# Study on Mechanism of Stick-Slip Vibration Based on Torque Characteristics of PDC Bit
## 1 Introduction  
Polycrystalline diamond compact (PDC) drill bits are a type of drilling equipment used in the oil and gas industry. These drill bits are equipped with synthetic diamond cutters that have been carefully engineered to provide superior strength and wear resistance. When a PDC bit is drilling in gravel-bearing stratum, soft-hard alternating stratum, directional drilling, and other complex working conditions lead to impact loads. These impact loads mainly originate from longitudinal, transverse, and torsional vibration of the drill string system. In particular, the impact load introduced by longitudinal vibration can impose an impact force of up to several tons on the cutting teeth. SV is the most dangerous, facilitating the transition of the cutting teeth into a reverse cutting motion. The impact load often encountered leads to abnormal fatigue failure accidents such as cutting teeth breaking, delamination, and tooth breaking, all of which dramatically reduce the service life and drilling efficiency of the bit [1; 2; 3; 4]. Moreover, SV of the drill string system is the main cause of PDC bit fatigue failure [5; 6; 7]. The causes of SV include cementation of cuttings and blockage of a heterogeneous formation, change in lithology, transverse vibration in compound drilling, etc. [8; 9; 10; 11]. When a PDC bit produces SV, this will aggravate abnormal fatigue damage of the bit, which will reduce rock-breaking energy during its service life, resulting in a decrease in drilling efficiency and possible wellbore safety risks [12; 13; 14; 15; 16; 17]. Therefore, research on the torque characteristics of PDC bits to reveal the mechanism of SV is very important for the technical means and application technology to suppress SV and improve drilling efficiency and safety. [PERSON] et al., [PERSON] et al., and [PERSON] et al. [18; 19; 20] studied the causes and formation mechanism of SV and put forward a technical means to eliminate drill string vibrationthrough the bottom hole assembly. [PERSON], and [PERSON] et al. [21; 22] proposed a PDC bit penetration depth adjustment control technology as a control for bit SV suppression. Implementation of this technology significantly improved the antivibration performance of the bit. [PERSON] and [PERSON], [PERSON] et al., and [PERSON] et al. [23; 24; 25] used bit vibration sensors to identify the SV characteristics of PDC bits caused by cutting and proposed a control to reduce SV by optimizing drilling parameters. [PERSON] et al. [26] studied the influence of cutting depth per tooth and rock drillability on SV of PDC bits through indoor dynamic rock-breaking experiments. [PERSON] et al., [PERSON] et al., [PERSON], and [PERSON] et al. [27; 28; 29; 30] examines the effectiveness of active control of the braking coefficient, using an On-Off-based control scheme with proportional control. The results show that active control can improve the drill string behavior both when drilling and when rotating off-bottom by reducing the slippage of the sleeves. [PERSON] et al., [PERSON] et al., [PERSON] et al., [PERSON] et al., and [PERSON] et al. [31; 32; 33; 34; 35] established a longitudinal-transverse-torsional coupling vibration model and SV characteristics of drill strings in ultra-high-temperature and high-pressure curved wells. The influence of rotary table speed, weight on bit (WOB), torsion punch speed-up tools, and bottom hole assembly length on SV characteristics of drill string systems was explored. [PERSON] et al., [PERSON] et al., [PERSON] et al., [PERSON] et al., and [PERSON] et al. [36; 37; 38; 39; 40] conducted research on rock-breaking mechanisms and drilling rock breaking of separated impact-scraping composite bits that has important reference value for the development and application of new impact-scraping composite PDC bits. The penetration depth of PDC bits with different structures during drilling is crucial to the load on the drill string system.