Experimental investigation on coal pore and fracture characteristics based on fractal theory

Abstract

Coal is an extremely complex porous medium. To study the pore and fracture characteristics of coal, samples from northeastern China were collected and crushed into eight kinds of particle sizes to conduct the experiments using a combination of basic physical parameters, mercury intrusion porosimetry (MIP) and N2 (77 K)/CO2 (273 K) adsorption pore structure characterization. At the same time, the scale characteristics of the coal pores and fractures were analyzed by fractal theory. The results indicate that the pores and fractures in coal become increasingly simpler and are more favorable for gas storage and migration during the crushing of the coal samples. The fractal curves of the pores and fractures in coal samples with different particle sizes determined from MIP were all divided into two parts by an inflection point. According to fractal theory, the width that corresponds to the inflection points of the fractal curves are considered to be the critical value for determining the pores and fractures in coal. On this basis, the matrix porosity and the fracture porosity in coal were obtained by combining the data from the MIP and N2 (77 K)/CO2 (273 K) adsorption. It is believed that this study is of great significance to analyze the coal permeability evolution law affected by the dual-porosity coal structure characteristics.