Experimental study on pore structures of hard coal with different metamorphic grade based on fractal theory

The development features of the pores in the coal reservoir would control the adsorption-desorption and diffusion performances of the gas in the coal. In order to study the pore structure feature differences of the hard coal with different metamorphic grade, a means combined with mercury intrusion method and liquid nitrogen adsorption method was applied to measure the full pore diameter and pore structure distribution of three hard coal samples from No.3 seam of Yuanzigou Coal Mine, No. 2 seam of Yaojie No. 3 Mine and No. 8 seam of Wolonghu Mine. A fractal theory was applied to compare and analyze the pore structure of the hard coal with different metamorphic grade. The study results showed that the three different metamorphic grade hard coal from Yuanzigou, Yaojie and Wolonghu would all have rich opened pore features. With the metamorphic grade increased, the coal porosity would have a high-low-high variation law. The pore of the coal samples from Yuanzigou, Yaojie and Wolonghu would be ink bottles and taper holes mainly. The pore of Yaojie coal samples was mainly in a cylindrical pore. In comparison with the fraction dimension of the pore structure, the pore fraction dimension of Yuanzigou coal sample would be the max and the pore fraction dimension of Wolonghu coal sample would be second. The pore structure of Yaojie coal sample would be relatively simple and also would have a high-low-high variation law.