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doi:10.2204/iodp.pr.322.2009

Operations

Transit

The Chikyu departed the port of Yokkaichi at 1600 h on 4 September 2009. After ~130 nmi of transit, Chikyu arrived at drill Site C0011 at 1100 h on 5 September. We carried out underwater television (UWTV) free fall for torsion release and spaced out the inner barrel assembly.

Hole C0011B

We started running into the hole with a 10 inch RCB BHA at 2230 h on 5 September 2009 and spudded Hole C0011B at 1700 h on 6 September. We reached 4417 m drilling depth below rig floor (DRF) (340 m drilling depth below seafloor [DSF]) at 1945 h on 7 September. The center bit assembly was retrieved. RCB coring highlights follow:

• Core 1R: the core (2.2 m long) was heavily disturbed because of a twisted core liner. We waited on weather (WOW) for 8 h because of high winds (>20 m/s). Before resuming RCB coring, SET-P and UWTV test runs were carried out.
• Cores 2R–12R: recovered smoothly.
• Core 13R: core line winch cable was tangled during retrieval.
• Core 15R: cut from 4546.5 m DRF but ROP decreased at 4553.8 m DRF. Core jamming was suspected. The core was retrieved after four attempts to latch the inner barrel.
• Cores 16R–20R: short advancements because of slow ROP or unsteady pump rate between 4553.8 and 4578.5 m DRF.
• Cores 21R–27R: relatively steady and good core recovery.
• Core 28R: ROP dropped and abnormal pressure observed at 4649.7 m DRF.
• Core 29R: recovered only 0.3 m of fragments in the core catcher. The center bit assembly was dropped for cleaning inside the pipe and bit.
• Cores 30R–39R: relatively good core recovery.
• Core 40R: hit a hard layer; recovered 4.92 m from an advance of 6.5 m.
• Core 41R: cored 2.0 m to the target depth of SET-P deployment; contained 0.25 m of calcareous concretion in the core catcher and several pebbles of hard mudstone at the bottom of the core.
• Downhole measurement using the SET-P was planned at 680.5 m DSF, targeting a sandy layer identified in the LWD log. The lithology of Cores 40R and 41R turned out to be inadequate for the SET-P experiment.
• Core 42R: short (4.5 m) advance recovered 3.64 m of softer mudstone. As we were without good correlation between LWD and MSCL data to determine depth, it was unclear whether we had overshot the target sand layer or were still above it.
• Core 43R: we continued to attempt to identify a key bed for SET-P tool deployment by taking another short (4 m) core, which recovered 8.49 m (>200% recovery). At first the lithology looked like a thick sand layer sandwiched by mudstone; however the bed turned out to be exotic material such as drill cuttings/debris at the hole bottom.
• Having spent more than the 12 h allocated to the SET-P experiment in our operations plan, we canceled the SET-P tool deployment. We canceled the second run planned at ~900 mbsf as well because the deployment would be more difficult in deeper sections.
• Core 46R: recovered 1.79 m from 3.5 m of advance.
• Cores 47R: core quality was not good because of rough sea state.
• Core 48R: contained rounded pebble-sized mudstone, suspected to be caving/cuttings material.
• Core 49R: damaged and jammed in the inner barrel.
• Core 50R: cleaned the bit and hole and pulled the drill bit up to ~50 m DSF to WOW because of average wind speeds of >18 m/s.
• Core 51R: cored from 757 m DSF.
• Cores 53R–55R: short advancement because of slow penetration. After Core 55R, we drilled with a center bit assembly from 4863.3 to 4921 m DRF (57.7 m).
• Cores 56R–59R: recovered in relatively good condition.
• Core 60R: recovered 0.15 m of material from a short advance of 2.0 m because of low ROP. We decided to wash down several more tens of meters after recovery of the next core.
• Core 61R: took ~10 h to cut and retrieve, even with 5.0 m of advance, and recovered only 5 cm of material.

We decided to finish operations at this site and to move to the next site. Kill mud (100 m³ of 1.3 sg) was spotted, and we started pulling out of the hole at 1730 h on 23 September. TD of Hole C0011B was 4958.0 m DRF (881.0 m DSF). Retrieval of the transponders started in the morning of 24 September and finished before 1830 h. The ship moved to the proposed Site NT1-01A and set transponders.

Holes C0012A and C0012B

Five transponders were set and calibration was completed at 0615 h on 25 September. We started running into the hole with a 10 inch coring assembly at 0915 h, spudding-in Hole C0012A at 2103 h. We jetted down to 60 mbsf with the inner barrel, and the seafloor was confirmed at 3539 m DRF by weight on bit. We continued to jet-in to 60 m DSF. Core 311-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 jet-in.

Regular RCB coring started from 60 m DSF. Recovered cores were short and of poor quality at first because sediments were too soft for RCB coring, but recovery and quality improved with depth. Ten RCB cores were recovered on 26 September, every 2–2.5 h.

RCB coring continued without any major problems. Reduced pump rates and lower rotation (<30 rpm) were used until Core 322-C0012A-15R (187 m DSF). Average recovery was >80% for Cores 6R–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 40R–45R. On 1 October core recovery dropped after Core 47R to <20%, probably due to increased tuffaceous beds.

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 57R at 560 m DSF, which was the approved depth of maximum penetration at this site. Coring resumed after receiving approval to deepen the hole to 600 m DSF.

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

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, 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 center bit was started at 1415 h on 3 October 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, as drilling parameters suggested this depth was likely to be at least 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 hole bottom. The center bit assembly was pulled out at 2230 h on 4 October.

Drill bit release was confirmed, and the drill string was pulled up to 100 m DSF. Rig-up of the wireline logging tools started at 0045 h on 6 October, 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 (GR)–casing collar locator (CCL) tool string. 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 down-logging at 0810 h. We observed a loss of wireline tension and stacking at 3648 m WRF and 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. 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 keep position in dynamic positioning mode; we continued WOW in auto-head 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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