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doi:10.2204/iodp.proc.314315316.135.2009

Operations

Positioning on Site C0007

The D/V Chikyu relocated to Site C0007 (proposed Site NT1-03A) on 13 January 2008. The remotely operated vehicle (ROV) was launched in order to deploy seafloor transponders below the Kuroshio Current (running at 2.0–2.5 kt at the time), the ROV was recovered, and the hydraulic piston coring system (HPCS)/​extended shoe coring system (ESCS) bottom-hole assembly (BHA) was rigged up and readied while the vessel was calibrating for dynamic positioning system navigation and positioning over the site. The BHA was run to the seafloor, and Hole C0007A (33°01.23258′N, 136°47.94852′E; water depth = 4081 m mud depth below sea level [MSL]) was tagged at 2230 h on 14 January.

Holes C0007A, C0007B, and C0007C

The first core (316-C0007A-1H) was a successful mudline core that penetrated to 3.14 m CSF with 100% recovery. Because of operational and curatorial issues, the following core was labeled Core 316-C0007B-1H. This core was taken from 3.14 m CSF and it recovered 10.06 m of sediment with 105.9% recovery. Because the bit came out of the borehole during recovery of this core and no set standard for hole naming dealt with this issue, the following core was labeled Core 316-C0007C-1H. This core was taken from 12.64 m CSF and recovered 7.95 m of sediment with 100% recovery. All further coring was conducted continuously in Hole C0007C from this point. Cores 316-C0007C-2H through 4H, 5X through 15X, and 16H through 18H were collected with a total recovery of 59.31 m at a rate of 36.29% in interlayered silt, sand, and coarse pebbles. The piston core barrel jammed during collection of Core 316-C0007C-18H at ~1500 h on 17 January 2008, requiring several hours of operational down time and resulting in abandonment of Hole C0007C. The inner core barrel was lost during attempts to recover Core 316-C0007C-18H.

The BHA was pulled out of the hole and recovered between 1200 and 2400 h on 18 January. During this operation, a request was made for permission to drill an alternate hole 185 m northwest of Hole C0007C and permission was granted via the Center for Deep Earth Exploration (CDEX) and the Environmental Protection and Safety Panel (EPSP). Because of consideration of the science target and time requirements, the decision was made to run the rotary core barrel (RCB) coring system. Table T1 shows the cores collected, meters recovered, and recovery percentage for Holes C0007A, C0007B, and C0007C.

Hole C0007D

After permission to core at Hole C0007D was granted, the vessel was repositioned 185 m northwest of Hole C0007C. The RCB BHA was made up and run in the hole, and Hole C0007D (33°1.3167′N, 136°47.8872′E; water depth = 4049 m MSL) was spudded at 0330 h on 19 January 2008. Jet-in and wash to 18.0 m CSF and drilling to 175.0 m CSF were conducted to the first coring point, which was reached at 1330 h on 19 January. Coring operations in Hole C0007D resulted in the collection of Cores 316-C0007D-1R through 35R (175.0–493.5 m CSF) with total recovery of 87.9 m at a rate of 27.61%. A combination of

• Determination that the primary scientific target had been reached,
• Deteriorating hole conditions,
• Repeated zero-recovery cores, and
• Recovery of small amounts of loose fine sand in the final core (316-C0007D-35R)

resulted in the determination (made at 1500 h on 24 January) to pull out of the hole, kill the hole with dense mud, and recover the BHA to the surface. The BHA was recovered at 0130 h on 25 January. All sea bottom acoustic navigation beacons were recovered from Sites C0006 and C0007, and the vessel moved to Site C0008 (contingency Site NT2-10) on 26 January. Table T2 shows the cores collected, meters recovered, and recovery percentage for Hole C0007D.

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