北部湾盆地乌石凹陷东区流三段沉积体系发育特征及控制因素分析

北部湾盆地是南海北部最主要的含油气盆地之一,其中乌石凹陷东区流三段是主要的油气勘探目的层。该地层受控于复杂断裂体系,因此,其沉积模式及沉积微相展布一直是制约该区油气勘探突破的关键。通过岩心-钻井-地震资料的综合研究,深入分析了该区断层活动性及其空间展布、沉积物源体系及其沉积微相空间展布特征等,继而探讨了构造-沉积相互制约关系。研究结果表明:流三段沉积时期该区为非典型浅水三角洲沉积环境,物源来自于企西隆起,总体表现为近物源、分选差、相变快、断块分隔性较强的牵引流沉积特征,沉积微相以水下分流河道沉积为主;沉积体的空间展布主要受控于流三段沉积时期发育的6条NE向、EW向正断裂,断裂活动强度差异控制了该区沟谷相间的古地貌特征、物源水系的分布及物源推进距离,导致浅水三角洲内各分支水道差异性明显;其中乌石F₃、F₄两条断裂控制的断沟地势平缓,水下分流河道推进较远,是该区勘探的重要方向之一。 

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.