Friction Reduction Law of Compound Drilling in Directional Deep Hole of Underground Mine

The compound drilling technology has positive significance to improve drilling efficiency, the borehole depth, and to promote the borehole condition and trajectory controlling accuracy, especially for directional deep hole, compound drilling technology can play a good role in reducing friction. Slip turning ratio concept is proposed by the analysis of drill string motion state. Dynamic finite element analysis is used to study the effect of speed and feeding speed on the friction, and the influence of slip turning ratio and friction reduction efficiency is obtained. The results of simulation analysis are verified by field test, and the compound friction reduction and directional drilling technology for hard rock is summarized.