Research and Application of Borehole Extrusion Prevention Device for Borehole Drilling of Gas Drainage

According to the borehole extrusion occurred at the drilling operation in the soft and high ground stress outburst seam, which would cause the gas conte nt over limit and coal dust outburst problems, a borehole extrusion prevention device was designed.The protection device was consisted with the borehole sealing devic e, the connection device and the gas and water separator.The high gas in the extrusion could be directly drained with the mine gas drainage pipeline and the water and coal fines could be connected with the collection system.Thus the gas, water (drilling water) and cuttings (coal fine) could be effectively separated.The site trial in Song zao Mine showed that when the device applied, the average time of drilling through seam was increased by 79.1%, the average depth of drilling through seam was incre ased by 114.7%, the gas volume fraction at the drilling site was 0. 15%0.25% and was far below the gas allowed content of 1%.