Abnormally high-porosity zones in deep reservoirs are widely developed in the fourth member of the Eocene Shahejie Formation (Es4) in the fault-step zone of the Bonan Sag, Jiyang Depression, Bohai Bay Basin, China. However, research on reservoir diversity in these abnormally high-porosity zones has focused on the shallow parts of the reservoirs, and their genetic mechanisms remain unclear, restricting further exploration and development. In this study, comprehensive experimental analysis methods, including casting thin-section observation, scanning electron microscopy and digital core analysis were used to quantitatively characterise the pore structure of the different types of reservoirs in the Es4 abnormally high-porosity zone and analyse the genetic mechanism of these relatively high-quality reservoirs. The results indicate great reservoir diversity in the Es4 abnormally high-porosity zone. The main reservoir rocks are fine-to-coarse feldspar lithic or lithic feldspar sandstone with low porosity and low permeability and can be subdivided into three types (A–C). Four three-dimensional pore-structure models were constructed via the Avizo software to quantitatively reveal the reservoir diversity. The results suggest that ‘macropores’ and ‘mesopores’ are the most significant contributors to both the total pore volume and the amount of connected pores. Many ‘macropores’ and ‘mesopores’ are connected by many pore throats in Type A reservoirs, but these are significantly reduced in Type B reservoirs. Type C reservoirs hardly contain any (connected) ‘macropores’ and ‘mesopores’. Comprehensive analyses of the reservoir physical properties, secondary mineral composition and pore structure demonstrate that primary sedimentary conditions, calcite cementation and dissolution are the main factors that determine reservoir diversity in the Es4 abnormally high-porosity zone. Strong dissolution and effective removal of secondary products are the main mechanisms of the formation of Type A reservoirs, whereas strong dissolution failing to remove dissolution products has led to the formation of Type B reservoirs. Primary sedimentary conditions, strong calcite cementation and lack of dissolution are the main causes of failure to form effective pore networks in Type C reservoirs.

在渤海湾盆地济阳De陷博南凹陷断陷阶跃区的始新统沙四段（Es4）第四段，深层储层中异常高孔隙度地区得到了广泛开发。但是，这些异常高孔隙度地区的储层多样性研究集中在浅层储层，其成因机制尚不清楚，限制了进一步的勘探和开发。在这项研究中，综合的实验分析方法，包括铸件薄层观察，扫描电子显微镜和数字岩心分析，被用来定量表征Es4异常高孔隙度地区不同类型储层的孔隙结构并分析其成因。这些相对优质的水库中。结果表明，在Es4异常高孔隙度地区储层多样性很大。主要的储集岩为孔隙度低，渗透率低的细至粗长石岩质或长石岩质砂岩，可细分为三种类型（AC）。通过Avizo软件构建了四个三维孔隙结构模型，定量地揭示了储层的多样性。结果表明，“大孔”和“中孔”是总孔体积和连通孔数量的最重要贡献者。在A型储层中，许多“大孔”和“中孔”通过许多孔喉相连，但在B型储层中则明显减少。C型储层几乎不包含任何（连通的）“大孔”和“中孔”。综合分析储层物性 次生矿物组成和孔隙结构表明，主要沉积条件，方解石胶结作用和溶解作用是决定Es4异常高孔隙度地区储层多样性的主要因素。强烈溶解和有效去除副产物是形成A型储层的主要机制，而强烈溶解却未能去除溶解产物导致了B型储层的形成。主要的沉积条件，强方解石胶结作用和缺乏溶解是造成C型储层未能形成有效孔隙网络的主要原因。强溶解和有效去除副产物是形成A型储层的主要机制，而强溶解却未能去除溶解产物导致B型储层的形成。主要的沉积条件，强方解石胶结作用和缺乏溶解是造成C型储层未能形成有效孔隙网络的主要原因。强溶解和有效去除副产物是形成A型储层的主要机制，而强溶解却未能去除溶解产物导致B型储层的形成。主要的沉积条件，强方解石胶结作用和缺乏溶解是造成C型储层未能形成有效孔隙网络的主要原因。