School of Geography, South China Normal University, Guangzhou 510631, China.
State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
J Nanosci Nanotechnol. 2021 Jan 1;21(1):646-658. doi: 10.1166/jnn.2021.18475.
Shale gas has been playing an increasingly important role in meeting global energy demands. The heterogeneity of the pore structure in organic-rich shales greatly affects the adsorption, desorption, diffusion and flow of gas. The pore size distribution (PSD) is a key parameter of the heterogeneity of the shale pore structure. In this study, the Neimark-Kiselev (N-K) fractal approach was applied to investigate the heterogeneity in the PSD of the lower Silurian organic-rich shales in South China using low-pressure N₂ adsorption, total organic carbon (TOC) content, maturity analysis, X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) measurements. The results show that (1) the fractal dimension obtained by N-K theory better represents the heterogeneity of the PSD in shale at an approximately 1-100 nm scale. The values range from 2.3801 to 2.9915, with a mean of 2.753. The stronger the PSD heterogeneity is, the higher the value in shale is. (2) The clay-rich samples display multimodal patterns at pore sizes greater than 20 nm, which strongly effect the PSD heterogeneity. Quartz-rich samples display major peaks at less than or equal to a 10 nm pore size, with a smaller effect on the PSD heterogeneity in most cases. In other brittle mineral-rich samples, there are no obvious major peaks, and a weak heterogeneity of the PSDs is displayed. (3) A greater TOC content, maturity, clay content and pore size can cause stronger heterogeneity of the PSD and higher fractal dimensions in the shale samples. This study helps to understand and compare the PSD and fractal characteristics from different samples and provides important theoretical guidance and a scientific basis for the exploration and development of shale gas resources.
页岩气在满足全球能源需求方面发挥着越来越重要的作用。富有机质页岩中孔隙结构的非均质性极大地影响了气体的吸附、解吸、扩散和流动。孔径分布（PSD）是页岩孔隙结构非均质性的关键参数。本研究采用 Neimark-Kiselev（N-K）分形方法，利用低压 N₂吸附、总有机碳（TOC）含量、成熟度分析、X 射线衍射（XRD）和场发射扫描电子显微镜（FE-SEM）测量，研究了中国南方下志留统富有机质页岩 PSD 的非均质性。结果表明：（1）N-K 理论得到的分形维数 更好地代表了页岩在 1-100nm 尺度上的 PSD 非均质性。 值范围为 2.3801-2.9915，平均值为 2.753。页岩 PSD 非均质性越强， 值越高。（2）粘土含量高的样品在大于 20nm 的孔径处表现出多峰模式，强烈影响 PSD 非均质性。石英含量高的样品在小于或等于 10nm 的孔径处显示主要峰，在大多数情况下对 PSD 非均质性的影响较小。在其他脆性矿物含量高的样品中，没有明显的主峰，显示出较弱的 PSD 非均质性。（3）TOC 含量、成熟度、粘土含量和孔径越大，页岩样品的 PSD 非均质性越强，分形维数越高。本研究有助于理解和比较不同样品的 PSD 和分形特征，为页岩气资源的勘探和开发提供了重要的理论指导和科学依据。
