渤海湾盆地沾化凹陷沙河街组三段下亚段细粒沉积岩岩相特征与沉积演化

渤海湾盆地沾化凹陷沙河街组三段（沙三段）下亚段页岩油勘探潜力巨大，目前对其岩相类型及其分布规律、沉积背景认识不清，制约了页岩油的勘探突破。利用岩心和X射线衍射、元素地球化学、有机地球化学等高精度测试资料，通过识别细粒沉积岩的岩相类型，恢复了古沉积环境，并探讨了沉积环境演变约束下的岩相分布规律。沉积古环境的变化控制了不同岩相类型的垂向分布及演化。沾化凹陷沙三段下亚段沉积环境自下而上划分为5个演化阶段，分别发育沉积藻灰岩、纹层状泥灰岩、纹层状重结晶灰岩、纹层状灰质泥岩和块状灰质泥岩。阶段Ⅰ—阶段Ⅲ，古气候相对干旱，陆源输入作用弱，沉积物以湖盆自生的灰岩为主，湖盆水体深度和盐度的变化控制了不同灰岩的变化；阶段Ⅳ，古气候转为湿热，陆源输入作用增强，沉积了陆源成因具年纹层构造的纹层状灰质泥岩；阶段Ⅴ，古气候最为湿热，陆源输入作用最强，发育大量浊流成因的块状灰质泥岩。垂向上，纹层状灰质泥岩的TOC含量最高、含油性最好。研究认识可为进一步厘清沾化凹陷沙三段细粒沉积岩储层非均质性的形成机制和页岩油甜点预测提供理论支撑。

Lithofacies and depositional evolution of fine-grained sedimentary rocks in the lower submember of the Member 3 of Shahejie Formation in Zhanhua sag,Bohai Bay Basin

Shale oil in the lower submember of the Member 3 of Shahejie Formation in Zhanhua sag of Bohai Bay Basin has huge exploration potential. At present, there is less understanding of its lithofacies type, distribution law, and sedimentary background, which restricts the breakthrough in shale oil exploration in this area. Using high-precision test data such as core and X-ray diffraction, elementary geochemistry, organic geochemistry, this paper identifies the lithofacies types of fine-grained sedimentary rocks, restores the sedimentary environment, and explores the distribution law of lithofacies in the evolution process of depositional environment. The vertical distribution and evolution of different lithofacies types is controlled by changes in the sedimentary environment. The evolution of the sedimentary environment of the lower submember of Member 3 of Shahejie Formation in Zhanhua sag is divided into five stages from bottom to top, with the deposition of algal limestone, laminar marlstone, laminar sparite, laminar lime mudstone and massive lime mudstone, respectively. In the stages Ⅰ to stage Ⅲ, the climate was relatively arid, the terrestrial input was weak, authigenic limestone deposits in the lake basin was mainly developed; changes in the water depth and salinity of the lake basin controlled the variations in different limestone lithofacies. In the stage Ⅳ, the climate became hot and humid, the terrestrial input was enhanced, and the laminar lime mudstone originated from terrigenous annual layers was deposited. In the stage Ⅴ, the climate was the hottest and dampest, when the terrestrial input was strongest, and a large number of massive lime mudstones formed by turbidity current were developed. Vertically, the laminar lime mudstone has the highest TOC content and the optimal oiliness. The research results can provide a theoretical support for further clarifying the difference mechanism of the heterogeneity of fine-grained sedimentary rock reservoirs, and predicting the sweet spots of shale oil in the study area.