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doi:10.2204/iodp.proc.329.106.2011

Operations

Transit to Site U1368

After an 80.75 h transit from Site U1367, covering 793 nmi and averaging 9.8 kt, a sonar survey was initiated over Site U1368. The survey essentially replicated the lines of the original site survey in order to confirm depths of bottom and hard returns under the seafloor. After the survey was completed at 1515 h, the speed was reduced and thrusters were lowered. Speed was less than expected because one of the propulsion motors was offline and the vessel sailed most of the voyage into headwinds and seas. Dynamic positioning was initiated over Site U1368 at 1545 h on 12 November 2010. The reference position was a combination of GPS signals. No acoustic beacon was deployed, but a beacon remained on standby in the event of a loss of GPS satellite coverage. Whereas automatic input into the dynamic positioning system was not possible because of a system malfunction, it was possible to manually hold the vessel in position to clear the seafloor with the bottom-hole assembly (BHA) if necessary.

All times in this section are given in local ship time unless otherwise noted. For most of the expedition, local time was Universal Time Coordinated – 10 h.

Site U1368

Six holes were drilled or cored at this site (Table T1). The first hole was a washdown hole drilled with the center bit to establish the sediment depth of 13.6 meters below seafloor (mbsf). The next four holes were cored with the advanced piston corer (APC) system. The last hole was drilled and cored with the rotary core barrel (RCB) system to 115.1 mbsf through sediment and into basement. The advanced piston corer temperature tool was not deployed because of the shallow sediment depth. Perfluorocarbon tracer (PFT) was pumped for the entire drilling/coring interval until the last core was on deck. APC system recovery for Site U1368 was 99.8%. RCB system recovery was 27.6%. A total of 23 cores were attempted while coring 173 m. The total length of core recovered at this site was 89.52 m (51.7% recovery).

Hole U1368A

Rig floor operations commenced at 1545 h on 12 November 2010. The trip to the seafloor was uneventful. The top drive was picked up and the drill string was spaced out, and Hole U1368A was spudded at 0130 h on 13 November. The PFT pump was turned on to displace the drill string with the contamination testing fluid. The washdown hole was drilled to determine depth of basement. Mudline was established as 4302.0 meters below rig floor (mbrf) by tagging with the bit. After drilling down, basement was established at 13.6 mbsf. The bit was pulled back above the seafloor, clearing the seafloor at 0200 h and ending Hole U1368A.

Hole U1368B

After clearing the seafloor, the center bit was pulled by wireline, the vessel was offset 20 m west, and the drill string was spaced out to spud Hole U1368B. After making up the first APC core barrel, the core barrel was run to bottom on the wireline and Hole U1368B was spudded at 0330 h on 13 November. Seafloor depth was established at 3750 mbrf with a mudline core. APC coring continued to 16.0 mbsf. Three cores were taken with a total recovery of 15.84 m for an overall recovery in Hole U1368B of 99.0%. After Core 329-U1368B-3H, the bit was tripped back to just above the seafloor, ending Hole U1368B at 0655 h on 13 November. PFT was mixed with the drilling fluid (seawater) and pumped on all cores for contamination testing.

Hole U1368C

Hole U1368C began at 0655 h when the APC assembly cleared the seafloor after completing Hole U1368B. After offsetting the vessel 20 m north, Hole U1368C was spudded at 0730 h on 13 November and advanced with the APC system to 16.3 mbsf before encountering basement. Seafloor was established at 3749.5 mbrf. PFT was mixed with the drilling fluid (seawater) and pumped on all cores for contamination testing. Two cores were taken with a total recovery of 16.34 m for an overall recovery in Hole U1368C of 100.2%. The drill string was tripped to just above the mudline, clearing the seafloor at 0915 h and ending Hole U1368C.

Hole U1368D

Hole U1368D began at 0915 h on 13 November when the APC assembly cleared the seafloor after completing Hole U1368C. After offsetting the vessel 20 m east, Hole U1368D was spudded at 1000 h and advanced with the APC system for two cores to 15.0 mbsf with a 15.04 m recovery (100.3%). Seafloor was established at 3750 mbrf. PFT was mixed with the drilling fluid (seawater) and pumped on all cores for contamination testing. The drill string was tripped to just above the mudline, clearing the seafloor at 1135 h and ending Hole U1368D.

Hole U1368E

Hole U1368E began at 1135 h on 13 November when the APC assembly cleared the seafloor after completing Hole U1368D. The vessel was offset 20 m east of Hole U1368D. After making up the first APC core barrel, the core barrel was run to bottom on the wireline and Hole U1368E was spudded at 1210 h. Seafloor depth was established with a mudline core at 3751.9 mbrf. The APC system was used to take two cores to 10.6 mbsf with 10.58 m recovery (99.8%). PFT was mixed with the drilling fluid (seawater) and pumped on all cores for contamination testing. The drill string was tripped to the surface, clearing the rotary table at 2000 h on 13 November and ending Hole U1368E.

Hole U1368F

After a 20 m offset to the south, Hole U1368F began on 13 November at 2000 h when the bit cleared the rotary table after tripping out of Hole U1368E. The BHA was set back, the APC bit was removed, and the rotary core bit and rotary coring system were assembled in preparation for running the new RCB BHA. The BHA was run into the hole, followed by the drill pipe. After reaching 3741 mbrf, the top drive was picked up and the drill string was spaced out to spud Hole U1368F. Water depth was recorded at 3751.9 mbrf using an offset depth from Hole U1368E. Rotary coring began at the seafloor when Hole U1368F was spudded at 0520 h on 14 November. Core 329-U1368F-2R crossed the sediment/basalt interface at 11.8 mbsf. RCB coring continued from 11.8 to 115.1 mbsf with average recovery. A total of 14 cores were taken, and a total of 115.1 m was cored with a recovery of 31.74 m of core. RCB system recovery for Hole U1368F was 27.6%. PFT was mixed with the drilling fluid (seawater) and pumped on all cores for contamination testing. Microspheres were also deployed on all RCB cores after Core 2R. After reaching a total depth of 115.1 mbsf, the center bit was deployed and the hole was conditioned for logging. The mechanical bit release was activated, dropping the RCB bit at the bottom of the hole. The drill string, minus the bottom half of the mechanical bit release and RCB bit, was tripped to ~30 mbsf and the logging tools were rigged up and deployed. Four logging runs, two with the triple combination (triple combo) and two with the Formation MicroScanner (FMS) tool string (no sonic) were performed successfully. At the end of logging activities, the tools were rigged down and the drill string was tripped back to the rig floor and secured for the 1073 nmi transit to the next site, ending Hole U1368F and Site U1368 at 1233 h on 18 November.

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