Yuichi Shinmoto

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

A Case Study on Downhole Measurement to Monitor Drilling Hazards in Integrated Ocean Drilling Program (IODP) Expedition 314

For integrated ocean drilling program (IODP) expedition 314, the deep sea drilling vessel Chikyu spent 56 days carrying out scientific drilling in the Kumano basin off the Kii peninsula. Drilling conditions were generally severe through the work of the expedition. In addition to Chikyu on-board measurement system, a state-of-the-art measurement while drilling (MWD) technology primarily intended for monitoring drilling condition such as borehole pore fluid pressure, rotary speed of the drill string. This study demonstrates the downhole measurement using MWD is effective for monitoring occurrence of drilling hazards in Nankai Trough seismogenic zone.

Drilling Experiences of the deep sea drilling vessel CHIKYU in High Current

Deep sea drilling vessel Chikyu is the first riser equipped scientific drilling vessel in the world. Chikyu started the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) from September 2007. The speed of current encountered with Chikyu has been frequently measured more than 4.0 kt throughout NanTroSEIZE. So far, Chikyu carried out drilling operations. In this report, summaries of experiences and findings associated with high current in drilling operations of Chikyu are described.