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Abstract

This paper presents experimental investigations on the porous structure and compressibility of six representative tectonized coals, which were geologically formed because of post-formation tectonic deformation of the coal seam, resulting in various brittle and plastic structure development in the seam, such as fissure and fold. The investigations were carried out using microscopy and mercury intrusion porosimetry, providing experimental information about better characterization of the coal structure for coalbed methane recovery from tectonized coal seams. In combination with measurements of vitrinite reflectance and pore size distribution, the mercury intrusion porosimetry data were further analyzed with the fractal theory and used to determine the pore compressibility of the coal samples. The results show that tectonic deformation mainly reformed the bigger pores (pore size above 100 nm). In general, the increased tectonic deformation led to more open pores and, hence, the enhanced connectivity of the pore network. In fractal analysis, a linear relation was used to fit the mercury intrusion data at high pressure instead of the power law that was typically used in previous studies on ordinary coals. The volume−pressure curves obtained by mercury intrusion measurements for all coal samples exhibit a strong dependence relation with the deformation extent. The pore compressibility of these coals obviously decreases as the deformation extent increased, with only one exception for all coal samples studied. This implies that the weak deformation may be corresponding to a high compressibility. Moreover, the results also show that the rank may be responsible for a significant part of the differences in porosity and pore compressibility as well.

Experimental Study on the Porous Structure and Compressibility of Tectonized Coals

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