Comparison of Hydraulic Measures for Improving Coal Seam Permeability: A Case Study

Hydraulic measures are widely used to improve coal seam permeability, but not all hydraulic measures have a positive effect on coal permeability in soft coal seams, and the permeability-enhancing effect of hydraulic measures in soft coal seams is not clear. To further study the permeability-enhancing mechanism of hydraulic measures and compare the effect of hydraulic punching and reaming in soft coal seams, this study takes Changping Mine, China, as its case study. A comparative analysis was conducted on the influence range and gas extraction effect of hydraulic reaming and punching on coal seam permeability enhancement. The following conclusions were mainly drawn: A mathematical calculation model was established for the strength and impact velocity of high-pressure water jet damage to the coal body, and the critical theoretical pressure threshold and jet velocity were obtained. During the implementation of hydraulic measures at the Changping Mine, the effective radius of hydraulic reaming is around 4.5 m, and the influence radius of hydraulic reaming is approximately 7.5 m; the effective radius of hydraulic punching is about 6.5 m, and the influence radius of hydraulic punching is approximately 7–9 m. The gas data from field monitoring show that hydraulic measures have significantly improved the extraction gas concentration and purity, and hydraulic punching has a more significant effect on enhancing permeability in soft coal seams.