Fractal Analysis in Pore Size Distributions of Different Bituminous Coals

Coal bumps, coal and gas bursts are currently the main threats to coal mine safety in China. The physical properties of coal are important determining factors for the occurrence of coal bumps or coal and gas bursts. A series of experiments using mercury intrusion porosimetry (MIP), nitrogen adsorption (NA) and carbon dioxide adsorption (CA) were employed to investigate the pore size distributions (PSDs) of bump-prone coal and gas-outburst coal. Considering the influence of coal matrix compressibility on the MIP experimental data, the MIP data should be considered in combination with NA and CA testing data. The dominant pores of gas-outburst coal are different from those of bump-prone coal. The PSDs of coal samples have multifractal characteristics. However, the multifractal characteristics of two types of coal are different. (Answer to question 1, reviewer 2). A comparison of the multifractal parameters indicated that Xin Zhou Yao (XZY) coal samples have a higher spatial heterogeneity and complexity of their pore size distribution, while Zhao Ge Zhuang (ZGZ) coal samples have a lower heterogeneity and pore connectivity, which may hinder smooth gas flow and lead to a localized collection of gas in coal seams.