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doi:10.2204/iodp.proc.322.104.2010

Operations

Hole C0012A

Five transponders were set, and calibration was completed at 0615 h on 25 September. We started running into the hole with a 10⅝ inch coring assembly at 0915 h, spudding Hole C0012A at 2103 h. We jetted to 60 mbsf with the inner barrel, and the seafloor was confirmed at 3539 m drilling depth below rig floor by weight on bit. We continued to jet-in to 60 m drilling depth below seafloor (DSF). Core 322-C0012A-1R was retrieved at 60 m DSF and was on deck at 0020 h on 26 September. The recovered 0.84 m of material was sediments pushed into the core barrel during the jet-in.

Regular rotary core barrel (RCB) coring started from 60 m DSF. Recovered cores were short and of poor quality to Core 322-C0012A-22R because sediments were too soft for RCB coring, but in general, core recovery and quality improved with depth. Ten RCB cores were recovered on 26 September, every 2–2.5 h. See Table T1 for a breakdown of general coring operations. RCB coring continued without any major problems. Reduced pump rate and lower rotation (<30 rotations per minute) were used until Core 322-C0012A-15R (187 m DSF). Average recovery was >80% for Cores 322-C0012A-6R through 11R.

Steady coring operations continued to the end of September, recovering core every 2–3 h except for Cores 322-C0012A-33R and 37R, each of which took >2 h to cut. Every effort was made to optimize the drilling parameters for better core quality. Good quality cores were recovered from Cores 322-C0012A-40R and 45R. On 1 October, core recovery dropped after Core 322-C0012A-47R to <20%, probably due to increased tuffaceous beds. Red silty claystone appeared in addition to hemipelagic mud and tuffaceous beds.

On 2 October, we reached the sediment/basalt interface in Core 322-C0012A-53R. After that, short advances (<5 m) were used to improve recovery of basalt. Coring was suspended after Core 322-C0012A-57R at 560 m DSF, which was the approved maximum penetration depth at this site. Coring resumed at 2045 h after receiving approval for deepening the hole to 600 m DSF.

Core 322-C0012A-58R was on deck at 0100 h on 3 October and became the last core from this hole. Coring was terminated at this point to leave time to complete wireline logging operations before the arrival of an approaching typhoon. Core 322-C0012A-58R was cut by 16 m of advance to reach >30 m below sediment/basalt interface in order to make a space for the logging tool to sit within the basalt interval.

Hole C0012B

Following completion of coring, we started a wiper trip for hole cleaning, during which running back down failed several times at 72 m DSF. Attempts to ream the interval resulted in a probable side track. Efforts were made to return to the original hole, which probably deviated significantly from vertical, but we decided to drill down the side-track hole for wireline logging operations. Although the start of the side track, now Hole C0012B, is unclear, drilling with the center bit was started at 1415 h at 216 m DSF. Target depth was tentatively set at either 600 m DSF or 30 m below the probable sediment/basalt interface.

We stopped drilling at 561 m DSF at 0305 h on 4 October, as drilling parameters suggested this depth was likely to be >30 m below the sediment/basalt interface. We reamed up and down tight spots then drilled another 10 m because we could not clear the fills at the hole bottom. The center bit assembly was pulled out at 2230 h.

Drill bit release was confirmed at 1500 h on 5 October, and the drill string was pulled up to 100 m DSF at 0030 h on 6 October. Rig-up of the wireline logging tools started at 0045 h, and the tools were lowered through the drill pipe. Due to an approaching typhoon, we had <10 h for logging operations. We had only one run with the High-Resolution Laterolog Array (HRLA)–self potential (SP)–slim-Formation MicroScanner (FMS) resistivity image–gamma ray–casing collar locator (CCL). We started running into the hole at 0515 h and observed the seafloor at 3539 m wireline depth below rig floor (WRF) from gamma ray response during the down-logging at 0810 h. We observed a loss of wireline tension and stacking at 3648 m WRF at 0821 h, and we could advance no farther than 10 m into the open hole. After several attempts to pass the difficult interval 10 m below the drill pipe, we cancelled wireline logging operations at 1000 h. The tools were retrieved at 1200 h and rigged down at 1415 h.

Typhoon evacuation and transit

We started moving to south of Hachijo Island for typhoon evacuation at 0245 h on 7 October. We arrived at a safe point near Aoga-shima, 120 nmi southeast of the drilling sites, at 1800 h. Because of high winds and waves, the ship could not hold position in dynamic positioning mode at 2245 h. We continued waiting on weather in autohead mode. After recovery of sea conditions, we started moving to our drilling sites for retrieval of transponders. At 0100 h on 9 October, we attempted communication with a lost transponder at Site C0011, but there was no response. Retrieval of five transponders at Site C0012 was finished at 1410 h. We arrived at Shingu port, and the science party disembarked at 1130 h on 10 October.

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