Development Characteristics of Sedimentary System and Control Factors Analysis of the Third Member of Liushagang Formation in Eastern Wushi Depression,Beibuwan Basin

Beibuwan Basin is one of the major oil-gas basins of the northern South China sea,where the third member of Liushagang Formation in eastern Wushi Depression is the main oil and gas exploration target layer.Therefore,its sedimentary model and distribution of sedimentary microfacies are the keys for the oil-gas exploration in this area.Through the comprehensive research of core,drilling,seismic data,this paper analyzes in depth the fault activity and its space distribution and characteristics of the sediment source system and the spatial distribution of the sedimentary micro-facies,and discusses the inter restricted relationship of tectonics and sedimentation.The results show that the area was in atypical shallow water delta environment when the third member of Shaliugang Formation was deposited,with its material source provenance from Qixi uplift.On the whole,the area should belong to the traction current deposit characterized by near source,poor sorting,frequent facies change and strong block partition and the sedimentary microp facies is dominated by underwater distributary channels.The spatial distribution of the sedimentary body is mainly controlled by the 6 NE-SE normal faults developed in the sedimentary period of the third member of Liushagang Formation.Faulting intensity difference controls the gully-gully geomorphology characteristics,distribution of source water system and provenance forward distance in this region,leading to the obvious difference of the various distribution channels.The gullies controlled by the two faults(F₃ and F₄) are relatively flat and the underwater distribution channels are promoting relatively far.This is an important exploration direction in eastern Wushi Depression.