Laminated Shale nm–µm‐Scale Pore System Structure, Fractal Dimensions and Its Controlling Factors of the Paleocene Shahejie Formation: Evidences From CO 2 Adsorption and N 2 Adsorption Experiments

ABSTRACT Characterizing the pore system of shale oil reservoirs is critical to elucidating petroleum accumulation mechanisms, enhancing oil recovery efficiency, and evaluating unconventional petroleum resources. However, research on lacustrine laminated shale pore systems remains limited and poorly understood, primarily constrained by the strong heterogeneity induced by differential lamina development. To address this gap, we collected 20 lacustrine shale samples from the fourth member of the Shahejie Formation in the Bohai Bay Basin and systematically investigated their nm–µm scale pore structure using CO 2 and N 2 adsorption experiments. The results show that the laminated shales are composed of light‐colored mineral‐rich layers (quartz, feldspar, calcite, and dolomite) alternating with dark clay–organic matter layers. Their pore system is dominated by matrix intercrystalline, intergranular, dissolution pores, and microfractures, rather than organic‐matter‐associated pores, with pore diameters primarily ranging from 2 to 40 nm. Notably, mesopores account for over half of the total specific surface area and pore volume in all tested samples, and the abundance of clay and quartz minerals is identified as the key factor controlling micro–mesopore composition and complexity. These findings provide critical insights for understanding shale oil resource potential and delineating optimal exploitation targets in lacustrine basins.