Quantitative Characterization of Pore Structure Parameters in Coal Based on Image Processing and SEM Technology

Abstract

The pore structure parameters of coal have an important influence on the exploration and development of coalbed methane. In this study, a series of pore structure parameters, including porosity, pore radius, pore throat radius, pore coordination number, pore throat ratio, and specific surface area, are identified, extracted, and calculated in the scanning electron microscopy (SEM) images of coal reservoir samples using algorithms and application programs in MATLAB. Constant rate-controlled mercury injection and low-temperature N2 adsorption experiments were carried out to determine the accuracy of the SEM image-based processing analysis results. Characterization results show that the distribution of pore radius in the target coal samples of different organic matters range from 15 nm to 500 μm with porosity of 1.87–8.31% and radius distribution of 12.7 nm to ~100 μm. A noise-reduction system was constructed to eliminate the optical noise of non-porous features and repair the space affected by binarization noise. It is suggested that the characterization processing in this study is suitable for coal or other organic-rich porous materials with porosity > 2% and pore radius > 15 nm.