Construction technology and development tendency of high level borehole for gas drainage in goaf

In order to solve the high construction cost,low efficiency and other problems existed in the gas drainage from the goaf of the coal mining face with the s pecial gateway and pipeline buried method,based on the gas drainage technical principle of the goaf and top corner with the high level borehole in the roof,a coal and g as simultaneous mining system established with the pre-drainage borehole and high level borehole was provided.The advantages and disadvantages of the high level b orehole constructed with the available rotary drilling technology and the sliding direction drilling technology were analyzed.The paper introduced the new developed met hod and experiment application of the complex direction and large diameter rotary reaming drilling technology.The completed depth of the high level direction drilling co uld reach to 1 026 m and the reaming diameter could reach to 153 mm.Meanwhile ,according to the small diameter of the once completed borehole,slow speed of secon dary rotary reaming,gas drainage channel jammed by the open completed borehole and other problems existed in the present high level direction drilling borehole,the d evelopment tendency of the large diameter once completed borehole technology,complex reaming drilling technology and screen pipe completed technology were provi ded,so as to further improve the once completed diameter dilling efficiency,dilling depth and borehole utilization time of the high level directional drilling,to reduce the construction risk and to improve the borehole economics as well as the gas drainage effect.