Abstract The characterization of fracture structures is key for evaluating the permeability of coalbed methane (CBM) reservoirs, and an interconnected fracture network is essential for the production of CBM. Taking the Upper Permian coal in the eastern Yunnan and western Guizhou region as an example, we systemically studied the characteristics of coal deformation and fracture development through direct observation of coal faces and hand specimens. An image processing technique was used to obtain high-resolution fracture images (with an actual resolution of approximately 2 μm), followed by the statistics of the porosity parameters such as micro-fracture density, intersection point density, and plane areal porosity. The multifractal theory was applied to study the micro-fracture structures of the coal, and a practical algorithm and corresponding technical procedure was proposed to characterize the multifractal characteristics of coal fractures. The quantitative characterization of the heterogeneity of the whole and partial fracture structure was then performed, and the indicating significance of the generalized dimension spectrum, the singularity spectrum, and the calculated characteristic parameters was described. Our results suggest that the micro-fracture structures of coal are multifractal, which can be measured by combining image processing and multifractal methods. The fracture development and the distribution heterogeneity in the target coal seams show significant differences, both vertically and laterally. Coal seam groups with well-developed fracture systems and high connectivity were identified by combining macro- and micro-scale fracture observations and multifractal characterization, including the 8–12 coal seam group in the Tucheng mining area, the 3–7 group of the Yueliangtian mine in the Pan'guan mining area, the 8–12 group in the Pan'guan mining area, the 13–18 group in the Enhong mining area, and the 3–7 group in the Laochang mining area.

中文翻译：

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基于图像处理和多重分形理论的煤中裂缝结构定量表征

摘要 裂缝构造表征是煤层气储层渗透率评价的关键，而连通的裂缝网络对煤层气的生产至关重要。以滇东、黔西地区上二叠统煤为例，通过直接观察煤面和手标本，系统地研究了煤的变形和裂缝发育特征。采用图像处理技术获取高分辨率裂缝图像（实际分辨率约为2 μm），统计微裂缝密度、交点密度、平面孔隙率等孔隙度参数。应用多重分形理论研究煤的微裂缝结构，提出了一种表征煤裂缝多重分形特征的实用算法和相应的技术流程。然后对整体和部分断裂结构的非均质性进行了定量表征，描述了广义维数谱、奇异性谱和计算出的特征参数的指示意义。我们的研究结果表明，煤的微裂缝结构是多重分形的，可以结合图像处理和多重分形方法进行测量。目标煤层裂缝发育和分布非均质性在纵向和横向上均存在显着差异。