Sedimentary Characteristics And Control Factors Of Zhujiang Formation In The Northern Slope Of Baiyun Sag,pearl River Mouth Basin

Northern South China Sea is an important area for oil and gas exploration in China.With the gradually depended of oil and gas exploration,shallow continental shelf has been difficult to meet the increasing demand for oil and gas resources.As a large reservoir,the shelf margin delta and basin-floor fans have drawn more and more attentions.Due to the existence of large delta and basin-floor fan reservoir is becoming a hot spot of oil and gas exploration areas in the Shelf slope zone of Northern slope of Baiyun sag,pearl River Mouth Basin.Under the guideline of seismic sedimentology,sequence stratigraphy,sedimentary system analysis and sedimentary hydrodynamics,using high-resolution 3-D seismic data,drilling and logging data covering whole Baiyun Sag,we make the following achievements.On the basis of ascertaining the slope break type and distribution regularities of Zhujiang formation in the Northern slope of Baiyun Sag,Pearl River Mouth Basin,we build a high resolution sequence stratigraphy framework.Through the analysis of sedimentary system,we confirm the temporal and spatial relationship of sequence architecture and sedimentary.Through the paleogeomorphic restoration of synsedimentary tectonic,we confirm the control of sedimentary on the shelf slope break.We finally reveal the inner link among within the isochronal stratigraphic framework of the sedimentary facies,structural slope belt or construct the ancient topography and provenance supply system,elucidate the mainly control factors on spatial heterogeneious distribution in the system tract.And construct a spatial-temporal evolution sedimentary model of sedimentary system,which facilitates future hydrocarbon exploration.The main achievements of this paper are as follows:1.Based on the high-resolution 3-D seismic data and drilling and logging data,multistage fracture slope break has been justified of Zhujiang formation in the Northern slope of Baiyun Sag,and has elucidated its spatial distribution.In the SQzj1(23.8Ma-21Ma),the shelf break is located in the southeast of the study area.In the SQzj2(21Ma-17.5Ma),because basement subsidence of the Baiyun movement,shelf slope north moved to Panyu low uplift,and the multistage fracture slope break.Except the shelf slope break,in slope,first-order slope break and secondary slope break can be divided by two echelon fractures.The study area can be divided into continental area,upper slope area,udder slope area and deep-sea plains by the shelf slope break,first-order slope break and the secondary slope break.Shelf slope break belt restricts the change of basin filling accommodation,which affects the distribution of the sedimentary system.2.Sequence interface has been identified;the characteristics of reflection interface have been found out,the high resolution sequence stratigraphy framework and have constructed a sequence structure model have been confirmed of Zhujiang formation in the Northern slope of Baiyun Sag.Tied by the division of 17 wells of sequence stratigraphic,multiple well tie and 3D seismic data,3 sequence boundaries SB23.8,SB21 and SB17.5 are identified,and Zhujiang formation can be divided into 2 Third-order sequences,i.e.SQzj1 and SQzij2.FFS and MFS18.5 can be identified in the SQzj2,which can be divided into lowstand systems tract,transgressive systems tract and highstand systems.Constructed under the slope breaks control mode of sequence development,in the SQzj1,only highstand systems can be discriminated,the southeast slope control the development of slope fan.In the upper slope area of SQzj2 develop delta sedimentary,first-order slope break control the udder slope area of the slope fan sedimentary,and secondary slope break control the deep-sea plain of sea-floor fan sedimentary.3.The distribution of sedimentary system has been found out,and a spatial-temporal evolution model of sedimentary system has been constructed,in Zhujiang formation in the Northern slope of Baiyun Sag.Shelf margin delta sedimentary system the most typical in west has developed the depression transformation of shelf margin delta-channelized fan-sea-floor fan.The shelf margin delta is controlled by shelf break and the single source supply from north.Under the control of first-order slope break,shelf margin delta secondarily transports formation for channelized fan.Under the control of secondary slope break,channelized fan thrice transports formation for sea-floor fan.Channelized fan has developed the depression transformation of shelf margin delta-slope channel-channelized fan-sea-floor fan or grey matter channel,in east the most typical.The shelf margin delta is controlled by shelf break and the numerous source supplies from northeast.Under the control of first-order slope break,slope channel of high-angle secondarily transports formation for channelized fan.Under the control of secondary slope break,channelized fan thrice transports formation for sea-floor fan.4.It has been proposed here that the basin structure,the ancient landform and sediment supply are the main factors controlling the evolution of sedimentary systems in Zhujiang Formation,Baiyun Sag.(1)Basin structure,23.8-21 Ma belongs to fault depression stage,with the severe and generally high active index of synsedimentary faulting.During 21-17.5Ma,the fault activity decreased significantly,but a few fracture last activities under the regional tectonic background.Long-term activities of synsedimentary faults form the multistage tectonic slope-break,which restricts the basin filling of accommodation space.(2)Aancient landform,palaeogeomorphology controls the sand disperse system and facies differentiation of lowstand system tract.During SQzj1,the ancient landform main control slope fan in the southeastern.During SQzj2,the shelf break is located in the north of the study area,which control the shelf margin delta.First-order slope break control the channelized fan by secondarily transportation formation.Secondary slope break control the sea-floor fan by thrice transportation formation.And slope is much smaller than the eastern slope in the west,result in delta with is the background source for sedimentary by slope channel transportation to the udder slope area and the eastern of channelized fan and sea-floor fan size and distribution range is bigger than the west.(3)Sedimentary supply,the west sedimentary mainly come from Paleo-pearl river with the single source sand filling.The east is numerous source supplies from Dongsha uplift with northeast direction and content of sand body.