Permeability Enhancement Properties of High-Pressure Abrasive Water Jet Flushing and Its Application in a Soft Coal Seam

2021 
High-pressure abrasive water jet flushing (HPAWJF) is an effective method used to improve coal seam permeability. In this paper, based on the theories of gas flow and coal deformation, a coupled gas-rock model is established to investigate realistic failure processes by introducing the equations for the evolution of mesoscopic element damage along with coal mass deformation. A numerical simulation of the failure and pressure relief processes is carried out under different coal seam permeability and flushing length conditions. The distributions of the seepage fields and the gas pressure fields of the realistic failure process are analyzed. The effects of flushing permeability enhancement in a soft coal seam on the gas drainage from boreholes are revealed using a field experiment. The conclusions can be extracted that the gas pressure of the slotted soft coal seam is reduced, and the gas drainage volume is more than three times that of a conventional borehole. The field tests demonstrate that the gas drainage effect of the soft coal seam is significantly improved, the tunneling speed is nearly doubled. The results obtained from this paper can provide guidance to gas drainage in soft coal seams regarding the theory and the practice application of the HPAWJF.
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