S1 Data -

The Upper Cretaceous Qingshankou Formation’s lacustrine shales in the Songliao Basin are among China’s most promising shale oil reservoirs. To elucidate their pore and fractal characteristics, a comprehensive set of analyses encompassing total organic carbon (TOC), X-ray diffraction (XRD), and low-temperature N2 adsorption (LTNA), Rock-Eval pyrolysis experiments and two-dimensional nuclear magnetic resonance (2D-NMR) were conducted. Using the Frenkel-Halsey-Hill (FHH) method, fractal dimensions (D) were calculated, and their relationship with pore metrics and shale compositions were explored. Two distinct fractal dimensions, D1 (0 < P/P0 < 0.5) and D2 (0.5
0 <1.0), were derived from LTNA isotherms via the FHH approach. D1 values fluctuated between 2.5715 and 2.7551 (mean 2.6564), while D2 spanned from 2.3247 to 2.4209 (mean 2.3653). Notably, D1 consistently surpassed D2, signifying that smaller pores exhibit greater homogeneity compared to their larger counterparts. D1 gradually increases with the increase of clay content. A direct correlation was observed between pore volume (PV), specific surface area (SSA), and D (both D1 and D2), whereas the association between average pore diameter (APD) and D was inverse. Both D1 and D2 escalated with diminishing TOC, 2D-NMR solid organic matter (OM), S1 content and 2D-NMR light oil. Intriguingly, D1 showed a stronger association with key pore and "sweet spot" parameters, highlighting its utility in assessing pore structural complexity and shale oil potential. This study illustrates how fractal theory enhances our understanding of pore structures and the shale oil enrichment process for the lacustrine shale.

松辽盆地上白垩统青山口组湖相页岩是中国最具潜力的页岩油储层之一。为阐明其孔隙与分形特征，研究人员开展了涵盖总有机碳（total organic carbon, TOC）、X射线衍射（X-ray diffraction, XRD）、低温氮气吸附（low-temperature N₂ adsorption, LTNA）、Rock-Eval热解实验以及二维核磁共振（two-dimensional nuclear magnetic resonance, 2D-NMR）在内的一系列综合分析。采用弗伦克尔-哈尔西-希尔（Frenkel-Halsey-Hill, FHH）模型计算分形维数（D），并探究其与孔隙参数及页岩组分间的关联。通过FHH方法对低温氮气吸附等温线进行分析，得到两个不同的分形维数：D1（对应相对压力0 < P/P₀ < 0.5区间）与D2（对应0.5 < P/P₀ < 1.0区间）。D1的取值范围为2.5715~2.7551（平均值为2.6564），D2的取值范围为2.3247~2.4209（平均值为2.3653）。值得注意的是，D1始终大于D2，这表明相较于大孔隙，小孔隙具备更高的均一性。D1随黏土含量的增加而逐渐升高。孔隙体积（pore volume, PV）、比表面积（specific surface area, SSA）与分形维数（D1和D2）均呈现正相关关系，而平均孔径（average pore diameter, APD）与分形维数则呈负相关。此外，D1和D2均随总有机碳含量、二维核磁共振固态有机质（OM）、热解S1峰含量以及二维核磁共振轻质油含量的降低而升高。有趣的是，D1与关键孔隙参数及“甜点区”参数的相关性更强，这凸显了其在评估孔隙结构复杂性与页岩油勘探潜力中的应用价值。本研究阐明了分形理论如何加深我们对湖相页岩孔隙结构及页岩油富集过程的认识。