagang FM.According to the present exploration situation of East China Sea Xihu sag Tianwaitian and Huangyan region and the difference of the division of sequence stratum and sedimentary system,based on the survey of regional structure,rely on theoretical direction of rock and biostratigraphy,this paper manages methods such as rock core,single well,logging,earthauake,combines with Sedimentology,Petroleum Geology,Reservoir Geology to make comprehensive research,divides single well sedimentary facies and sequence,compares well tie and seismic sequence stratum,summarizes the interfacial structure response,lithologic character and logging character to set up sequence stratigraphic framework,confirms the key formation interface of the sequence.Make sea-level change as a unit to compile sedimentary facies figure,study sedimentary evolution?or sequence evolution?.Based on this,use sedimentary reservoir geology theory,the core observation results and thin section identificationresultscomprehensivelytoanalyzerelationshipbetween reservoir-capping assemblage and sequence forecasting beneficial reservoir facies belts on basis of reservior space and reservoir physical property research.This paper,comprehensively analyzes biology,rock,and chronostratigraphy,combines with logging and seismic sequence,confirms the times and tectonic movement of Tianwaitian-Huagang region Pinghu-Huagang FM Xihu sag in East China Sea.Based on characteristic of sequence boundary,combines with research of fine calibrate well-to-seismic's seismic stratigraphy,it recognizes sequence boundary,and creatively divides Huagang formation in the research area into 3 third order sequence?previous reseachs recognize that Huagang formation should be divided into2 third order sequence—lower segment of Huagang formation is divided into 1 third order sequence,upper segment of Huagang formation is divided into one third sequence?on the basis of widely absorbing previous research achievements,the response of worldwide geological events and seismic facies analysis.The sequence division is that the previous reseachs'upper segment that is 1 third order sequence is divided into 2 third order sequence,so the Huagang formation in the Tianwaitian and Huangyan regoin of Xihu sag in the East China Sea is divided into 3 third order sequence?SQ4,SQ5,SQ6?,corresponding to its lower segment,middle segment,upper segment.It is important that this paper accurately recognize interface?T₂¹?between upper segment and middle segment.Pinghu formation s sequence division is similar to previous reseachs'research achievement.The reservoir type is humid fan-delta,so it is reverse cycle depositional order and top boundary is sandstone's or pebble sandstone's top surface.It is divided into 3 third order sequence?SQ1,SQ2,SQ3?,corresponding to its lower segment,middle segment,upper segment.In conclusion,the Pinghu-Huagang formation in the Tianwaitian and Huangyan regoin of Xihu sag in the East China Sea is divided into 2 second order sequence?SSQ3,SSQ4?,6 third order sequence?SQ1,SQ2,SQ3,SQ4,SQ5,SQ6?and flooding surfaces?MFS1,MFS2,MFS3,MFS4,MFS5,MFS6?,Each third order sequence is divided into the high system tract and the transgress system tract of sequence.Using lithology,sedimentary,paleontological characteristics,particle size analysis,logging features,heavy mineral and mineral composition analysis as the main indicator of dividing sedimentary facies,and combined with seismic facies analysis withine third-order sequences,this paper studies the sedimentary facies in Tianwaitian-Huangyan region,Xihu Sag.This area mainly develops wet fan delta system,whose subfacies spread from the west to the east.Because of the developing of this kind of facies,the sequences always consist of one or more anti-cycle deposition the system and its boundaries are always the top of sandstone layer.Based on the stratigraphy and sedimentary facies research and the core,paleontology,seismic facies,previous heavy mineral assemblage characteristics,mineral composition,the degree of structural maturity and compositional maturity analysis,we can find the decreasing of the pollen?oak powder?,large-scale progradation on seismic facies,increasing of structural maturity and compositional maturity degree from the west to the east,the combination of heavy minerals in western and central inversion of Xihu Sag have much difference.The reasons above can indicate that the source materials in Tianwaitian-Huangyan region mainly come from the western Haijiao uplift,it also has the possibility come from Yushan uplift.After the studying of sequence,and sedimentary facies,we have a comprehensive study on the sequence boundary of Xihu sag and the interface within second-order sequences and two-order sequence boundaries?uplifting unconformity?,third-order sequences?erosional unconformity?,three maximum flooding surface within third-order sequences are recognized.Through the establishment of the stratigraphic framework by the crossing-line well,sedimentary facies distribution within sequence of stratigraphic framework can be studied,and the main controlling factors can be preliminary analyzed,which can contribute to the studying of sequence-sedimentary development.Finally the depositional facies plane can be determined that can reveal the discipline of sedimentary facies.The Pinghu-Huagang formations develops of a total of 5 sets of reservoir-caps in Tianwaitian-Huangyan,Xihu sag.The reservoirs are SQ1-HST,SQ2-HST,SQ3-HST,SQ4-HST,SQ5-HST,SQ6-HST,whose porosity types are mainly intergranular pores.According to property analysis,SQ3-HST,SQ4-HST are better in longitudinal direction and the western gentle slope is favorable reservoir facies belt on the plane.Consolidated sedimentary sequence and reservoir characteristics and other aspects of analysis,thefavorablezonesofPinghu-Huangyanformatiomsin Tianwaitian-Huangyan region of Xihu sag are mainly located in the western gentle slope belt.