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doi:10.2204/iodp.proc.331.104.2011

Operations

Arrival at Site C0014

The transit to Site C0014 from Site C0013 was short, as the sites are only 300 m apart. The D/V Chikyu arrived during the afternoon of 15 September 2010 to conduct a seabed survey. The selected area features a live clam colony and some cool diffuse seafloor seeps. The second guide base landed offset from the clam colony and away from any venting areas on what appeared to be very soft seabed. By early morning on 16 September, we were ready to core the first pilot hole (Table T1; Fig. F1).

Hole C0014A

Hole C0014A was spudded 7 m south of the guide base on the morning of 16 September 2010. Fortunately, the remotely operated vehicle (ROV) observed the core barrel drop down from the core bit. Unfortunately, the bit was found to be irretrievable except through a complete pipe trip. Thus ended Hole C0014A after coring to just 4 mbsf.

Hole C0014B

Surface current conditions required about a mile of drifting before spudding Hole C0014B at 1087.5 m drilling depth below seafloor (DSF) on the evening of 16 September 2010, 5 m southwest of Hole C0014A. The first core was a hydraulic piston coring system (HPCS) core shot 3 m above the seabed and advanced fully. The second core was recovered after advancing 6.5 m by wash-down. After four good HPCS cores, the liner of the fifth core showed signs of melting, and it was decided to finish the hole on 17 September.

Hole C0014C

The ROV found a new spudding point 22 m west of the guide base on the morning of 17 September 2010. Hole C0014C was shot with the HPCS to recover the mudline, after which the Chikyu moved 9 m south to find a good location to spud Hole C0014D.

Hole C0014D

Hole C0014D was spudded on 17 September 2010. After another successfully recovered mudline, the second core proved difficult to recover. Pulling up showed that the inner barrel was protruding from the bit, ending Hole C0014D at 16 mbsf.

Hole C0014E

Hole C0014E was spudded on 17 September 2010, <1 m from Hole C0014D, and then drilled to 16 mbsf. Two full-length HPCS cores were recovered, after which coring was stopped at 35 mbsf, as we saw little reason to melt more core liner. As the time was approaching for the crew change in Nago Bay, Japan, we decided we had enough pilot holes at Site C0014 and began to move toward Site C0015 to take a few cores at this contingency site until we needed to move to shore.

Hole C0014F

After returning from the crew change at Nago Bay, we stood by while the R/V Natsushima finished operations in the area. Near midnight on 20 September 2010, we tagged the seafloor at 1088 m DSF and then shot the HPCS 4 m above the seabed at Hole C0014F, 5 m northwest of the guide base. This core was taken as a test of the new aluminum liner, and the hole was abandoned after reaching a depth of 4.2 mbsf.

Hole C0014G

On the morning of 21 September 2010 we finally entered the guide base at Site C0014, intending to shoot three HPCS cores with plastic liners before switching to aluminum liners. The first three HPCS cores took us to 28.2 mbsf with good recovery. The next three cores were shot as HPCS cores with aluminum liners with great success, recovering on average 71% of the cored interval in decidedly undeformed and unmelted liners. By Core 331-C0014G-6H, reaching 50.2 mbsf after a 3 m advance, the HPCS was stopped by a hard formation. We switched to the extended shoe coring system (ESCS) and plastic liners until we encountered soft material again. We ended up alternating between the HPCS and ESCS this way until Core 331-C0014G-12H at 66.7 mbsf.

The ESCS system with plastic liners functioned well, despite indications of temperatures well above 200°C, as the period of no circulation was kept to an absolute minimum.

After Core 331-C0014G-12H, we switched to the extended punch coring system (EPCS). This resulted in generally good recovery for eight cores, reaching 98.2 mbsf with variable recovery (averaging 60%). After Core 331-C0014G-20T, recovery again became erratic and gradually deteriorated after Core 24T. By Core 331-C0014G-27T, the seals of the inner barrel showed signs of melting. This happened again for Cores 331-C0014G-28T and 29T, which also had issues pressuring up before firing. For the final Core 331-C0014G-30X, we switched to the ESCS and changed to heat-resistant O-rings. Recovery was 0.5 m for a 9.5 m advance. We decided that 136.7 mbsf total depth was sufficient to complete the site objectives and left on 24 September to take a couple of cores at Site C0013 before starting casing operations in Hole C0014G.

Casing and capping Hole C0014G

The return to Site C0013 was brief, and the Chikyu returned to Hole C0014G on 24 September 2010, preparing to run 5½ inch casing. The casing shoe entered the guide base on the morning of 25 September, but the casing hanger would not go through the wellhead because of a slight incline of the latter. Unlocking the wellhead let the tool through, and, after a trip to surface, the ROV was able to land the cap on the wellhead on the afternoon of 25 September, completing operations at Site C0014.

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