Abstract

The scientific drilling vessel Chikyu was designed to have the capability to drill down to 10,000 m total vertical depth and to obtain core samples. To reach such deep drilling and to recover scientifically worthy core samples, it is important to know the drill pipe dynamics using the actual drilling data for strength evaluation of the drill pipe and for control of a drill bit.

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. During the design phase, strength evaluation of the drill pipe is conducted under several assumptions. To ensure the strength of the drill pipe, it is important to utilize data acquired from actual drilling operations and to verify the analysis model. Furthermore 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.

Thus, the authors have acquired the drilling data including the vessel motions, the hook load variations and the motion of the heave compensator. And analysis with actual drilling data shows the dynamic tension that was actually exerted and the basic performance of the heave compensator. This paper described that the dynamic tension considering influence of the compensator and also the performance of the heave compensator from the viewpoints of following capability including a phase difference. 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.

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