The integrity of drill string while drilling especially under dynamic conditions plays a very crucial role in efficiency; reaching the target (pay zone) and even economical aspects. Considering the dynamics of drill string one would immediately think of vibrations; particularly torsional vibrations, posed on drill string. In worst cases the phenomenon of stick/slip occurs, in which the bit comes to a full stop and then accelerates uncontrollably. The non-uniform acceleration and deceleration of RPM continues to exist during drilling operation with possible catastrophic consequences. Bringing the bit off the bottom and adjusting the RPM are the conventional approaches which are performed on the surface.
This paper reviews and analyzes the present solution approach as related to drill string torsional prevention measures. Furthermore, a proactive solution would be proposed in contrary to the existing methods to prevent the occurrence of torsional vibration in both vertical and directional wells drilled with top-drive system, which will be performed downhole.
By rotating the drill string at top, it stores energy along itself. At a particular point in time drill string accelerates and rotates in an uncontrollable manner due to act of friction and spiral spring behavior of the drill string. During this process the stored potential energy in drill string is converted to kinetic energy.
The proposed approach entails the use of hydraulic power to prevent storing the potential energy along the drill string. That is, if there is an acceptable maximum level of stored potential energy, conversion into kinetic energy will not happen. By this means, the torsional vibrations are highly mitigated if not eliminated completely.
The proactive solution seeks prevention of a phenomenon (torsional vibrations) which can lead to calamities if not contained. However, efficient drilling and ROP are chief goals of drilling engineers. Also this proactive solution will be done down the hole not on the surface. Hence, more efficient drilling is sought by preventing one of most disastrous incidents.