Research and application of drilling technology combined rotary withdirection in soft-fragmentized coal seam

According to the shallow hole depth,track without measured and controlled,directional drilling difficult and other disadvantages existed in the available gas extraction borehole drilling technology applied in soft-fragmentized coal seam,directional drilling with mud pulse MWD was put forward.The technical principle was introduced and a complete set of technology and equipment was formed,with the key drilling technologies had been developed,such as mud pulse wireless transmission technology,drilling technology combined rotary with direction,hydraulic positive cycle and heterogeneous drill rod compound slag discharge technology,directional drilling rig,mud pulse MWD system,mud pump,helical screw motor,special drill rod,filter drill rod,spiral non-magnetic drill rod and directional drill were developed and selected.The field test was carried out in Sihe Mine and Chengzhuang Mine,the results show that four directional drilling were successfully completed with the maximum hole depth reached 402 m,total length was 4 808 m,hole forming rate was 75%,predetermined area of work surface and roadway was successfully covered,which will provides a new technical means for progressive gas extraction in soft-fragmentized coal seam and had important significance for safety and high efficiency mining in coal mine.