Optimization Analysis And Application Of Slotted Borehole Layout In Coal Roadway Strip

Borehole layout is the key of the methane drainage effect, which should bedetermined by coal seam condition and drainage time. When high-pressure water jetslotting is used in the cross borehole of roadway strip, the slot size as well as thedrainage time after slotted are all not clear, which led to blindness strongly in slottedborehole layout. Therefore, researching the optimization of slotted borehole layout incoal roadway strip has a significant meaning in coordinating the temporal relationbetween coal mining and methane mining and adapting mine production deployment.By integrating theory with numerical simulation in this paper, the stripe’s drainagetime in different coal seam condition as well as different borehole layout was studied,and the borehole layout of the W2704S strip was optimized. Then the results wereverified by the field tests. The main conclusions are stated as follows:①The coal slotting size was calculated theoretically by combined with the similarmodel experiment results of high-pressure water jet slotting and based on themomentum theorem and continuum damage mechanics theory, which prepared the slotsize in different coal seam condition.②Dynamical evolution model of permeability and porosity as well as D-P criterionwere introduced to build the fluid-solid coupling model of methane seepage in the lowerpermeability slotted coal seams, and the coupling model was calculated based on thesecondary development of the COMSOL soft. Results show that borehole radiusincrease with the conduction of drainage, and there is a significant exponential relationbetween them; coal seam methane migration was affected by the slotted borehole layoutarrangement, while the cross arrangement was more reasonable; relation expression ofdrainage time with slot size, borehole spacing, permeability, coal buried depth andmethane pressure gradient was built to guide the reasonable borehole layout.③Coal slotting size was calculated by the dimensioning formula in W2704S returnairway strip, and the borehole arrangement was optimized based on the numericalresults. Field experiment results show that the relative error between the numericalcalculation time and the actual time is7.9%, which verifies the rationality of the slottedborehole layout optimization way in coal roadway strip.