鄂尔多斯盆地延长组泥页岩硅质来源与油气富集

摘要

为了弄清鄂尔多斯盆地上三叠统延长组长7段和长9段泥页岩硅质来源与油气富集上的差异性,进行了主微量元素分析、全岩黏土X衍射、岩石热解、有机碳分析和扫描电镜观察研究.延长组泥页岩中长72亚段和长9段在硅质来源、矿物组成、元素组成和有机地化特征方面表现出更多相似之处,而长73亚段泥页岩与前面2套泥页岩则表现出一定的差异性.长72亚段和长9段泥页岩中的硅质主要来自于陆源碎屑物质,而长73亚段泥页岩硅质则表现出2种来源特征,即陆源碎屑来源和湖底热液喷流.延长组长7段和长9段泥页岩均是非常优质的烃源岩.但相比之下,受湖底热液作用的影响,长73亚段泥页岩残留烃和干酪根含量更高,干酪根类型也更好,页岩油饱和度指数更高.因此,长73亚段要优于长72亚段和长9段泥页岩,具有更高的开采价值.%A series of analyses, including major and trace element analysis, X-ray diffraction for bulk and clay mineral composition, Rock-Eval analysis, TOC analysis and scanning electron microscope observation, were conducted in order to determine the different silica sources and hydrocarbon accumulation between the Chang 7 member and Chang 9 member shale of the Triassic Yanchang Formation in the Ordos Basin. The Chang 72 sub-member and the Chang 9 member shale had more similarities in silica sources, mineral composition, element composition and organic geochemical characteristics, while the Chang 73 sub-member shale showed certain differences in the above properties from the other two sets of shale reservoirs. The silica in the Chang 72 sub-member and the Chang 9 member shale came from terrestrial detritus, while the silica in the Chang 73 sub-member shale showed the characteristics of two sources, namely, terrestrial detritus and hydrothermal from vents at the bottom of the lake. Both Chang 7 and Chang 9 shales are high-quality source rocks. However the contents of residual hydrocarbon and kerogen are higher, the type of kerogen is much better, and the oil saturation index is higher under the influence of hydrothermal fluid for the Chang 73 sub-member shale. Hence the Chang 73 sub-member is superior to the Chang 72 sub-member and Chang 9 member shale and has higher exploitation value.