热异常酸洗作用与鄂尔多斯盆地上古生界长石消失事件

Pickling Effect of the Abnormal Heat and Its Relation to Disappearance of Feldspar of the Upper Paleozoic in the Ordos Basin

鄂尔多斯盆地上古生界煤系砂岩储层普遍具有低长石、溶蚀孔隙发育的特点,通过大量岩石薄片鉴定、X-射线衍射、扫描电镜、地层条件下高温高压真实砂岩岩芯的酸溶溶蚀实验等手段,结合鄂尔多斯盆地的构造、热演化史分析,研究了上古生界煤系地层中长石大面积消失事件的机理。认为早白垩世"热异常酸性流体酸洗地层事件"导致上古生界煤系地层中长石大面积溶蚀消失,形成广泛分布的次生溶蚀孔隙发育带,长石的分布与埋深无关,热演化程度的差异直接控制长石的消亡与否。据此,建立了鄂尔多斯盆地上古生界煤系地层成岩演化及长石溶蚀消失次生溶孔发育模式。

Sandstone reservoir in the Upper Paleozoic coal-bearing strata of the Ordos basin is generally characterized by low feldspar content and well-developed dissolution pores.Combining with structure background of the Ordos basin and the thermal evolution history,we studied mechanism from which a large amount of feldspar disappeared in Upper Paleozoic coal-bearing strata using thin section identification,X-ray diffraction,scanning electron microscopy（SEM）,geological conditions（high temperature and high pressure）of sandstone acid dissolution experiment.It can be concluded that pickling effect of the abnormal heat during Early Cretaceous resulted in disappearance of large volume of feldspar in the Upper Paleozoic coal-bearing strata,giving a rise to the formation of widely distributed secondary dissolution pores.The distribution of feldspar has nothing to do with buried depth,and difference of thermal evolution degree controlled directly the disappearance of feldspar.Based on the research above,this study established the model of diagenetic evolution of the Upper Paleozoic coal-bearing strata and secondary solution pore development in the Ordos Basin after completion of feldspar dissolution.