Kazuyasu Wada

Effect of Drill-Ship Motions on Core Sample Conditions During the Nankai Trough Seismogenic Zone Experiment

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Stage 1A, which is a part of the Integrated Ocean Drilling Program (IODP), is a series of expeditions in scientific drilling and coring operations aboard the first riser-equipped deep sea drilling vessel, Chikyu. The objectives are to recover good quality core samples and collect data on undersea properties and drilling conditions, which will also provide valuable information for future expeditions. The coring operations were carried out under harsh drilling and ocean conditions so that core recovery was inconsistent and fluctuated from high to low. Moreover, differences in independent lithology, depth, and the type of coring tools from previous expeditions made it necessary to analyze and optimize drilling parameters with new data. A serious concern in retrieving core samples was the vertical heave motions caused by the drill-ship since the active heave compensator system could not be activated before operations due to the extreme deep sea conditions and only the passive heave compensator was used. The drill string and coring tools are particularly vulnerable to the high heaving movements of the vessel so that the core recovery rate and quality are also adversely affected. The present work presents an analysis of geotechnical information, drilling parameters and the drill-ship motions the NanTroSEIZE expedition in order to optimize core conditions and maintain high core recovery.Copyright

Fundamental experiments on motion analysis of deep-water risers for OD21 drilling vessel

The OD21 scientific drilling vessel of JAMSTEC, which is scheduled to be internationally operated from 2006, is planned to equip the 2,500 meters long riser string in the initial stage, and the 4000 meters class in the future. The operations of such deep-water riser strings as more than several thousands meters are still far from enough experiences, and the dynamic motions of the riser suspended from the surface vessel are not well examined. The authors carried out the 1/100 scale model experiments with using the visualization method to analyze the dynamic response of risers, and they obtained basic, but such important characteristics against the actual designs of deep-water risers as the longitudinal dynamic elastic response, the lateral motion induced by the parametric oscillation, and so on.