Abstract
Stick–slip vibration is common in the oil well drilling process and is detrimental to down-hole equipment and drilling efficiency. In recent years, a new type of drilling technology, torsional impact drilling, has been developed to mitigate the stick–slip phenomena, particularly in the drilling of deep or abrasive formations. With this drilling technique, high-frequency torsional impacts are generated and applied to the drill bit, providing the drill bit with auxiliary energy. By mitigating or suppressing the stick–slip vibration, part of the energy wasted as a result of vibration can be regained. However, the effect of these impact loads on the dynamic response of a drill string in a stick state is unknown. In order to address this issue, a continuous system model of a drill string that includes torsional impact load was constructed. In the model, a Fourier series approach was used for the impact load, and the mechanical model was resolved with the mode superposition method. Case studies were done to understand the drill string dynamics, with and without the impact. The case study results demonstrate that high-frequency torsional impacts have little influence on the dynamic response of a drill string in a stick state.
Highlights
Friction-induced stick–slip vibration decreases the performance and safety of operation in a wide range of engineering problems, such as machine tool sliding[1] and squealing brakes.[2]
The problem of stick–slip vibration, which is detrimental to drilling equipment and drilling efficiency, was studied
The dynamic response of the drill string was a combination of the mode shape and the principal coordinate
Summary
Friction-induced stick–slip vibration decreases the performance and safety of operation in a wide range of engineering problems, such as machine tool sliding[1] and squealing brakes.[2] In these systems, the combination of friction and movement can lead to system failure. The torque that is applied through the drill string eventually succeeds in breaking the bit free, but the sudden release of the bit causes it to rotate faster than the drill string.[4] Cyclic stress is generated because of the alternation between the stick phase and slip phase, and this leads to fatigue problems in the drill string.[5] In addition, the high bit speed in the slip phase can excite severe axial and transverse vibrations in the bottom hole assembly, which may cause bit bounce, excessive bit wear, and a School of Mechatronic Engineering, Southwest Petroleum University, Chengdu, P.R. China
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