| Mining protective layers is one of the most economical and efficient regional measures in preventing coal and gas outburst. In the thesis, in allusion to the characters of complicated geologic structure, shallow buried depth and multi-seam mining of Wulan Mine, protective layer mining and gas extraction by surface well drilling are adopted, the threaten of gas to mine safety production is lowered effectively, and the life safety of mine workers are ensured powerfully.To master the evolution laws of the fracture field in protected coal seams, the experimental study of mining field analog simulation is done, and the computer numerical simulation and analysis is done by UDEC software. After the mining of7#coal seam and8#coal seam,2#coal seam and3#coal seam will be located at a whole subsidence zone. The protective effect of7#coal seam to3#coal seam is obvious, but the protective effect of7#coal seam to2#coal seam is not obvious; after the mining of8#coal seam, the pressure relief effect of3#coal seam will be strengthened, and the pressure relief effect of2#coal seam is strengthened obviously. As the goaf formed after the mining of7#coal seam has buffering effect, the pressure relief effect of overlying remote protected coal seams caused by the mining of8#coal seam is relative weak.The mathematical model of pressure relief gas extraction by single well drilling is set up. The actual measured gas extraction parameters are treated as known quantity, a conclusion of the pressure relief gas extraction quantity of protected coal seams account for58%-93%of pure gas extraction quantity by surface well drillings. The definition of effective extraction range for surface well drilling is put forward, and the maximum well spacing distances of surface well drillings are analyzed on the basis of effective extraction ranges for surface well drillings. The maximum well spacing distances in ventilating roadways and mechanical roadways are all200m. |
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