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doi:10.2204/iodp.proc.314315316.133.2009

Operations

Positioning on Site C0004

The D/V Chikyu arrived at Site C0004 on 19 December 2007. The final site drilled during IODP Expedition 315 was <5 nmi from Site C0004, requiring minimal transit time prior to the start of Expedition 316 operations. Additionally, because the site was occupied during Expedition 314 for both pilot hole (Hole C0004A) and LWD (Hole C0004B) operations, the acoustic beacons required for dynamic positioning (DP) operations were already in place. The first part of the science party arrived on the vessel on 13 December, and by the afternoon of 19 December all were onboard. Hole C0004C was tagged at 0535 h on 20 December at 2632 m drillers depth below rig floor (DRF) (2603.5 m mud depth below sea level [MSL]).

Hole C0004C

Hydraulic piston coring system (HPCS) coring commenced at that time and continued to 89.22 m core depth below seafloor (CSF). Three advanced piston coring temperature tool (APCT3) measurements were taken at the same time Cores 316-C0004C-3H, 6H, and 9H were collected. We changed to the extended shoe coring system (ESCS) at 2213 h on 20 December 2007 and continued to 127.22 m CSF. Because of poor ESCS core quality, we changed back to the HPCS at 0447 h on 21 December and collected three cores (316-C0004C-16H through 18H). The last HPCS core (316-C0004C-18H, 133.18–135.00 m CSF) also included an APCT3 run. At 0732 h on 21 December, because of failure to achieve full penetration using the HPCS, we pulled the bottom-hole assembly (BHA) and drill pipe out of the hole and killed the hole with high-density mud.

Table T1 shows the cores collected, type of coring system, depths, and recovery for Hole C0004C.

Hole C0004D

Repositioning to Hole C0004D began at 1300 h on 21 December 2007, while making up the rotary core barrel (RCB) assembly and running pipe to the seafloor.

We tagged Hole C0004D at 0030 h on 22 December at 2659 m DRF (2630.5 m MSL) and washed to 100 m CSF. We commenced RCB coring at 1225 h on 22 December. During RCB coring, we inferred several instances of plugged bit throat and plugged bit nozzles from coring results and pressure readings and conducted bit deplugging to clear the problem. We used variations in rotations per minute (rpm) and drilling fluid pressure/​flow rate to attempt to improve recovery and cleaned the bit by increasing flow after each core. Additionally, because of recovery problems, short cores (4.5 m) were taken on every coring run below 238 m CSF (Core 316-C0004D-21R).

Coring was delayed several times because of weather conditions, for a total of ~6 h of standby. An additional 3 h of downtime was caused by a fault in the integrated automation system that provides power to one of the DP modules.

Drilling reached TD (400 m CSF) at 2334 h on 25 December. We pulled out of the hole and killed the hole with high-density mud. Then we tripped the drill string and broke down the bit assembly.

We recovered seafloor acoustic navigation beacons, repositioned the vessel to IODP Site C0006, and commenced preparations for testing the underwater television camera (for drilling at depths >3000 m MSL).

Table T2 shows the cores collected, type of coring system, depths, and recovery for Hole C0004D.

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