Multiscale Experiments and Multifractal Analysis of Bituminous Coals: Dominant Pore Properties for Gas Permeability

Abstract

Abstract The pore characteristics of coal are highly correlated with gas permeability. In this study, multifractal analysis based on mercury intrusion porosimetry (MIP) was used to investigate the pore spatial distributions and heterogeneity of pore size distributions (PSDs) of three sister coal samples collected from the Xin Zhouyao mine in China. The mercury intrusion data, under pressures of over 10 MPa, were corrected in combination with the gas adsorption results. All CT images were processed by using the Image-Pro Plus® (IPP) software (Media Cybernetics, Inc., Rockville, MD). The pore volume percentage information obtained from the MIP was found to be coincident with the 3D reconstructions. Seepage experiments were also carried out under different gas pressures to analyze the effect of the pore parameters on permeability. The results from these experiments showed that for the three coal samples, the degree of clustering of the pores is the dominant factor for permeability and should be the first factor considered. Variations of μ (q, ϵ) versus ϵ indicated that the PSDs of coals have multifractal behavior. Multifractal analysis was suggested by the extracted parameters from the PSDs, including the capacity dimension D0, the information dimension D1, the correlation dimension D2, the widths of the right side D0–D10, and of the left side D−10–D0 of Dq spectra, and the widths of left side α0–αq+ and right side α0–αq− of the f (α) spectrum. These parameters were further discussed to evaluate the permeability.