Comprehensive Fractal Model and Pore Structural Features of Medium- and Low-Rank Coal from the Zhunnan Coalfield of Xinjiang, China

Medium and low-rank coal from the Zhunnan coalfield of Xinjiang in China was investigated for quantitatively characterizing its range of aperture structure. The pore parameters were determined by nitrogen adsorption at low temperature and mercury injection at high pressure, and the full aperture was determined. The FHH model, Menger model, Sierpinski model, and a thermodynamic model were used to calculate the comprehensive fractal dimension of the coal samples over the full range of aperture. The fractal characteristics of the pores of medium- and low-rank coal were quantitatively analyzed, which provided a reference for the overall characterization of pore structure heterogeneity in this coalfield. The results show that the FHH model and thermodynamic model more accurately calculate the fractal dimensions of less and greater than the joint pore position, respectively. The comprehensive fractal dimension of the low-rank coal pore is 2.8005–2.8811 and that of medium rank coal is 2.5710–2.6147. When compared with the medium-rank coal, pores of the low-rank coal are more developed and they exhibit a more complex structure with stronger heterogeneity. The comprehensive fractal dimension of the pores is a negative correlation with average pore size, vitrinite content, and maximum vitrinite reflectance, and positive correlation with pore volume, pore specific surface area, inertinite content, and exinite content