Quantitative Characterization of Fracture in the Coal of Shanxi and Taiyuan Formations Based on an Image Processing Method and Multifractal Theory

摘要

The fracture system is the main transport channel of coalbed methane (CBM), and its quantitative characterization is crucial for the production of CBM. This paper takes the Lower Permian Shanxi Formation and Taiyuan Formation coals as examples; by the microscopic observation and mathematical analysis method, the development characteristics of the fracture system in the coal are systematically studied. The image processing technique is used to obtain the height resolution images (with an actual resolution of approximately 2 mu m) of the fracture in the coal, then multifractal theory is used to study the microfracture structure, and an algorithm is proposed that can quantitatively characterize the multifractal characteristics of coal fractures and its corresponding steps. The quantitative characterization of the whole and part of the fracture structure's heterogeneity combined with the description of the characteristic parameters calculated by the generalized dimension spectrum and the singularity spectrum. Our results show that the heterogeneity of fracture system distribution in samples collected from the Hunyuan area is stronger than that from the Puxian area. For the samples of various coal seams collected from Puxian, the heterogeneity of the distribution of the fracture system of 10# coal seam is the strongest, followed by that of 2# coal seam and 3# coal seam has the highest homogeneity.