Study On Increasing Permeability And Extraction In Low Permeability Coal Seam By Static Blasting Technology

In this paper,the static blasting technology,which has been applied in surface rock fracturing,is introduced to increase coal seam permeability and improve gas extraction.The influence of guide hole arrangement,borehole diameter and borehole spacing on stress field evolution and damage zone distribution is studied by theoretical analysis,experimental research and numerical simulation.Besides,the stress-damage-seepage coupling model is used to investigate the application effect of static blasting technology in coal seams,which provide theoretical basis and guidance for improving coal seam permeability and increasing gas drainage effect.The research results show that:(1)The crack initiation of double holes depends on the stress superposition between blasting holes,whereas that of guiding holes depends on the free surface inside the coal body.The increase in borehole diameter and spacing reduction between boreholes could improve the static superposition breaking effect.The guide hole arrangement can play a role in guiding the development direction of fractures and enhancing the effect of fracturing.(2)The relationship between the guiding hole,borehole diameter,and borehole spacing was revealed from the two aspects of the stress field and damage zone.The purpose is to strengthen the fracturing effect.The drilling diameter and spacing are measured,and the guide hole strengthens the fracturing effect.At the measurement level,it should be analyzed from the two dimensions of time and stress.The time dimension accelerates the migration of the stress turning point,whereas the stress dimension realizes stress superposition and finally strengthens the static cracking effect.(3)The development of coal seam fractures is affected by the coal stress state,construction parameters,and elastic modulus.Construction parameters affect the stress state of coal body,fracture development reduces the elastic modulus of coal body,and promotes the further expansion of fracture under the combined action of stress state and elastic modulus.The coal body mainly experienced the following five stages of fracturing: coal body compaction,micro-damage formation,micro-fracture formation,large-fracture formation,and fracture propagation.Besides,the guide hole arrangement can play a role in guiding the development direction of fractures.(4)For low-permeability coal seams(permeability coefficient 0.01 m/d),the effective influence radius of conventional extraction is 0.3m,the effective influence radius of fracture extraction in the horizontal direction is 1.54 m,and the effective influence radius of fracture extraction in the vertical direction is 0.86 m.Compared with conventional extraction,the effective influence radius in the horizontal direction increases by 5.1 times,and the effective influence radius in the vertical direction increases by approximately 3 times.After the application of static blasting technology,the permeability of the coal seam greatly increases,and the gas flow in the coal seam accelerates,resulting in a sharp decline in gas pressure in the fracturing area near the extraction hole.This paper contains 48 figures,6 tables and 90 references.