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doi:10.2204/iodp.proc.331.103.2011

Operations

Arrival at Site C0013

The D/V Chikyu arrived at Site C0013 (Table T1) during the night of 8 September 2010, drifted the last mile, and set azimuth thrusters. The ship switched to dynamic positioning mode during the early hours of 9 September and sent the remotely operated vehicle (ROV) down to set five transponders. After the transponders were calibrated, we conducted a seabed survey with the ROV and picked the spot for the hard seabed guide base (27°47.831′N, 126°57.799′E) (Fig. F2). The ship repositioned, the guide base was lowered to the seabed, and the ROV locked the well head into a vertical position.

Hole C0013A

After the seabed survey, on 10 September 2010 the decision was made to core a few pilot holes with the hydraulic piston coring system (HPCS) before committing to the main hole in the guide base. A perfluoromethylcyclohexane (PFC) contamination tracer was added to the active mud tank, and we decided to use microbeads with every HPCS and extended punch coring system (EPCS)/extended shoe coring system (ESCS) core. A plan to sample the drill mud from the active tank every 12 h was enacted.

The first coring attempt was 11 m east of the guide base (Fig. F2). The first run down to the seabed used the advanced piston corer temperature tool (APCT3) shoe, taking a temperature measurement just above the seabed. Following that, however, the HPCS did not fire when the mud pump rate was increased. The core barrel was pulled back up, reassembled, and sent back down. When it arrived at the seabed, we saw that the coring shoe was not protruding from the drill bit as it is designed to do. Before any action could be taken, the pins sheared and we watched the inner barrel slide to the seabed. We attempted to use slow pumping to push the inner barrel into the seabed in order to get core, but the inner barrel bent at the 8.5 m marker and snapped off. The bent and broken barrel required a full pipe trip to recover, leaving the lower half of the core barrel and the APCT3 tool on the seabed. Thus ended Hole C0013A.

Hole C0013B

On 10 September 2010, immediately following Hole C0013A operations, the ship offset 2 m south and tripped the HPCS/ESCS/EPCS coring assembly to the seafloor. The EPCS inner barrel was dropped to the bit this time, cutting the first and only core in Hole C0013B (Fig. F2). As the core was pulled back up to surface, the bit inadvertently pulled out of the hole, ending Hole C0013B.

Hole C0013C

Hole C0013C was spudded with the HPCS on 11 September 2010, 5 m south of Hole C0013B (Fig. F2). When the inner barrel was recovered, the liner was stuck in the barrel and the core had to be pumped out. This was only partially successful. The drill bit again pulled out of the hole, so the ship offset once more to drill Hole C0013D.

Hole C0013D

Hole C0013D was spudded on 11 September 2010, 2 m north of Hole C0013C (Fig. F2). After drilling to 3 mbsf so the bit would stay in the seabed, the first HPCS core recovered 95% of a 9.5 m advance. More than 200 ppm H₂S was venting from the coring shoe, dispersing quickly to 98 ppm by the time the shoe was off. Core 331-C0013D-2H was shot using the HPCS and successfully recovered. The barrel came up too hot to touch, and the liner showed signs of melting; recovery on this attempt was only 15% of a 9.5 m advance. (The acrylide plastic becomes soft at 82°C at surface pressure conditions, as shown by a simple test done by Center for Deep Earth Exploration [CDEX] engineers; data not shown.) We switched to the EPCS to get through what seemed to be a hard layer that reduced HPCS recovery. A 4 m advance using the EPCS recovered 20% sediment. A subsequent switch to the ESCS gave only 1% recovery and a melted liner, so Hole C0013D was abandoned after reaching 35.5 mbsf.

Hole C0013E

Hole C0013E was cored in the guide base at 27°47.4157′N, 126°53.8546′E on 12 September 2010 (Fig. F2). An 8.5 m advance below seafloor produced 6.08 m of very gassy (burp!) core. To avoid melting the core liner, we tried shooting Core 331-C0013E-2H as HPCS without any liner at all. Recovery was 1.21 m from what may have been a 5.5 m advance, with no indication of the system actually firing. Sediment was pumped out into plastic half-liners on the rig floor.

Switching to the ESCS for Core 331-C0013E-3X resulted in just 17 cm of sediment in the coring shoe and an empty liner after a 3 m advance. The situation was similar for Core 331-C0013E-4X; a 3.3 m advance gave only 10 cm of sediment in the coring shoe. Because the first attempt at HPCS coring without a liner misfired and failed, Core 331-C0013E-5H was taken liner-free with the HPCS. A 7 m advance gave 1.29 m of core, which blew out of the barrel when it was extruded hydraulically. We switched back to the ESCS in an attempt to improve core recovery, but Core 331-C0013E-6X came back with only 49 cm of hard sediment in the core catcher.

Core 331-C0013E-7L was taken on 13 September and was the first test of the Baker Hughes INTEQ (BHI) coring system. Using the BHI system requires a bottom-hole assembly (BHA) change and a pipe trip between each core, so this decision was made with a significant level of angst. All other coring methods had met their limit, however, either because of formation hardness or the high temperatures encountered. A 9.2 m advance with the BHI system required ~18 h operational time and yielded only 2.1 m core, suggesting the formation was still too soft for coring with a diamond-impregnated bit. We therefore switched to the ESCS, but we cored 9.8 m without recovery; poor recovery was likely due to a microbead bag blocking a valve. Thus, the decision was made to stop using microbeads for the ESCS core barrel to avoid further core loss. The last core from Hole C0013E, Core 331-C0013E-9X, recovered only 0.25 m sediment from a 9.5 m ESCS advance, as well as some completely melted core liner. As all indications pointed to the fact that hot fluids were welling up the hole, we decided to end Hole C0013E at the penetrated depth of 54.5 mbsf.

Casing and capping of Hole C0013E

At midday on 14 September 2010, the Chikyu moved to a nearby low-current area and prepared to drift and lower five joints of 5½ inch casing into Hole C0013E. The casing run started by evening, drifting the 9 nmi to Hole C0013E at 0.2–1.0 kt, with the casing lowered to 690 m drilling depth below seafloor (DSF). The hole was reentered on the morning of 15 September, and the casing was successfully hung from the guide base shortly after. By early afternoon, the ROV had landed the corrosion cap and we could observe vigorous fluid flow from the central stainless steel pipe mounted in the cap. It was time to move on to the next site (whew!).

Hole C0013F

We returned to Site C0013 on 24 September 2010, after completing coring at Hole C0014G. The second visit was an attempt to collect cores using the aluminum liners that would survive the high temperatures at this site, which we obtained in Okinawa on 19 September. We had only three aluminum liners left at this point, having used the rest earlier in the month at Site C0014. The first core was shot 10 m southeast of the guide base, near Hole C0013C (Fig. F2). The HPCS assembly was fired 2 m above seafloor, advancing 7.5 m into the sediment.

Hole C0013G

After good recovery in Hole C0013F, the Chikyu moved to 10 m south of the guide base for Hole C0013G on 24 September 2010 (Fig. F2). We washed down to 7.5 mbsf in Hole C0013G and shot with the HPCS. We only advanced 1.8 m, to 9.3 mbsf, but with full recovery.

Hole C0013H

Hole C0013H was spudded on 24 September 2010. High pressure was needed to fire the HPCS in the previous hole, so we picked up to above the seabed and circulated before entering Hole C0013H 2 m east of Hole C0013G (Fig. F2). Hole C0013H was washed down to 9.3 mbsf, where the HPCS was fired. Very high pressure was again needed before the shot went off, but we only advanced 0.6 m. Core recovery was 100%.

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