Study on multi-fractal characteristics of micropores in coal with different metamorphic degrees

In order to study the multi-fractal characteristics of micropore pore size of coal with different metamorphic degrees, according to the low temperature liquid nitrogen adsorption test data, the multifractal characteristics of micropores of 4 different metamorphic coal samples and the correlation between pore characteristics and metamorphic degrees were studied by multifractal theory. The results show that the micropores of 4 coal samples have the typical characteristics of multifractality. The higher the metamorphic degree is, the stronger the heterogeneity of the micropore distribution of the coal sample is. The micropores have a larger specific surface area, which will provide more adsorption sites for gas and have a larger desorption amount. The micropore pore size of 4 coal samples mostly distributed in the narrow area of the pore space is about 7-9 nm; the micropore structure has obvious heterogeneity under weak deformation. In this region, the larger pore size distribution is uniform. However, on the whole, the relationship between connectivity and metamorphic degree is not obvious, and the pores are dominated by aggregation and uneven distribution.