The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), which is a part of the multinational Integrated Ocean Drilling Program (IODP), is a series of expeditions for drilling and coring operations aboard the world's first riser-equipped scientific deep sea drilling vessel, the (D/V) CHIKYU. The objectives are to recover good quality core samples as well as collect data on undersea properties and drilling conditions, which will also provide valuable information for future expeditions. A serious concern in retrieving core samples was the vertical heave motions caused by the drill-ship since the active heave compensator (AHC) system could not be adjusted in the extreme rough sea conditions before the operations and only the passive heave compensator (PHC) was engaged. The drill string and coring tools are particularly vulnerable to the high heaving movements of the vessel and adversely affect the core recovery rate and quality. The present work presents an analysis of geotechnical information and the drilling parameters such as weight-on-bit (WOB) fluctuations due to the ship heave motions in order to optimize core recovery and improve the drilling equipment.
The deep sea drilling vessel (D/V) CHIKYU (Fig.1) was developed by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) for scientific drilling of the sea floor to recover core samples and analyze them onboard with a team of scientists. The data and information obtained, as part of the multinational Integrated Ocean Drilling Program (IODP), are to advance studies of the deep biosphere, understand the mechanisms behind environmental change, and solid earth cycle. CHIKYU was delivered to JAMSTEC in July 2005 and shakedown, training, and System Integration Tests (SITs) were initiated shortly thereafter (Kyo et al. 2007). Scientific drilling operations for the IODP project began in Sept. 2007 as the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE).