| 摘要: |
| 根据二维高分辨率扫描电镜（2D-SEM）图像孔隙灰度阈值提取页岩孔隙分布，采用分形理论计算孔隙形态和孔径分布分形维数，在此基础上分析孔径分布模型、步长及分辨率对页岩2D-SEM孔径分布影响，并与高压压汞（MICP）和低温氮气吸附-解吸（LNA/D）孔径分布对比。结果表明：2D-SEM孔隙提取结果能够定量表征页岩孔隙结构复杂性，孔隙形态分形维数越高，孔隙越复杂，孔径分布分形维数越高，孔径分布越复杂，微孔所占比例越高；连续型孔径分布模型能够准确表征页岩孔径分布，以1/2平均孔喉半径为步长提取的2D-SEM与MICP和LNA/D孔径分布吻合最好；2D-SEM孔径分布受分辨率和页岩非均质性双重影响，应选择代表页岩孔隙结构的高分辨率区域，或采用多张高分辨率SEM拼接图像提取孔径分布；2D-SEM图像能够精确定量表征页岩孔隙结构特征，为取心及制样困难的页岩孔隙结构研究提供了新方法。 |
| 关键词: 扫描电镜 分形维数 孔径分布 孔隙结构 页岩 |
| DOI：10.3969/j.issn.1673-5005.2018.02.003 |
| 分类号:TE122.2 |
| 基金项目:国家自然基金重点基金项目（41330313）；国家自然科学基金青年科学基金项目（41602131）；中央高校基本科研业务费专项（17CX06036，17CX02074，YCX2017002）；中国石化股份有限公司资助项目（P17027-3） |
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| Quantitative characterization of microscopic pore structure for shales using scanning electron microscopy |
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ZHANG Pengfei, LU Shuangfang, LI Junqian, XUE Haitao, LI Wenbiao, WANG Siyuan1,2
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1. Research Institute of Unconventional Oil & Gas and Renewable Energy in China University of Petroleum, Qingdao 266580, China;2. School of Geosciences in China University of Petroleum, Qingdao 266580, China
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| Abstract: |
| The pore distribution of shales was extracted using the pores gray-level thresholds of the 2-dimensional high resolution scanning electron microscopy (2D-SEM) images. The fractal dimension of pore morphology and radius were calculated using the fractal theory. The impacts of pore size distribution (PSD) model, radial step increase and resolution on the PSD determined by 2D-SEM were investigated, and the comparisons between the PSD determined by 2D-SEM, mercury intrusion capillary porosimetry (MICP), and low-temperature nitrogen adsorption/desorption (LNA/D) were made. The results show that the complexity of shale pore structure can be quantitatively characterized by the pore distribution extracted from 2D-SEM images. In general, the higher the fractal dimension of pore morphology is, the more complex the pores become; and a higher fractal dimension of pore radius usually results in a more complex PSD and a higher proportion of micropores. The PSD of shale can be precisely characterized by the continuous pore size distribution (C-PSD) method. The PSD determined from the 2D-SEM has a good consistency with that determined from the MICP and LNA/D, if the radial step increase is set to half of the average radius of pore throat. The PSD determined from the 2D-SEM is affected by the resolution and the heterogeneity of the pore distribution, so that the PSD should be determined from the high-resolution region representing the pore structure of shales (or the patchwork spliced by multiple high-resolution SEM images). The pore structure of shales can be precisely characterized by 2D-SEM images, providing a new method for investigating the pore structure of coring, and for shales that are difficult to prepare samples. |
| Key words: scanning electron microscopy fractal dimension pore size distribution pore structure shale |
