Research on how acidification affects the coal's microscopic pore structure in the Guizhou mining region

Abstract By eliminating their minerals, acidification technology makes coal seams more permeable. Acidification technology were conducted in the Farr and Qinglong mining areas using a mixed acid solution to study the impact of acidification technology on increasing the permeability of primary structural coals in the Guizhou region, China. The microphysical and chemical structure of the coal samples before and after acidification transformation was compared using X‐ray diffraction, scanning electron microscope, mercury intrusion porosimetry, and Fourier transform infrared spectrometry experiments. The results show that after acidification, the volatile matter content is reduced by 4.2% and 16.25%, the carbon content is increased, the degree of coalification is deepened, the gas content of the coal seam is elevated, and the gas source is more abundant. The minerals on the surface are dissolved to different degrees, and the pores and cracks are dredged, so that the surface of the coal samples shows better connectivity, which is conducive to the diffusion and transport of coalbed methane. The volume and pore diameter of the macropore and mesopore in the Farr coal samples were improved after acidification, and the fractal structure was more prominent, the pore connectivity was good, and the pore diameter of the Qinglong coal samples was greatly increased. The content of oxygen‐containing functional groups increased by 11.2% and 2.1%, respectively, which is conducive to the desorption of coalbed methane after acidification, and with the increasing degree of metamorphism of the coal samples, the higher the content of oxygen‐containing functional groups was and the less pronounced the effect of acidification. Acidification technology can effectively remove the minerals in the coal body and has a good effect on penetration enhancement, and the results of the study can provide certain theoretical references for the penetration enhancement of coal seams in Guizhou mining areas.