Session: 11-01-01 Well Drilling Technology

Paper Number: 123992

123992 - Active Control of Distributed Subs With Anti-Slip Logic for Torsional Vibration Damping in Drilling 

Torsional vibrations can lead to drill string damage and failure. Previous publications showed that damping subs consisting of sleeves distributed along the drill string can reduce low-frequency torsional vibrations, such as stick-slip.

These sleeves are supported on bearings to allow the pipe inside them to rotate freely under normal circumstances and they include a permanent magnet to add viscous damping to the drill string when undesirable vibrations occur. The damping force acting on the drill string depends on the relative velocity between the pipe and sleeve and on a damping coefficient which is adjusted by active control. The highest damping force can be applied when the sleeves are non-rotating. If the damping force surpasses the friction force between the borehole wall and the sleeve, the sleeve slips and starts moving. This can harm both the borehole wall or casing and the tool, especially if the slipping happens more often at the same depth.  

In this paper, an on-off-based controller, which is prone to frequent sleeve slippage, is combined with anti-slip logic. Whenever the sleeve slips, the current damping coefficient and the measured pipe velocity, relative to the sleeve, are used to learn the maximum damping force available in the present situation. The controller uses this information to avoid or minimize slippage. Since downhole conditions can change throughout the drilling operation, slippage of the sleeves must occasionally be allowed in order to learn the new constraints on the amount of damping that can be applied. This logic is reminiscent of the well-known trade-off between exploration and exploitation in reinforcement learning.

Simulations with a transient coupled axial and torsional drill string model are used to demonstrate the effectiveness of the anti-slip logic both for on- and off-bottom conditions representative of a field case from a North Sea well with frequent stick-slip. Results show that the slippage of the sleeves can be reduced, and the vibration-damping capabilities of the controller are improved compared to the baseline on-off controller without anti-slip logic.

Presenting Author: Pauline Marie Nüsse Norwegian University of Science and Technology

Presenting Author Biography: Pauline Nüsse is a PhD student at the Department of Engineering Cybernetics at the Norwegian University of Science and Technology (NTNU). As part of the SFI DigiWells project, she focuses on control for vibration damping in drilling. She holds a Master's Degree in Computer Science in Engineering from the University of Augsburg in Germany.

Authors:

Pauline Marie Nüsse Norwegian University of Science and Technology
Adrian Ambrus NORCE Norwegian Research Centre
Ole Morten Aamo Norwegian University of Science and Technology