Numerical Study On Gas Drainage Borehole Gas Flowrate In Yanma Coal Mine

Borehole gas flowrate is an important index to evaluate gas drainage effectiveness and can only be got from field test at present.In order to analyze the influence factor of gas flowrate,the expression of borehole gas flowrate is deduced on the basis of Darcy law and definition of flowrate at gas steady flow theory..The value of single borehole gas flowrate and hectometre borehole gas flowrate is calculated with 27131 working face coal seam gas parameters?The results showed that single borehole gas flowrate was related to drainage negative pressure,borehole diameter,coal seam permeability and initial gas pressure while coal seam permeability and initial gas pressure had a significance influence to single borehole gas flowrate.Hectometre borehole gas flowrate was related to drainage negative pressure,borehole arrangement and coal seam permeability while drainage negative pressure had little influence to gas flowrate.The decay coefficient of hectometre borehole gas flowrate was increased with the arrangement density of borehole and coal seam permeability added.The field test data from 27131 working face proved that drainage negative pressure was positive related to hectometre borehole gas flowrate and the index of initial speed from borehole gas emission cannot accurately predict coal and gas outburst.