陆相页岩与泥岩特征对比及其意义——以鄂尔多斯盆地延长组7段为例

Comparative study on lacustrine shale and mudstone and its significance:A case from the 7^(th) member of Yanchang Formation in the Ordos Basin

鄂尔多斯盆地延长组7段富含大量页岩油,但由于对页岩与泥岩特征差异缺乏深入了解,阻碍了该层系页岩油的有效开发。为此,采用岩心观察、薄片鉴定等直接观察手段与XRD、Rock-Eval、TOC、氯仿沥青"A"抽提、主微量元素等实验相结合,对研究区长7段页岩和泥岩的岩石学、矿物学、有机地球化学与无机地球化学特征进行了深入研究。结果表明:长7段页岩的颜色较深,发育明显页理,切面光滑,而泥岩不具有纹层和页理,断口不整齐且切面粗糙;页岩的有机质以顺层富集为主,泥岩有机质以分散赋存为主;页岩的粘土矿物含量较高,泥岩的石英含量较高;页岩的TOC平均值为18.5%,约为泥岩的5倍,生烃潜量是泥岩的5~8倍;氯仿沥青"A"组分对比显示页岩含较多的芳烃,泥岩则含有较多的饱和烃;页岩沉积水体的盐度相对泥岩略低,且水深相对较浅。长7段页岩呈西北-东南走向分布,厚度主要为15~30 m,与泥岩呈互补式分布。页岩油"源内聚集"的特点使长7段的页岩油宏观分布受到页岩相控制。开展泥岩与页岩的对比研究,对准确预测富有机质页岩分布及指导页岩油气勘探具有重要意义。

The 7thmember of Yanchang Formation（Chang 7） in Ordos Basin is rich in shale oil resources. However,a poor understanding of the differences of characteristics between shale and mudstone has hindered the exploitation of shale oil. Various methods including direct observation of core and thin section and analyses of XRD,Rock-Eval,TOC,chloroform bitumen ＂A＂extraction as well as major and trace element analysis are used to study the sedimentological,mineralogical and geochemical characteristics of shale and mudstone in Chang 7 Member of Triassic Yanchang Formation in Ordos Basin,Northwest China. The results indicate that the shale shows darker color,obvious lamination and smooth surface,while the mudstone has grey color,no fissiles,and non-smooth cut surface. The organic matters in shale are mainly enriched along beddings,the organic matters in the mudstone are scattered. The clay content is high in the shale,while quartz content is relatively high in the mudstone. The average TOC of the shale（18. 5%） is more than 5 times that of the mudstone and the hydrocarbon generation potential in shale is 5 ~ 8 times that in mudstone. More aromatic hydrocarbons and less saturated hydrocarbon is contained in the component of chloroform bitumen ＂A＂of shale than that of mudstone.The shale was deposited in an environment with lightly lower paleosalinity and shallower paleo-water depth than that of the mudstone. The shales in Chang 7 strike NW-SE and have thickness in the range of 15-30 m. The macroscopic distribution of shale oil is controlled by shale facies,therefore the comparative study between shale and mudstone is of great significance for accurate prediction of organic-rich shale and guiding shale oil/gas exploration.