穿层瓦斯抽采钻孔用随钻式掏穴钻头设计

Design of cavity drill bit while drilling for gas drainage of crossing borehole

为提高穿层钻孔瓦斯抽采效果,目前常采用掏穴钻进技术增大煤层段局部钻孔直径,避免了岩层孔段的无效进尺,但受掏穴钻头结构限制,一般需要在先导钻孔完成后提钻,然后重新下入掏穴钻头进行掏穴钻进,存在工序多、辅助作业时间长的问题。为解决以上问题,采用齿轮齿条结构形式设计了一种随钻式机械掏穴钻头。该钻头在岩层孔段钻进时翼片收回,进入煤层后,利用水力参数的改变推动带齿条的活塞轴向运动,活塞带动带齿轮的翼片旋转并张开,从而进行掏穴钻进;掏穴钻进完成后,翼片缩回,钻头顺利退出钻孔,进行封孔连抽。现场试验结果表明,该钻头能够在岩层段保持闭合时进行先导孔施工,进入煤层后增大泵量时可顺利张开并进行掏穴钻进,增大了煤层孔段钻孔直径,降低了穿层钻孔辅助作业时间,提高了穿层钻孔掏穴施工效率。

In order to improve gas drainage effect of crossing borehole, cavity drilling technology is often used to increase part borehole diameter of coal seam section, which avoids invalid footage of hole section in rock layer. However, due to limitation of structure of cavity drill bit, it is generally necessary to to lift the drill after the pilot drilling is completed, then the cavity drilling bit is put into the hole to carry out cavity drilling, which need more procedures, long auxiliary operation time. In order to solve the above problems, a mechanical cavity drill bit while drilling was designed with rack and pinion structure. The wing is retracted when the cavity drill bit is drilling in the rock layer. After entering coal seam, axial movement of the piston with rack is driven by change of hydraulic parameters, which drives the pinion blade to rotate and open to ream drilling. After caving drilling is finished, the wing is retracted, the drill bit is pull out from the drilling hole, and the hole is sealed and the gas is pumped. The field test results show that the drill bit can construct pilot hole when rock is closed, and can open smoothly and carry out hole cutting drilling after entering coal seam and the pump volume is increased, which increases the diameter of borehole in coal seam, reduces auxiliary operation time of crossing borehole,improves construction efficiency of crossing borehole.