The key technology for drilling pressure-releasing gas drainage hole in roof strata

High-level hole in roof is one of the major approaches to control the gas in gob. During drilling, problems such as difficulty of branching in stratum, out-of-control of the target horizon and rectifying deviation at unstable formation may be encountered. It is different from in-seam directional drilling. The paper elaborated the key technology for drilling of directional pressure-releasing gas drainage hole in roof formation. It has important significance for drilling long hole in roof.