Research and Application of Auger-air Drilling and Sieve Tube Borehole Protection in Soft Outburst-prone Coal Seams

Hole accidents during drilling and borehole collapse during extracting are bottlenecks restricting gas drainage efficiency in soft outburst-prone coal seams in China. The auger-air combined drilling technique and sieve tube mounting method are an alternative solution to these technology bottlenecks. The auger-air drilling technique combines the advantages of “dry style” auger drilling and air drilling. Specially designed blade in drill rod can stir up large particles of coal so that large particles can be brought to ground smoothly using compressed air and is efficient to prevent borehole accidents. After drilling is completed, the sieve tube is tripped in through the inner hole of drilling pipes, and then lifting up drilling pipes, the tube sieve will provide a complete tunnel for gas extraction. Field application proves that with proper drilling parameter selection and appropriate tube install control, it is more promising to double drilling depth and raise gas drainage efficiency.