Experimental Investigation of CS2 Extraction to Enhance the Permeability of Coal

To examine the permeability enhancement effect of the carbon disulfide (CS2) extraction on block coal samples, in this study, different cylindrical samples of anthracite coal were selected to conduct CS2 extraction experiments. Comprehensive measurement techniques, including Fourier transform infrared spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption, industrial computed tomography, and permeability measurements, were employed to analyze the variations of in the chemical structure, microcrystalline structure, pore–fracture structure, and coal permeability before and after the CS2 extraction treatment. The results showed that CS2 extraction can improve the connectivity of multi-scale migration channels, with which the coal permeability can be enhanced. Also, it was found that the permeability enhancement performance by the CS2 extraction is related to the coal anisotropy, as the coal permeability in the vertical bedding direction is smaller than that in the parallel bedding direction before and after CS2 extraction. Also, the CS2 extraction had a time effect on enhancing the coal permeability, and the permeability enhancement was more significant after a longer period of CS2 treatment. It can be predicted that the permeability can be enhanced up to more than 1 mD when the extraction time exceeds 6 h. Also, we concluded that CS2 fracturing is worth exploring by the on-going studies to enhance the permeability and CBM recovery in low-permeability reservoirs.