涠西南凹陷A井区古近系流沙港组一段砂体沉积特征及分布规律

涠西南凹陷A井区古近系流沙港组一段下亚段发育了大规模的砂砾岩沉积。岩芯观察及分析化验资料表明砂砾岩沉积发育丰富的能够反映浊流沉积的鲍马序列、冲刷充填及变形构造等沉积构造并具有直线一段式和上拱一段式等粒度概率曲线类型。垂向以多个底部发育冲刷充填构造的正旋回叠加为特征,整体表现为正序。沉积特征表明砂砾岩为湖底扇沉积。综合利用地震反射特征及垂向地层叠加样式等方法,在流一段湖底扇内共识别出3个五级层序,将湖底扇沉积划分为3期。各旋回湖底扇砂体厚度与平均波峰振幅、能量半时及瞬时频率等地震属性有良好的相关关系。在高精度层序地层格架的约束下,结合钻井及录井资料分析与地震属性分析,对3期湖底扇砂体平面分布特征进行了研究,各期湖底扇具有左右迁移摆动、垂向叠置发育的特征。由于受到3号控盆断层和0号隐伏断层的影响,使得涠西南低突起北缘发育的5号断层幕式活动,导致研究区可容空间发生转换,构造运动控制的可容空间不均衡转换是控制流一段湖底扇砂体分布规律的主要因素。

Sedimentary Characteristics and Distribution Law of Sandbodies of the First Member of Liushagang Formation of Paleogene of A Well Field in Weixinan Depression

 Large scale glutenite was developed in the sedimentary period of the lower submember of first Member of Liushagang Formation of Paleogene in A well field of Weixinan Depression. Core and analysis and test data l suggest that the sandbody developed abundant sedimentary structure of Bouma cycle, erosion and loading, and the deformation structure and has the type of grain size accumulation curve of uphill arched "1 segment" pattern and line "1 segment" pattern. In vertical section, characterized by superposition of several positive cycles with the sedimentary structure of erosion and loading in the bottom, phase sequence displays the positive sequence as a whole. Sedimentary characteristics showed that the glutenite was sublacustrine fan. 3 stages of sublacustrine fan deposits have been recognized according to the seismic reflection characteristics and the patterns of superposition of verstical formation. In each stage the thickness of sand body of sublacustrine fan is well related to the seismic attribution of average peak amplitude, energy half time and instantaneous frequency. Under the constraint of high resolution sequence stratigraphic framework, combined with well drilling, logging and analysis of seismic attribution, each stage of sublacustrine fan is characterized by contstant migration and wiggle in two dimensional system, and superimposed development in the vertical evolution. The episodic activity of No.5 fault as a result of the influence of No. 0 fault and No.3 fault, led to the transformation of accommatation space. So, the unbalanced transformation of accommatation space constrainted by structure activity is the main factor controlling the distribution of sand body of sublacustrine fan of the first Member of Liushagang Formation.