Abstract
Dry coal samples and coal samples with different water invasion times (DWITs) were prepared, and X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and low-pressure nitrogen adsorption (LPNA) experiments were carried out to analyze the pore fracture volume and distribution. The fractal dimension of the aperture surface was calculated with the MIP and LPNA data of these coal samples. We found that the pore diameter of macropores decreases, and the fractal dimensions of macropores and mesopores change greatly, on the score of the dispersion of clay minerals and clay expansion; in addition, water intrusion has little effect on the pore size and fractal dimension of minipores and micropores with increasing water invasion time. We conclude that long-term water invasion greatly damages the pore diameter and surface morphology of macropores and mesopores and reduces the permeability of the fractures in coal seams. Long-term water invasion causes little damage to the pore diameter and surface morphology of minipores and micropores. Water plays an important role in sealing off gas and competing for gas adsorption position in minipores and micropores. In addition, by combining the fractal dimension data of MIP and LPNA, we found that water invasion for 20 days was an effective time point to change the pore structure and surface morphology of coal particles. We anticipate that the research conclusions could save coal seam water injection time, and the conclusions could improve the efficiency of natural gas extraction and improve coal and gas outburst prevention engineering.
Published Version
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