南海南部南安盆地新生代以来构造-沉积演化特征及区域成藏模式

The tectono-sedimentary evolution characteristics and regional reservoir-forming model of Nan’an Basin in the Cenozoic

  • 摘要: 南安盆地是南海南部重要的大型含油气盆地之一,深入分析其构造-沉积演化特征对盆地油气勘探具有重要的指导作用。结合已有研究成果,开展盆地二维地震资料解释,识别出南安盆地新生代以来5个主要的二级层序界面和4套地震层序。在层序地层格架下,根据地震反射特征识别出南安盆地楔形、S型(丘状)等5类地震相类型;砂包泥岩、砂泥岩互层等7类地震岩相类型以及扇三角洲、河流三角洲等8类主要沉积相。综合盆地构造演化特征,南安盆地新生代以来主要分为4个阶段:初始裂陷阶段、主裂陷阶段、断拗转换阶段和拗陷热沉降阶段。其中,中中新世以前为盆地裂陷阶段,发育陆源碎屑沉积,早期为湖相沉积,晚期为滨浅海相沉积;中中新世以后为拗陷阶段,发育陆源碎屑沉积和碳酸盐岩沉积。通过油气成藏模式研究,南安盆地烃源岩发育且品质较好,有利储集相带纵向厚度大且横向范围广,区域盖层覆盖整个盆地,并形成了早期的自生自储和晚期的下生上储两类油气成藏系统。

     

    Abstract: Nan’an Basin is one of the important large oil-gas basins in the southern South China Sea, and the in-depth analysis of its tectono-sedimentary evolution characteristics is of great significance for oil and gas exploration. Based on the existing research results, the 2D seismic data of the basin was interpreted, and five main second-order sequence interfaces and four sets of seismic sequences were identified in the basin in the Cenozoic. Based on the sequence stratigraphic framework, five types of seismic facies such as wedge-shaped and S-shaped (mound), seven seismic lithofacies types (such as sand-coated mudstone and interbedded sand-mudstone), and eight major sedimentary facies (such as fan delta and river delta) were identified. The tectonic evolution of the Cenozoic south basin was divided into four stages: initial rift stage, main rift stage, fault-depression transformation stage, and depression thermal subsidence stage. Before the Mid-Miocene was the main rift stage, during which terrigenous clastic deposits formed from early lacustrine deposition to later offshore deposition. After the Middle Miocene was the depression stage, during which terrigenous clastic deposits and carbonate deposits developed. The study of hydrocarbon accumulation model showed that, the source rocks in Nan’an Basin are well developed and of good quality, which favored the reservoir facies belt enlargement in a large longitudinal thickness and a wide lateral range. The regional cap rocks covered the whole basin, and two types of hydrocarbon accumulation systems were formed: self-generation and self-storage in the early stage, and lower-generation and upper-reservoir in the late stage.

     

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