Drill string dynamics and experimental study of constant torque and stick-slip reduction drilling tool

Abstract

Aiming at the problems of large torque fluctuation of drill bit and low weight-on-bit(WOB) transmission efficiency during the drilling process, a novel drilling tool generating constant torque and reducing stick-slip is proposed. For investigating the further dynamics behavior of drill string system, the mathematic models are established based on the new tool output characteristics. Also, compared with field test and application, the drilling tool effects on increasing ROP (rate of penetration) and reducing drill bit wear are verified. The research results show that the peak value of drill bit angular velocity increases gradually with the bigger value of the pre-compression of disk spring system, so as the rotary table inputting speed, during drill bit downward movement. About the drill string influence, the larger the length of drill string, the longer response time is the rotating angular velocity of drill bit. Another one, the shorter the steady time of drill bit angular velocity, the bigger ratio is the stick-slip within one period. This new drilling tool can effectively improve the drill bit force conditions, and reduce the stick-slip stage, which can also profitably increase drilling efficiency and the service life of downhole tools, especially in ultra-deep or long distance horizontal wells.