分析了其中4种孔底换钻头钻具的结构及工作原理；
The esigns and working principles of 4 types of it are analysed.
介绍了垂线孔孔底随钻跟踪定向纠偏新技术和施工效果，最后结合实例谈几点认识。
It also describes the new techniques and the results drilling tracing of deviation correction in the construction of the bottom of the plumb line hole. Finally, several views are out forward.
介绍了垂线孔孔底随钻跟踪定向纠偏新技术和施工效果，最后结合实例谈几点认识。
It also describes the new techniques and the results drilling tracing of deviation correction in the construction of the bottom of the plumb line hole. Finally, several views are out forward.
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