Poor hole cleaning is often the cause for drilling performance deterioration, many times leading to detrimental situations such as pack-offs and stuck pipe.

In addition to high flowrate and rotational speed, lateral oscillations of the drill-string on the low-side of inclined wells were shown to improve hole cleaning. However, the drill-string lateral oscillations are usually not controlled in any way. This paper proposes a solution to trigger the lateral movement of the drill-string at certain positions, with simulation results to support the novel concept.

Generally, it is desirable to damp out drill-string vibrations as they impact drilling performance, can cause severe damage to drill-string/bottom hole assembly components, or destabilize the formation rocks. A solution based on distributed damping subs along the drill-string has been proposed to eliminate stick-slip and other forms of torsional vibrations. These damping subs utilize magnetic viscous damping through eddy current braking and their design enables active control of the damping strength. The latter fact allows to consider a coordinated control of the damping strength to initiate a controlled low amplitude lateral movement of the drill-string that can facilitate hole-cleaning while simultaneously attenuating torsional oscillations of the drill-string.

A simulated environment was used for verifying the proposed solution. It includes a transient stiff-string torque and drag model which accounts for axial, torsional and lateral displacements. The viscous damping subs are included in the model at defined locations along the drill-string. Several distributed control strategies have been simulated and the induced lateral movement of the drill-string has been analyzed. Simulations were performed with a well configuration from a field case. The first series of simulated experiments were focused on controlling the amount of viscous damping for all subs simultaneously with the same magnitude. It was observed that the effect on the lateral movement in this case was minor. In a second approach, subs placed at different locations had different damping strengths that were varied at specific time steps. Controlling the damping in a distributed fashion had a stronger effect on the local lateral movement and it was possible to create different localized movement patterns along the drill-string.

The concept of utilizing distributed damping subs along the drill-string opens the possibility to actively control the local lateral movement of the drill-pipes and therefore enhance hole cleaning performance. At the same time, torsional oscillations are damped out. Furthermore, the damping subs reduce the overall required torque at the top-drive and facilitate weight transmission to the bit.

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