Investigation of pore structures and flow transport characteristics of continental shale in Dongying Sag

Multiscale pore-slit structures, non-linear flow and complex lithofacies of continental shale in Dongying Sag present significant challenges for reservoir evaluation and sweet spots identification. This study establishes a comprehensive analytical framework through integrated physical experiments and high-resolution imaging to characterize pore-slit structures and flow dynamics across various lithofacies. Firstly, a novel PSD (pore size distribution) splicing technique is developed by combining multiscale feature extraction and a transformed method, seamlessly uniting nitrogen adsorption data with SEM (scanning electron microscopy) image analysis. Compared with traditional methods, this advanced technique provides a more comprehensive representation of shale pore size distribution and structural characteristics. Three permeability indexes, including the non-Darcy index (Knon−D), anisotropy index (Ka), and slit index (Kf), are proposed to quantify flow behavior based on the cubic-block and matrix permeability experiments. These innovative indexes allow us to explore the complex non-linear flow behaviors, the anisotropic flow properties and pore-slit crossflow characteristics of shale. Comparative analysis reveals distinct pore structure and flow characteristics among different lithofacies: clay-rich shale exhibits high porosity and matrix permeability, while carbonate-rich shale demonstrates stronger nonlinear flow capacity and anisotropic permeability. Finally, the intrinsic relationship between mineral composition, pore structure, and complex flow has been investigated, and the identification charts for porosity and permeability have been established. These findings provide valuable tools for enhanced reservoir evaluation and sweet spot identification in the continental shale formations of Dongying Sag.