Deployment operation of NanTroSEIZE C0002 riserless LTBMS

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Author(s): Kyo, N.; Saruhashi, T.; Sawada, I.; Namba, Y.; Kitada, K.; Kimura, T.; Toczko, Sean; Araki, E.; Kopf, A.
Integrated Ocean Drilling Program, Expedition 332 Scientists
Author Affiliation(s): Primary:
JAMSTEC, CDEX, Yokohama, Japan
University of Bremen, Germany
Volume Title: AGU 2011 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2011; American Geophysical Union 2011 fall meeting, San Francisco, CA, Dec. 5-9, 2011. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The installation of LTBMS (Long Term Borehole Monitoring System) for NanTroSEIZE (Nankai Trough Seismogenic Zone Experiment) C0002 riserless hole was successfully carried out as part of IODP Expedition 332 operations by DV Chikyu in November-December 2010. The water depth of the site and penetration depth of the hole are 1937.5 m and 980 mbsf respectively. Casing (9-5/8") was set to the depth of 888 mbsf and below the CORK head, 3-1/2" tubing was deployed inside the casing as the support structure for the downhole instruments. Within the rat hole section, two pressure ports, a strain meter, a tilt meter, a broadband seismometer, geophone, and accelerometer were deployed. These seismic and geodetic sensors were set within the borehole, and coupled to the formation via cement whose physical properties (Young's modulus, Poisson's ratio, density) were adjusted to fit the formation's properties. Screen sections were set to access the pore fluids, while isolating them from the sea floor and the lower lithological units by a swellable packer, and cement, respectively. At the top of wellhead, and at the apex of the 3-1/2" tubing assembly, a CORK head was landed. The CORK head holds the pressure sensor unit (4 pressure sensors), underwater mateable data connectors (connected to the cemented sensors), and hydraulic valves to access and sample formation fluids by ROV. The major scientific features of the Hole C0002G (riserless) LTBMS are sensors monitoring multiple parameters related to seismic, geodetic and pore fluid behavior simultaneously at distinct, multiple, layers within the same borehole. The main technical difficulties in the LTBMS development are as follows: (1) Reduction method for current-induced VIV (Vortex Induced Vibration) (2) Borehole coupling for seismic and geodetic sensors (3) Anti-vibration/shock and protection method for borehole sensors/instruments (4) Attachment and protection for sensor cables and pressure lines (5) Zone isolation for multi-layer pressure measurements (6) Wellhead system (CORK) for data connection to submarine cable network (7) Downsizing borehole instruments (installation with 3-1/2-in tubing) (8) System reliability (redundant sensor system) We carried out sea trials using a dummy sensor assembly to study the effects of deploying the assembly in strong currents, and also carried out additional pool experiments and numerical simulations to evaluate VIV countermeasures. Through shock and vibration mechanical tests, we improved the robustness of sensors and the sensor carrier. As part of these investigations, we conducted risk analysis based on the operation, science, and engineering points of view from, which helped clarify operational procedures for actual deployment. Future plans include returning to Hole C0002G site to deploy a data logger and battery for temporary observations. After examining the data quality, we'll finally connect the LTBMS to the DONET (Dense Oceanfloor Network System for Earthquakes and Tsunamis) submarine cabled network. Plans are also underway for deploying more LTBMS's into Site C0010 (riserless) and Site C0002 (riser).
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Boreholes; Design; Drilling; Expedition 314; Expedition 315; Expedition 332; IODP Site C0002; Instruments; Integrated Ocean Drilling Program; NanTroSEIZE; North Pacific; Northwest Pacific; Pacific Ocean; Seismicity; West Pacific
Coordinates: N331800 N331800 E1363800 E1363800
Record ID: 2012039976
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