The mineral composition and diagenesis of shale play important roles in constraining the sealing efficiency as caprock of CO2 sequestration and the fracability in shale gas. X-ray fluorescence spectrum, X-ray diffraction and scanning electron microscopy are employed in the determination of mineral composition of mudstone and the identification of submicron-sized authigenic quartz crystals in well HX, Qingshankou Formation, Upper Cretaceous. The type of host rock and weathering effect are in consistent with mudstone in Qingshankou Formation. The mudstone is composed of clay mineral, albite, quartz and less K-feldspar. The clay fraction consists mainly of mixed-layer I/S and minor amounts of chlorite. Brittle mineral (albite, quartz and feldspar) average content is 44. 43%, and clay mineral content is 54. 26% on average. Submicron-sized authigenic quartz crystals released from S - I relation occur as large amounts of extremely fine-grained micro-sized crystals embedded as discrete,small clustersest and locate in micropores in mixed-layer I/S. The caprock consisting of mainly mixed-layer I/S mineral and minor amount of micron-quartz will be conductive to long-term CO2 geological storage. The content of brittle mineral meet the reservoir standard of industrial value shale gas, while the content of clay mineral is quite low.%泥质岩的矿物组成和成岩作用是制约其作为CO2地质封存的盖层封闭能力和作为页岩气储层具易压裂性质的重要原因.通过地球化学分析、X-射线衍射分析和扫描电镜观测及能谱测定,确定了松辽盆地南部HX井上白垩统青山口组泥岩的矿物组成.识别出了蒙皂石转变伊利石反应过程中形成的亚微米级自生微晶石英.研究表明:HX井上白垩统青山口组泥岩的母岩岩石类型和风化效应一致,泥岩主要由黏土矿物、钠长石和石英组成,钾长石少量；黏土矿物以伊利石/蒙皂石混层为主,其次为绿泥石；脆性矿物(钠长石、石英和钾长石)的平均质量分数为44.43％,黏土矿物平均质量分数为54.26％.蒙皂石转变伊利石反应过程中形成的亚微米级微晶石英单晶呈自形—半自形粒状,集合体呈巢状,分布于伊利石/蒙皂石混层黏土矿物的微孔隙中.以伊利石/蒙皂石混层矿物为主、且存在一定量的自生微晶石英的泥岩盖层(例如HX井青山口组泥岩)将有助于注入CO2的长期封存.HX井青山口组泥岩中的脆性矿物含量符合工业价值页岩气的储层标准,而黏土矿物含量则相差较多.
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