Study on adaptability of PDC bits under dynamic loading based on micro-drilling test rig

Abstract:

Rotary-percussive drilling with PDC bits is an effective method for improving the rate of penetration （ROP） in hard formations. However， most existing experimental devices for PDC bit impact rotary drilling lack convenient control over parameters such as impact load amplitude and frequency. To investigate the variation laws of ROP for both unworn and worn PDC bits under different static and dynamic load parameters， PDC bits with varying degrees of wear were designed and manufactured. Drilling experiments with controllable dynamic load parameters were conducted using a modified servo feed micro-drilling test rig， focusing on analyzing the effects of static load， dynamic load mode， as well as dynamic load amplitude， proportion， and frequency on bit ROP. The results indicate that： under static load drilling， the wear of bit cutters significantly reduces drilling efficiency； compared with static load drilling， the average ROP of unworn and worn PDC bits increases by 21.5% and 35.2%， respectively， under dynamic load drilling. The dynamic load proportion and frequency have a significant influence on ROP. With the maximum total axial load kept constant， the ROP of both unworn and worn PDC bits shows a decreasing trend as the dynamic load amplitude increases. Within the experimental parameter range， both types of bits achieved optimal ROP at a dynamic load frequency of 10 Hz. The research results elucidate the operational behavior of PDC bits under dynamic loading conditions， thereby offering an experimental foundation for optimizing drilling parameters and selecting appropriate bits for percussive-rotary drilling in deep hard formations.