Abstract: This study aims to address the insufficient analysis and evaluation of the pore-throat structure in the shale reservoir of the first member of the Paleogene Shahejie Formation in Nanpu Depression.To achieve this,we utilized scanning electron microscopy(SEM),constant-rate mercury injection experiments,and fractal theory to evaluate the fractal dimension of pore-throats at different scales.The findings indicate that the pore throats in shale can be classified into two distinct types:large-scale and small-scale.Furthermore,the fractal dimensions of the pore throats vary significantly across different scales.The small-scale pore throats exhibit strong compaction and cementation,primarily consisting of intercrystalline pores,intragranular pores,and tubular throats.The degree of heterogeneity is low,and the deformation of pore throat space is minimal,resulting in a smaller fractal dimension.The predominant types of large-scale pore throats in shale reservoirs are intergranular pores,pore-shrinking throats,and curved throats.These pore throats exhibit significant reservoir space and deformation phenomena.The pore structure in shale reservoirs is highly heterogeneous,with a large fractal dimension.The presence of various types and sizes of pore throats in shale reservoirs results in distinct heterogeneity characteristics in the pore structure.The fractal dimension is an effective measure of the complexity of the reservoir pore structure.The research findings offer a crucial scientific foundation for the exploration and development of shale oil reservoirs,which is beneficial in enhancing the efficiency of shale oil development and holds significant importance for the later development of oil fields.

Key words: Nanpu Depression, Linque Sub-sag, Shahejie Formation, pore throat structure, fractal dimension, constant rate mercury penetration, shale