Considerations on of Drillpipe Dynamics with Actual Drilling Data

The scientific drilling vessel CHIKYU was designed to have the capability to drill down to 10000m total vertical depth and to obtain core samples. To reach such deep drilling and to recover core samples, it is important to know drill pipe dynamics using the actual drilling data. The core recovery rate is affected by the variation of the weight on bit caused by the propagation of the vessel heave motions. Therefore, a heave-compensating system will be used and it is very important to evaluate the performance. Furthermore, the drill bit behavior will also influence on the core recovery. In the extreme case, stick-slip, which will cause cracks or fractures in the core samples, occurs. In addition, to reach such deep drilling, a fine strength evaluation is mandatory because there is little margin. So, the estimation of dynamic tension due to vessel heave motions is necessary. Thus, the authors have acquired the drilling data including the vessel motions, the hook load variations and drilling torque variations. It is observed that the heave compensating system have the capability to mitigate the propagation of the vessel heave to the drill string within 30% if the condition is good. On the other hand, it was also observed that the heave compensator operated at a low level of mitigation if the condition is bad. Also we conduct the drill pipe dynamics analysis such as the vertical dynamic motions and the drill bit rotation, and make considerations on the hook load variations and the drill bit behaviors. Actual drilling data provided the worthy information on the drill pipe dynamics. The considerations will be utilized for future operations such as Tohoku Earthquake Drilling Program and NANKAI Trough drilling programs and also for future technical development.