Rock fragmentation mechanism and application of near-bit torsion impacter

PDC bit is the main rock-breaking tool in hard formation of ultra-deep wells. Its premature failure due to the stick-slip vibration is an important factor that results in increasing the drilling cost in ultra-deep wells. According to its stick-slip vibration effects, this paper analyzed stick-slip vibration mechanism theoretically, established the mechanical model of PDC bit stick-slip vibration system, and used high frequency-low amplitude torsion impact generator and bit structure optimization, for eliminating the drill stick-slip vibration. The results show that: length of PDC bit is longer, as a result, energy decays faster and energy transfer efficiency of torsion impacter is lower; section area is larger, as a result, length is smaller and energy transfer efficiency of high-frequency torsion impacter system is higher; Xinjiang Tarim Basin XK3 Well tests show that torsional impact tools could improve penetration rate more than doubled compared with the conventional drilling, could eliminate the stick-slip vibration effects of PDC bit, and could reduce the drilling string torsion oscillations and the drilling cost.