Pore Structure Characterization of Lacustrine Shale and its Coupling Relationship with Sedimentary Structure from the Upper Cretaceous Qingshankou Formation, Southern Songliao Basin, NE China

Characterizing the microscopic pore systems in shale reservoirs is crucial for understanding their impact on shale oil and gas enrichment. Although significant strides have been made in understanding the pore structure characteristics, research on pore structures related to small-scale sedimentary structures remains limited. This study investigated the multi-scale nanopore structure characterization and its coupling relationship with sedimentary structures using comprehensive analyses of cores, field-emission scanning electron microscopy, and gas (CO2 and N2) physisorption quantification from the Upper Cretaceous Qingshankou Formation, Southern Songliao Basin, NE China. Three lithofacies were identified based on sedimentary structures: wavy laminated shale, horizontally laminated shale, and homogeneously laminated shale. Both organic and inorganic pores (interparticle pores and intraparticle pores) are generally present in shale samples. The pore size distribution displays a multi-peak pattern, with mesopores contributing to approximately 57% of the total pore volume, micropores contributing to about 31%, and macropores accounting for a small portion of the total pore volume. The pore evolution of different lithofacies shales varies due to the influence of clay minerals, quartz content, and total organic carbon (TOC) content, resulting in the substantial heterogeneity and complex pore structure characteristics of existing reservoirs. Additionally, wavy laminated shales are more favorable to lacustrine shale exploration than other lithofacies. This study offers an enhanced methodology for determining which lithofacies may be most advantageous for future shale oil exploitation.