北部湾盆地乌石凹陷东区始新统流三段水进型扇三角洲沉积特征

Sedimentary characteristics of transgressive fan delta of the 3rd Member of Eocene Liushagang Formation in eastern Wushi sag, Beibuwan Basin

北部湾盆地乌石凹陷东区流沙港组三段岩性相对复杂,沉积差异大,横向变化快,连通性差,深入研究流沙港组三段沉积物源和沉积特征对油气勘探开发具有一定的指导意义。在系统的岩心观察与精细描述基础上,结合测井、地震和分析化验资料,针对研究区流沙港组三段沉积物源、沉积相类型及展布特征展开研究。综合分析认为,流沙港组三段物源来自于北部高地势地区,发育相对近物源的水进型扇三角洲沉积,砂体厚度较大,相带窄,相变快,其中三角洲前缘可进一步划分为水下分流河道、河口坝、席状砂、分流间湾等4种沉积微相;在物源分析、井震约束的基础上,依据井震结合含砂率等值线,同时结合测井平面相、地震反射结构、地震构型信息等,综合绘制研究区沉积微相平面展布图,确定了研究区流沙港组三段"大前缘小平原"的沉积特征,并最终建立了该区扇三角洲沉积模式,为乌石凹陷东区流沙港组三段油气勘探开发和储量计算提供了借鉴。

The lithology of the3rd Member of Liushagang Formation in eastern Wushi sag of Beibuwan Basin is relatively complex,with significant differences in sedimentary characteristics,rapid lateral changes and poor connectivity.The study of sedimentsources and sedimentary facies is controversial,and the oil and gas exploration and reserves calculation have long been constrainedby sedimentary facies study and its distribution regularity.In this paper,based on the core observation and fine description,combined with the logging,seismic and analytical data,the authors analyzed the sedimentary facies type and distributioncharacteristics of the3rd Member of Liushagang Formation.It is concluded that the sediment sources of the3rd Member ofLiushagang Formation were from the high terrain in the north,and the transgressive fan delta was developed in this area,with largersandbody thickness,narrow sedimentary facies,and fast sedimentary facies changes.The delta front can be further divided into fourkinds of sedimentary microfacies,i.e.,underwater distributary channel,channel dam,sandy sand,and shunt bay.Based on the sand-containing contours compiled by the combination of well and seismic survey,combined with the logging plane facies,seismic faciesand seismic reflection structure,the sedimentary microfacies plane profile of the study area was drawn comprehensively,and thesedimentary characteristics of the3rd Member of Liushagang Formation in the study area were determined.Finally,the fan deltadeposition model in this area was established,which provides reference for oil and gas exploration and development and reservecalculation of the3rd Member of Liushagang Formation in easternWushi sag,Beibuwan Basin.