东营凹陷中央背斜带沙三段砂岩石英次生加大边发育特征及其指示意义

Characteristics of Quartz Overgrowth in Sandstones from Es3 Interval Central Anticlinal Belt in Dongying Depression and Its Significance

石英次生加大是砂岩储层中常见且重要的成岩现象.本文通过对东营凹陷中央背斜带沙三段不同含油级别砂岩样品铸体薄片镜下观察、石英次生加大边宽度和含量的定量统计以及流体包裹体测温,分析了不同含油级别砂岩中石英次生加大边发育特征、期次和石英次生加大所需硅质的可能来源.砂岩样品中石英次生加大边最大宽度和加大边面积分布范围变化大,分别分布在4~90μm和2.50~39 927.80μm^2之间.砂岩中与油气充注有关的石英次生加大主要有两期,结合埋藏-温度史图,该两期石英次生加大边发育时间分别为距今15~6 Ma和4~0 Ma.钾长石溶蚀和沙三段砂泥岩层中黏土矿物的转化是研究区不同含油级别砂岩石英次生加大边发育的主要硅质来源.东营凹陷中央背斜带沙三段不同含油级别砂岩石英次生加大边发育具有相似性和差异性两种特征:(1)不同含油级别砂岩中石英次生加大边最大宽度和单颗粒石英次生加大边面积整体统计分布特征具有相似性;(2)石英次生加大边宽度和单颗粒石英加大边面积普遍存在差异性.砂岩孔渗性、含烃流体充注造成的酸性水介质环境和油水分布特征是造成沙三段不同含油级别砂岩石英次生加大边发育相似性和差异性的主要原因,该区砂岩中石英次生加大可作为含烃流体充注的成岩示踪标志.

Quartz overgrowth is a common and important cementation in sandstone reservoirs. On the basis of micro-observation on different oil saturation sandstone thin sections from the Es3 interval of the Central Anticlinal Belt in Dongying depression, the width and the content of quartz overgrowth were quantified and the temperature of fluid inclusions were measured. Then the characteristics of quartz overgrowth, the stage of quartz overgrowth and the possible source of silica required for quartz overgrowth were analyzed. The width and the content of quartz overgrowth vary significantly with a range 4-90 μm and 2.50-39 927.80μm^2, respectively. There are two main stages of secondary quartz overgrowth related to oil and gas filling in sandstone. Combined with burial-temperature histories, the two stages of quartz overgrowth are 15-6 Ma and 4-0 Ma, respectively. The dissolution of potash feldspar and the transformation of clay minerals in sandstone and mudstone layers of the Es3 interval are the main siliceous sources for the quartz overgrowth. The characteristics of quartz overgrowth in different oil saturation sandstone can be concluded into the similarity and difference:(1) The overall distribution of maximum width of quartz overgrowth and the area of each quartz overgrowth in different oil saturation sandstone are the same;(2) the width and the area of quartz overgrowth are generally different from each other. Porosity and permeability of sandstone, acidic water environment caused by hydrocarbonbearing fluid filling and oil-water distribution characteristics are the main reasons for the similarity and difference of quartz overgrowth in sandstones with different oil saturation. And the quartz overgrowth can be regarded as trace marker of hydrocarbonbearing fluid filling.