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doi:10.2204/iodp.proc.314315316.134.2009

Operations

Positioning on Site C0006

The D/V Chikyu arrived at Site C0006 on 27 December 2007 and began testing the underwater television system (UWTV). Electronics problems forced cancellation of that test, and positioning over Hole C0006C began at 1200 h on 28 December. The hydraulic piston coring system (HPCS) bottom-hole assembly (BHA) was rigged up and run to the seafloor, and Hole C0006C was tagged at 1915 h on 28 December.

Hole C0006C

Because of the lack of a camera system or remotely operated vehicle (ROV) observation, collection of a mudline core had to be accomplished by trial and error. One HPCS core (316-C0006C-1H) was taken at 1915 h on 28 December 2007 (33°1.6458′N, 136°47.6282′E; seafloor = 3880.5 m mud depth below sea level [MSL]), resulting in full recovery, which required repositioning and reshooting in order to collect the mudline.

Hole C0006D

One HPCS core (316-C0006D-1H) was taken in Hole C0006D (33°1.6431′N, 136°47.6282′E; seafloor = 3877.5 m MSL) at 2245 h on 28 December 2007, resulting in full recovery with no mudline. The vessel was again repositioned.

Hole C0006E

Core 316-C0006E-1H was collected at 0000 h on 29 December 2007, resulting in 5.19 m of recovery, including the mudline in Hole C0006E (33°1.6444′N, 136°47.6282′E; seafloor = 3875.81 m MSL). HPCS coring continued from 5.19 m CSF. We collected 14 HPCS cores with total recovery of 83.54 m (average recovery = 105.31%). Advanced piston coring temperature tool (APCT3) measurements were taken every other core starting at the third core (316-C0006E-3H, 5H, 8H, 10H, 12H, and 14H). Refusal (no penetration) occurred at Core 316-C0006E-14H, and HPCS coring was halted.

Extended shoe coring system (ESCS) coring commenced at that time, resulting in the recovery of 35 cores (316-C0006E-15X through 49X) with total recovery of 330.11 m at a rate of 74.76%. Six Davis-Villinger Temperature Probe (DVTP) measurements were made following Cores 316-C0006E-23X, 26X, 28X, 29X, 35X, and 42X. Three of the DVTP runs were unsuccessful because of battery failure, thermistor failure, and failure to penetrate formation following Cores 316-C0006E-23X, 28X, and 42X, respectively.

After observing a drastically reduced rate of penetration during the cutting of Core 316-C0006E-49X, we determined that refusal had been reached, and Hole C0006E was completed at 409.4 m CSF at 1930 h on 6 January 2008. We killed Hole C0006E with high-density mud, pulled the BHA out of the hole, tripped the drill pipe, and racked back the HPCS/ESCS BHA. During this time, an electrical problem with the wireline winch motor required that Core 316-C0006E-49X be recovered after recovering the BHA on the rig floor. This occurred at 0330 h on 7 January. Table T1 shows the cores collected, meters recovered, and recovery percentage for Holes C0006C, C0006D, and C0006E.

Hole C0006F

The Chikyu then relocated to Hole C0006F and the rotary core barrel (RCB) BHA was run to the seafloor. Hole C0006F (33°1.6242′N, 136°47.6282′E; water depth = 3875.5 m MSL) was tagged at 1730 h on 7 January 2008. We conducted jet-in to 50 mbsf and washed to 395 mbsf. RCB coring operations began, and 23 RCB cores were recovered (Cores 316-C0006F-1R through 23R) from 395 to 603 m CSF with total recovery of 56.48 m at a rate of 27.15%.

Following collection of Core 316-C0006F-23R, it was determined based on pump rates, pressure, torque, and rotations per minute (rpm) that the hole condition had deteriorated to such a degree as to make further coring too risky. As pumping rate increased, the torque increased to the point of stalling the top drive (0 rpm); as pump rates dropped, torque would simultaneously drop and rpm would increase. The only way to get the bit back to the bottom of the hole was to run in the hole with <10 strokes per minute, which was considered unacceptably risky for either drilling or coring. The decision was made at ~0900 h on 13 January to abandon Site C0006 and relocate to proposed Site NT1-03A as an alternative means to achieve the science goals for the NT1-03 family of sites. We killed Hole C0006F with high-density mud, pulled the BHA out of the hole, tripped the drill pipe, and racked back the RCB BHA at 2100 h on 13 January. Table T2 shows the cores collected, meters recovered, and recovery percentage for Hole C0006F.

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