Research on damage distribution and permeability distribution of coal seam with slotted borehole

In order to study the effect of high pressure water jet cutting technology on the permeability of single coal seam, we use the damage variable to describe the fracture distribution of coal seam, develop the 3-D finite element program based on the damage theory, and then analyze the damage distribution of coal seam after drilling and slotting. Using MTS815 rock mechanics testing system and the permeability test system, we conduct the permeability test and get the relationship between permeability and damage. Based on the damage distribution of coal seam after drilling and slotting and the permeability change law, we analyze the permeability distribution of coal seam after drilling and slotting. The results show that: after slotting high damage appears in the coal seam around the slot, which is advantageous for gas flow and expands the effect range of the drill. The slot width has little effect on the permeability of coal seam while the slot height has the obvious effect on permeability of coal seam. It is necessary to expand the slot height for increasing the effect range of the drill.