Drillstring Vibration Damping

Challenge

Drilling of complex well trajectories is often hindered by downhole drill string vibrations and stick-slip These can lead to drill bit and downhole tool damage, tool-joint and drill string wear possibly leading to a twist-off, or formation damage. Recent advancements in drill string vibration interpretation show that the sources of excitation are not only at the bit but anywhere along the string. Today’s top-drive solutions with soft-torque/soft-speed and Z-Torque help mitigate stick-slip. However, server drill-string vibrations can still occur especially for long wells with long horizontal sections. 

Innovation

A novel method for mitigating stick-slip vibrations uses magnetic damping elements distributed along the drill string. Each damping sub has a slightly larger diameter than adjacent tool joints, lifting the string off the borehole wall to reduce mechanical friction. Rotary eddy current brakes introduce viscous friction, effectively damping torsional oscillations. To minimize axial drag, the subs move on spur wheels supported by bearings, decoupling axial and rotational motion—key to reducing vibrational excitation. Simulations using a 4-degree-of-freedom torque and drag model confirm performance gains.

A test bench was built to evaluate damping effectiveness. By adjusting the magnetic field, braking force varied linearly with rotational speed. Experiments demonstrated the system’s ability to suppress torsional vibrations and mitigate stick-slip.

The subs also allow active control of damping strength. Simulations show that distributed control algorithms can achieve effective damping with fewer subs. Coordinated sleeve control enables low-amplitude lateral drill-string movement, aiding hole-cleaning while reducing torsional oscillations.

Value

• Vibration can cause damages to drillstring, tool-joints and to expensive downhole equipment. By reducing the vibration such damages can be reduced and even avoided.
• Stable conditions at bit improves drilling efficiency.
• The damping subs reduce the overall required torque at the top-drive and facilitate weight transmission to the bit. Simulations have shown that torque reduction can reach more than 50 percent. A more modest 30 percent decrease is assumed to account for the fact that the tools will not always be lying in part of the well where contacts are significant. This decrease in friction directly affects the electrical energy consumption of the top drive. When drilling long horizontal sections, the savings in cost and CO2 emissions can be significant.
• The concept is patented.
• Enhanced hole cleaning can be achieved by active control of the distributed damping subs to trigger the lateral movement of the drill-string at certain positions which can open the possibility to control wobbling of drill-string. 

Next steps

• Apply for a verification project with the aim to build and test full-scale damping tools without active control.

This work is part of the centres workpackage 5: Drilling automation and autonomy