Abstract: The shale in deep water areas of a continental lacustrine basin represented by the Member 2 of Kongdian Formation of Cangdong sag in Bohai Bay Basin boasts good shale oil exploration and development potential. However, the relationship between macroscopic distribution of lithofacies and microscopic characteristics of reservoirs is still unclear. Based on high frequency transgressive-regressive (T-R) sequence division of shale, using the methods such as core observation description, rock thin section identification, quantitative analysis of minerals by X-ray diffraction, elemental and organic geochemical testing, logging curve, field emission scanning electron microscopy analysis, nitrogen adsorption experiment, high pressure mercury injection experiment, and focused ion beam scanning electron microscope analysis, this paper analyzes the lithofacies filling evolution of different types of sequences and reservoir characteristics of different lithofacies, and explores the effect of high frequency sequence on reservoir development. The research results show that organic-rich shale section of the Member 2 of Kongdian Formation in Cangdong sag can be divided into 11 high frequency T-R sequences (5th-order sequence SQ①-SQ⑪, of which SQ⑨ develops gravity flow sandstone). According to the symmetry of lacustrine T-R cycles in high-frequency sequences, the sequences can be divided into asymmetric type dominated by T cycle, asymmetric and nearly symmetric types dominated by R cycle. Shale reservoirs mainly develop micropores such as intergranular pores, intra-granular pores, organic matter pores, and microcracks, among which inorganic pores such as intergranular pores and intra-granular pores are the main ones. The lamellar felsic shale facies and lamellar hybrid shale facies with higher content of felsic minerals and more laminated structures develop more macropores with better connectivity, while the massive hybrid shale facies and lamellar/massive carbonate shale facies with higher carbonate mineral content and more massive structures develop mesopores with general connectivity. Affected by mineral content and sedimentary structure, the shale reservoirs demonstrate the obvious characteristic of being controlled by facies, and the high frequency sequence can be regarded as a response to the changes in sedimentary environment in continuous time series, thus influencing the sedimentation of shale in the center of lacustrine basin. The significantly different reservoir characteristics correspond to high-frequency sequences at different evolutionary stages. Specifically, the middle-upper sequence at the rapid lacustrine transgression stage and bottom sequence at the oscillating lacustrine transgression stage are the high quality reservoir development section, and only local sequences at the stable high stage develop high quality reservoirs. These results are expected to provide theoretical support for the division of high-frequency shale sequences in deep water areas of a continental lacustrine basin as well as evaluation and prediction of high-quality reservoirs.

Key words: high frequency T-R sequence, sequence type, sequence evolution, pore structure, Cangdong sag

摘要： 以渤海湾盆地沧东凹陷孔店组二段（孔二段）为代表的陆相湖盆深水区页岩具有良好的页岩油勘探开发潜力，但其岩相宏观分布与储层微观特征的联系尚不明确。利用岩心观察描述、岩石薄片鉴定、X射线衍射矿物定量分析、元素及有机地球化学测试、测井曲线、场发射扫描电镜分析、氮气吸附实验、高压压汞实验、聚焦离子束扫描电镜分析等方法，在页岩高频湖进-湖退（T-R）层序划分的基础上，分析了不同类型层序的岩相充填演化序列和不同岩相的储层特征，探讨了高频层序对储层发育的影响。研究结果表明：沧东凹陷孔二段富有机质页岩段可划分为11个高频T-R层序（五级层序SQ①—SQ⑪，其中，SQ⑨发育重力流成因砂岩）；根据高频层序内T-R旋回的对称性，层序可分为以T旋回为主的不对称型、以R旋回为主的不对称型和近对称型；页岩储层主要发育粒间孔、粒内孔、有机质孔和微裂缝等微观孔隙，以粒间孔和粒内孔等无机孔为主；长英质矿物含量更高、纹层状构造更发育的纹层状长英页岩相和纹层状混合页岩相的宏孔更为发育，连通性更好，而碳酸盐矿物含量更高、块状构造更发育的块状混合页岩相和纹层状/块状碳酸盐页岩相的介孔更为发育，连通性一般；页岩的储层特征受矿物含量和沉积构造影响，呈现出明显的"相控"特征，而高频层序可以看作是连续时间序列下沉积环境变化的响应，影响着湖盆中心页岩的沉积作用；高频层序在不同演化阶段的储层特征差异明显，快速湖侵阶段的中—上部层序和振荡湖侵阶段的底部层序为优质储层发育段，而在稳定高位阶段仅局部层序发育优质储层。研究成果以期为陆相湖盆深水区页岩高频层序的划分及优质储层评价与预测提供理论支撑。

关键词: 高频T-R层序, 层序类型, 层序演化, 孔隙结构, 沧东凹陷