煤系烃源岩与石英次生加大边的形成机理探讨:以鄂尔多斯盆地东部山西组为例

Formation Mechanism of Coal Source Rocks and Quartz Overgrowths:An Example of Shanxi Formation in Eastern Ordos Basin

借助有机酸热模拟、岩石薄片及阴极发光实验资料,分析了鄂尔多斯东部地区山西组煤系烃源岩与石英次生加大边的关系。研究表明:煤系烃源岩以Ⅲ型干酪根为主,在热演化生烃的过程中由于含氧基团逐步断裂产生了大量的有机酸;在酸性微孔隙环境下,石英砂岩及其岩屑石英砂岩中的火山喷出岩屑、长石等不稳定矿物易遭受溶蚀,形成的SiO2提供了石英次生加大的硅质来源,薄片及阴极发光下均可观察到石英发育多期次生加大,尤以二期次生加大为主;证实煤系烃源岩中的有机酸是导致石英发生多期次生加大的直接原因,最终形成致密砂岩。

Based on the thermal simulation of organic acid,rock section and cathodeluminescence,we analysed the relationship between the coal source rocks and the quartz overgrowths in the coal source rock of Shanxi Formation of the eastern Ordos Basin.The research results indicate that theⅢ-kerogen from oxygenic clusters collapsing can produce more organic acids in the thermal simulation.While in the acidic pore environment,the experiment of rock section and cathodeluminescence shows that a large amount of organic acid dissolved unstable minerals such as volcanic debris and feldspar from quartz sandstone and debris quartz sandstone and new SiO2 that occurred in precipitation provided the source of quartz overgrowths.Accordingly,the existence of organic acid can cause quartz overgrowths and finally tight sandstone formed.