Experimental study on drilling efficiency with compound axial and torsional impact load

Compound axial and torsional impact (CATI) has been widely considered as a highly efficient assistant drilling technology. However, the rock-breaking mechanism of CATI is still unclear due to the lack of experiments on this new drilling method. Therefore, an impact-drilling experimental device was developed to investigate the influence of the impact angle (load direction), amplitude, and frequency on the drilling efficiency. The results show that impact angles that are too large or too small both have negative effects on the bit performance. There is an optimal impact angle for certain combinations of impact amplitude and frequency, and the range of the optimal impact angle is 40°–60° under the test conditions of this study. The optimal impact angle decreases with the increase of the impact amplitude. Increasing the impact amplitude or decreasing the impact frequency can increase the drilling efficiency of the Polycrystalline Diamond Compact (PDC) bit. This study reveals the rock-breaking mechanism of the compound axial and torsional impact drilling technique and provides a reference for designing such drilling tools.