Multifractal Characterization of Tectonically DeformedCoal Pore Structure Based on Mercury Injection Technology

Depending on coal samples of Hancheng mining area in Weibei coalfield, the heterogeneity of pore size distributions (PSDs) of tectonically deformed coals (TDCs) was analyzed based on the mercury injection technology and the multi fractal theory. The multifractal spectra f(a) was calculated and the change law of multifractal parameters was studied with tectonic deformation degree increasing. The results indicated that the PSDs of coals mercury injection exhibited multifractal characteristics, but the degree of multifractality showed significant differences for different TDCs. With the tectonic deformation increasing, the f(a) spectra changed from right hook occurred in cataclastic coals to left hook occurred in granulated coals and mylonitic coals, while values increased, including the singularity index α₀, the f(a) spectra width (α_q--α_q+), and the left side width (α₀-α_q+) of f(α) spectra, which illustrated that the strong brittle tectonic deformation and the ductile deformation could lead to the complication of pore structure easily, the pore clustering feature enhanced, the heterogeneity of high concentration of pore volume increased and the permeability decreased. α₀ and α₀-α_q+ could be considered as major indexes to distinguish tectonic evolution for PSDs of TDCs. Some factors resulted in the variation of multifractal parameters, such as the shift of the maximum peak of pore volume, the generation of granulated pores and the uneven distribution of microstructure.