ParametersOptimization Design Of Gas Drainage Boreholes In Virgincoal Seam In Dafosi Mine

In 2011, Dafosi mine became one of gas control demonstration mine. From then on, however, gas volume of every 100m holes has declined significantly, the possible reasonis that the relation of spacing, length and drainage time are not fully considered, especially the hole length, which result in the increase of the engineering quantity.In order to study the relationship between borehole spacing, length and drainage time, according to the main form of existing drainage borehole in Dafosi mine, this paper based on the theory of fluid flow in porous media,combined with gas adsorption and desorption equation,the pressure distribution equation and flow equation of the three kinds of borehole combination are derived, and the method of integrating hole spacing, length and drainage time is proposed in this paper. Simulated the variation of gas flow with time based on the parameters of coal seam and borehole in grouting lane of 40117 face, compared the characteristics of gas flow in different borehole combinations, the conclusions is:in the initial stage, the drainage rate was largeand the flow rate was down fast for parallel borehole.Based on the relationship between the flow and the concentration, the concentration of the bedding drilling in the grouting lane at 40117 working face were analyzed, and the measured concentration of the majority of the borehole was in agreement with the calculated concentration.Finally, the relationship between borehole spacing, length and drainage time when design different borehole combination is concluded. The length and drainage time are considered mainly for the fan borehole in common drilling method,while the spacing and drainage time are considered mainly for parallel borehole in common drilling method, the three aspects need to be considered at the same time for directional drilling,different spacing in different length, each section can meet the requirements of drainage time.These conclusions could help bedding choice of borehole drilling method and the optimization of drilling engineering quantity.