The Theoretical Prediction Model of Reasonable Pre-draining Time of Gas in Coal Seam

In order to plan pre-draining time of gas from extracting seam reasonably, coal seam is counted as double media with pores and cracks. Considering seepage, diffusion and desorption process of gas, the gas flow equation is built up. The solver with MATLAB is work out, and the prediction method of reasonable pre-draining time is discussed. The solver is applied in workface of 4(#) coal seam of north area of Sha qu mine, and gas pre-draining rate curve is obtained with time in different holes space. The results show that in same pre-draining time, the smaller holes space is, the greater gas pre-draining rate is. Under the condition of 5m holes space, and in the demand of 30% pre-draining rate, the reasonable pre-draining time is 200d, which is close to the actual result. The theoretical method does not need drilling in the field, which could reduce on-site work and avoid the problem such as drilling and sealing quality, uneven distribution of gas and others, as provide dependable basis for gas pre-draining management. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of China Academy of Safety Science and Technology, China University of Mining and Technology(Beijing), McGill University and University of Wollongong.