Vibration detection from mud logging systems has revealed that torsional vibration is common in harsh drilling environments, and is a major cause of bit and drillstring failures. Suppressing this type of vibration with an automated vibration detection system, torque feedback, and rigsite vibration suppression guidelines has produced a significant improvement in drilling performance.
In the drilling industry, it is now well established that vibration can cause premature failure of the drillstring and bit. In recent years, this understanding has been extended to identify the relationship between specific modes of vibration and certain types of damage (1,2). In response, various types of monitoring equipment have been developed, and have demonstrated that vibration can often be detected and suppressed (3,4,5,6,7,8,9).
This paper focuses on the detection and suppression of torsional vibration, which appears at surface as regular, periodic cycling of drive system torque. These oscillations usually occur at a frequency close to the fundamental torsional mode of the string, which depends primarily on the drillpipe length and size, and the mass of the bottom hole assembly (BHA). Their amplitude depends upon the nature of the frictional torque down hole, and the properties of the surface drive system. The significance of this behaviour at surface is that it is accompanied by alternating acceleration and deceleration of the bottom hole assembly and bit, and repeated twisting of the more limber drillpipe section.
The most severe form of this vibration produces slip-stick behaviour of the bit and BHA, during which the BHA alternately comes to a complete halt, until twisting of the drillpipe section produces sufficient torque to overcome the resistance to bit/BHA rotation. The BHA then spins free, accelerating to a significantly higher speed than observed at surface, before slowing down again as rotational energy is dissipated.