Multi-scale characterization of coal pore and fractures and its influence on permeability—taking 14 large coal bases in China as examples
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Abstract:
In order to explore the characteristics of pores and fractures at different scales and their influence on permeability, nitrogen adsorption, mercury injection and CT experiments were carried out on 14 large coal bases in China. Seepage experiments were then conducted on the coal samples after CT scanning. The results showed that the micropores and transition pores in each coal sample are mostly closed pores with poor connectivity, which is not conducive to coal seepage. The pore and fractures volume with r=10 nm and r=100 μm accounts for a large proportion, contributing most to the porosity of coal. Large-scale parallel plate pores in S2 and S3 provide sufficient space for seepage. By dividing dominant pore size segments characterized by three experiments, a method for comprehensively characterizing porosity and fractal dimension is proposed. The porosity range of each coal sample is from 1.62% to 11.60%, and the fractal dimension range is from 2.29 to 2.78. The permeability of coal samples ranges from 0.000 2×10-15 m2 to 0.652 5×10-15 m2, mainly in medium and low permeability. The relationship between the porosity components of r<50 nm, 50 nm≤r≤8.5 μm and r>8.5 μm and permeability is as follows: y=0.274 1x-0.078 1, y=0.067 4x+0.023 7 and y=0.003 9x2.598 6, respectively. The correlation between the porosity component of r>8.5 μm and permeability is the strongest. Compared with nitrogen adsorption and mercury intrusion experiments, the CT experiment is more suitable for analyzing the influence of pore and fractures on water seepage.
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Supported by National Natural Science Foundation of China (51934004, 51974176), and Shandong Natural Science Fund Outstanding Youth Fund (ZR2020JQ22).
