Geophysical characteristics of anthracites with various structures: a case study on the southern Qinshui Basin, north China

Abstract

Deformation of coals under tectonic movements could cause reduction of mechanical strength and enhancement of gas adsorption, which might result in coal and gas outburst, and cause safety and environmental issues. In this study, geophysical characteristics of coals with various structures were investigated with a special emphasis on characterization of pore size distribution, rock mechanical strength, acoustic emission, resistivity and acoustic velocity of anthracites with three types of structures in the Qinshui Basin, north China. The studied No. 3 coal seam developed three types of structures, namely undeformed coal, cataclastic coal, and granular coal. Petrographic observations under scanning electron microscope and pore size distribution using N₂ and CO₂ adsorption of anthracites of three types show that the undeformed coal consists of primary micropores, and cataclastic coal is mainly composed of mesopores and well-connected fractures. In comparison, granular coal has the least mesopores. Rock mechanical strength, acoustic emission, resistivity and acoustic velocity of coals with three structure types were investigated under uniaxial and triaxial compression. With increasing degree of deformation of anthracites, compression strength, Young’s modulus, density, acoustic emission counting and acoustic velocity decreases, while resistivity increases. We suggest that the evolution of pore size distribution of anthracites with increasing degree of deformation contributed to variations of geophysical characteristics of coals with different structures to some extent.

Graphical abstract

Keywords

geophysical characteristics / coal structures / pore size distribution / acoustic emission / electrical resistivity / acoustic velocity

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Acknowledgments

This research was supported by the National Natural Science Foundation of China (Grant No. 42102194).

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