Compressibility and fractal dimension analysis in the bituminous coal specimens

Abstract

Coal is the typical multi-pore media. Numerous experiments have been done to investigate the pore structure of coal. Mercury intrusion porosimetry is still a popular way to analyze the pore characteristics. Compressibility effect on the mercury intrusion porosimetry data cannot be ignored. So N2 adsorption (NA) and mercury intrusion porosimetry (MIP) were applied to analyze the pore structure of coal. In this paper, the mercury intrusion process was divided into three stages including interpore filling, large intrapore filling, and small intrapore filling. The fractal analysis is an important mathematical method, which is widely used to evaluate heterogeneity in the size-dependent distribution of porosity. The fractal characteristics of pore structures in four coal samples with the same rank were also investigated. Three pore fractal dimensions corresponding to the three stages of mercury intrusion, D1C, D2C, and D3C were calculated with the Brooks–Corey capillary pressure model. Df calculated with Farin model is used to estimate an overall fractal dimension. The correlation between the pore fractal dimension and the pore size distribution (PSD) characteristics was further discussed.