Longitudinal natural vibration of ultra-long drill string during offshore drilling. (15th May 2018)

• Record Type: Journal Article
• Authors: Wada, Ryota; Kaneko, Tatsuya; Ozaki, Masahiko; Inoue, Tomoya; Senga, Hidetaka
• Is Part Of: Ocean engineering. Volume 156(2018)
• Page Start: 1
• Page End: 13
• Publication Date: 2018-05-15
• Subjects: Ultra-long drill string -- Compensator-induced vibration (CIV) -- Heave compensator -- Longitudinal natural vibration -- Friction; Ocean engineering -- Periodicals; Ocean engineering; Periodicals; 620.4162
• DOI: 10.1016/j.oceaneng.2018.02.054
• Languages: English
• ISSNs: 0029-8018

Abstract

Abstract: Offshore drilling with ultra-long drill strings (i.e., longer than 10, 000 m) creates a new class of technical challenges, such as dynamic variation of weight on bit (WOB). This article investigates observational data obtained from a drilling program conducted by the scientific drilling vessel Chikyu using an 8000 m drill string, which is first of their kind to be recorded. The data exhibited longitudinal oscillation of the drill pipe at frequencies higher than that of heave motion. To identify the cause of such oscillation, one-dimensional dynamic simulation to model drill string's behavior was carried out. The key component of this model is the detailed modeling of the heave compensator. Numerical experiments revealed that longitudinal natural vibration was excited in the ultra-long drill pipe, and the excitation modes corresponded to the behavior of a string with both ends fixed, indicating the possible influence of friction in the heave compensator. We named this class of phenomena compensator-induced vibration (CIV) . In addition, longitudinal elasticity leads to divergence of the tension variation near surface and downhole WOB, which calls for the need to directly measure the downhole WOB behavior. Highlights: High frequency longitudinal vibration observed in 8, 000 m ultra-long drill pipe. Dynamic simulation with detailed modeling of heave compensator's friction successfully reproduced the high frequency signal. Longitudinal natural vibration was excited by stick-slip motion of heave compensator. We named the phenomena CIV, compensator-induced vibration. The difference between variation of top tension and that of downhole WOB will increase as drill string length increases.