湖泊滨岸砂坝内部结构特征剖析及其地质意义--以峡山湖现代砂坝沉积为例

湖泊滨岸砂坝通常会形成优质储集体，是近年油气勘探开发的重点目标之一。然而，对砂坝内部结构特征认识不清，制约了油田的进一步开发和剩余油挖潜。位于山东省中部的峡山湖，其东南岸发育多列沿岸分布的现代砂坝沉积，以此为例，利用浅钻孔、探坑等手段对砂坝内部结构进行细致剖析。研究表明，砂坝总体呈现下细上粗的反粒序结构，其内部由一个或多个增生体叠加而成，增生体之间界面处通常发育泥质沉积（落淤层）。增生体在砂坝内部主要有覆盖式和顶积式2种堆积样式，前者加积作用强，保存较好，增生体规模向上逐渐变大；后者加积作用弱，增生体易受波浪冲刷破坏，规模向上减小。砂坝内落淤层的分布与增生堆积样式有关，覆盖式增生体间的落淤层呈连片披覆状，向湖盆中心倾斜型分布；顶积式增生体间的落淤层呈孤立残留状，近水平零星散布在增生体界面处。现代砂坝内部结构的解剖结果不仅可为认识砂坝储层中砂体的堆积样式和砂、泥岩的空间配置关系提供真实的原型地质模式指导，在建立砂坝储层地质模型时还可提供定量化的条件约束。

Anatomy of Architecture Characteristics in Lacustrine Sand Banks and Its Geological Implications: A case study of modern sand banks in Xiashan Lake

The lacustrine near-shore sand bank is one type of good reservoirs, being the key target for oil and gas exploration and development recently. However, lacking clearly understanding of the inner architecture in this type of reservoir significantly restricts the further reservoir development. In southeastern Xiashan Lake, located in the center of Shandong Province, there are a series of modern sand banks observed parallelly to the lake shoreline. By using shallow wells, pits and other methods, a comprehensive research has been conducted to analyze the inner architecture of sand banks. The result shows that a sand bank has a general coarsening upward structure and is made up of one or more accretions. Between two accretions a thin layer of mud deposition can be found. There are two kinds of accretion stack patterns in a single sand bank which are one overlay pattern and one top-set pattern. The former pattern can usually be well persevered and presents a gradually expanding accretion from bottom to top due to strong aggradation. The latter pattern is easily destructed by flush erosion of wave actions and presents a gradually reducing accretion from bottom to top due to weak aggradation. The distribution of mud layer between two accretions is also determined by accretion stack patterns. The mud layer within an overlay pattern displays a continuous draping shape inclining to the lake center, while the mud layers, within a top-set pattern are isolated and discrete which are parallel to the interface of two accretions. A clear understanding of inner architecture in modern sand banks not only provides a real prototype model for better understanding in accretion stack patterns and spatial distribution of sand bodies in sand banks, but also offers quantitative constraints for 3D sand bank geological modeling.