Abstract: Lamellar calcite veins are widely developed in the lacustrine dark fine-grained sedimentary rocks from the upper submember of Member 4 to the lower submember of Member 3 of Shahejie Formation in Niuzhuang subsag. The distribution of these veins is characterized by strong heterogeneity, which is of great significance for the development of shale oil sweet spots. The research shows that the development of lamellar calcite veins is controlled by the lithofacies of fine-grained sedimentary rocks, which are mainly developed in organic-rich lamellar calcareous mudstones and argillaceous limestones. In fine-grained sedimentary rocks, the well-developed lamellar structure and the lithofacies type with the TOC content of more than 2%, carbonate content of 10%-70%, and argillaceous content of greater than 20% are favorable for the development of calcite veins. Among them, TOC content plays a more significant role in controlling the development of lamellar calcite veins. The lamellar bright calcite veins were mainly formed in the semi-mature and mature stage of organic matters. The carbonate minerals precipitated in the early stage of fine-grained sedimentary rocks serve as the main material source for veins formation. These minerals dissolve under the action of organic acids and enter the vein-forming fluids formed by hydrocarbon generation and clay mineral transformation. Under the effect of hydrocarbon generation pressure, horizontal microfractures are formed along the laminas of fine-grained sedimentary rocks, and vein-forming fluids migrate along this channel and recrystallize in the surrounding pressure relief area to form lamellar bright calcite veins. Research shows that only the fine-grained sedimentary rocks corresponding to the evolution depth of source rocks, which can provide sufficient vein-forming materials and fluids and have rich laminated structure, are easy to develop calcite veins in Niuzhuang subsag. Based on this, the development model of calcite veins has been established.

Key words: fine-grained sedimentary rock, shale oil, calcite vein, development mechanism, Niuzhuang subsag

摘要： 纹层状亮晶方解石脉广泛发育于东营凹陷牛庄洼陷古近系沙河街组四段（沙四段）上亚段—沙河街组三段（沙三段）下亚段的湖相暗色细粒沉积岩中，其分布具有较强的非均质性，对于页岩油甜点的发育具有重要意义。研究发现，纹层状方解石脉的发育受细粒沉积岩岩相控制，主要形成于富有机质纹层状钙质泥岩、泥质灰岩中。在细粒沉积岩中，纹层状构造发育且总有机碳（TOC）含量＞2%、碳酸盐含量为10%~70%、泥质含量＞20%的岩相类型有利于纹层状方解石脉发育；其中，TOC含量对方解石脉发育的控制作用更为明显。纹层状亮晶方解石脉的形成时期主要在有机质半成熟—成熟阶段，细粒沉积岩早期沉淀的碳酸盐矿物作为脉体形成的主要物质来源，在有机酸作用下发生溶解，进入由生烃作用和黏土矿物转化形成的成脉流体中；在生烃压力的作用下，沿细粒沉积岩纹层形成水平微裂缝，成脉流体沿此通道运移并在周边泄压区重结晶形成纹层状亮晶方解石脉。研究表明，在牛庄洼陷，只有与烃源岩演化深度对应、能提供充足成脉物质和流体且富纹层构造的细粒沉积岩才容易发育方解石脉，据此建立了纹层状亮晶方解石脉的发育模式。

关键词: 细粒沉积岩, 页岩油, 方解石脉, 发育机理, 牛庄洼陷