Numerical simulation of sectional hydraulic reaming for methane extraction from coal seams

Sectional hydraulic reaming technology has been widely used in China; however, because of the lack of research on mechanisms that reduce coal seam stress, improve air permeability, and promote methane extraction, on-site construction parameters are mostly determined from experience, and the effect is often not ideal. In this study, a stress-damage-flow coupling model for methane extraction was established, and a numerical simulation method was used to analyze the effects of the size and spacing of hydraulic flushing cavities on the pressure relief and permeability of a coal seam. The results showed that the cavities produced by sectional hydraulic reaming have an interactive effect that effectively reduces the stress and increases the permeability of the coal seam. The greater the radius of the cavity, the wider the development range of the stress reduction area and the higher the degree of pressure relief. The greater the increase in permeability, the better the coal seam methane extraction effect under the same extraction conditions. For the same cavity radius, the longest distance of the stress reduction zone was unchanged. The lower the distance between two hydraulic flushing cavities, the more evident the superimposing effect they produced and the wider the pressure relief range of the coal seam. In contrast, when their distance was considerable, there was no superposition effect; this significantly reduced the efficiency of the hydraulic flushing cavities in increasing the permeability of the coal seam. In Gaohe Mine, if the distance between two hydraulic flushing cavities is > 7 m, the superposition effect will disappear. This research provides a theoretical basis for better field application of sectional hydraulic reaming technology.

Automated summary

The study found that sectional hydraulic reaming can effectively reduce coal seam stress and increase coal seam permeability, with a larger cavity radius resulting in more significant effects. Additionally, a smaller distance between two cavities leads to a more evident superimposing effect and wider pressure relief range.