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doi:10.2204/iodp.proc.329.109.2011

Operations

Transit to Site U1371

After a 51 h transit from Site U1370, covering 499 nmi and averaging 9.8 kt, the speed was reduced and thrusters were lowered. Dynamic positioning was initiated over Site U1371 at 0907 h on 2 December 2010. The position reference 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 sea floor 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 U1371

Eight holes were drilled or cored at Site U1371 (Table T1). The first hole was a washdown hole drilled with the center bit in order to establish the sediment depth of 122.5 mbsf. The entire time on site was plagued by high vessel heave, which hindered the advanced piston corer (APC) coring. The first APC hole at the site came back with a disturbed mudline core and was abandoned. The second attempt at a mudline resulted in an over penetration without securing mudline and was abandoned as well. The following three APC holes were successfully cored to refusal. With the remaining time, an additional two holes were cored for mudline cores. The advanced piston corer temperature tool (APCT-3) was deployed five times in Hole U1371D. Perfluorocarbon tracer (PFT) was pumped from Hole U1371E onward until the last core was on deck. APC system recovery for Site U1371 was 94.9%. A total of 46 cores were attempted while coring 410.0 m. The total length of core recovered at Site U1371 was 389.01 m (94.9% recovery).

Hole U1371A

Rig floor operations commenced at 0907 h on 2 December 2010. The trip to the seafloor was uneventful. The top drive was picked up, the drill string was spaced out, and the hole was spudded at 1845 h on 2 December. The washdown hole was drilled to determine depth of basement. Mudline was established as 5316.0 meters below rig floor (mbrf) using the drill bit–tagged depth. There were no anomalies detected during the washdown to basement. After drilling down, basement was established at 5438.5 mbrf (122.5 mbsf). Total depth of the hole was 5439.5 mbrf after the bit was advanced into basement to verify basement contact. The bit was pulled back above the seafloor, clearing the seafloor at 2350 h on 2 December and ending Hole U1371A.

Hole U1371B

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 U1371B. After making up the first APC core barrel, the core barrel was run to bottom on the wireline and fired from 5310 mbrf. The core barrel came back empty and the bit was repositioned to 5315 mbrf. Hole U1371B was spudded at 0300 h on 3 December. Seafloor depth was established at 5316.4 mbrf (5305.1 mbsl) with a mudline core. Vessel heave during spud-in was ~4 m. The first mudline core was too disturbed for science and the hole was terminated. One core was taken with a total recovery of 8.15 m for an overall recovery in Hole U1371B of 100.6%. After Core 329-U1371B-1H, the vessel moved 20 m north, ending Hole U1371B at 0300 h on 3 December.

Hole U1371C

Hole U1371C began at 0300 h after abandoning Hole U1371B. After offsetting the vessel 20 m north, Hole U1371C was spudded at 0445 h. Core 329-U1371C-1H came back with a full core barrel and no obvious mudline. Shoot depth was 5312 mbrf, which was 3 m higher than the shoot depth for Hole U1371B. The best explanation for another mudline failure was the high heave (>4 m) at the time of spudding. One core was taken in Hole U1371C, with a total recovery of 9.85 m (103.5%). Hole U1371C was abandoned after the first core and the vessel moved 20 m east on 3 December, ending Hole U1371C at 0445 h.

Hole U1371D

Hole U1371D was spudded 20 m east of Hole U1371C at 0635 h on 3 December. Seafloor depth was established with a mudline core at 5311.1 mbrf (5299.9 mbsl). Orientation with the Flexit tool was done on Cores 329-U1371D-1H through 11H. APCT-3 measurements were taken on Cores 4H–6H, 8H, and 10H. All temperature measurements returned good data. While pulling Core 6H, the coring line parted at the wire rope socket and the core barrel and sinker bars fell back inside the drill pipe. The wireline was removed from the hole and reheaded at surface. The aft sinker bars were installed and a rotary core barrel was dropped to “fish” the forward sinker bars. The sinker bars were recovered by wireline, and Core 6H was recovered. Total time from the incident to resumption of coring was 5.5 h. Coring continued until refusal on Core 14H. The APC system was used to take 14 cores to 126.0 mbsf with 126.87 m recovery (100.7%). After Core 14H, the bit was advanced and rotated into basement to verify basement depth. The bit was tripped back to just above the seafloor, ending Hole U1371D at 1330 h on 4 December.

Hole U1371E

Hole U1371E began with the ship offset 20 m east of Hole U1471D. Hole U1371E was spudded at 1605 h on 4 December. Seafloor depth was established with a mudline core at 5310.2 mbrf. The APC system was used to take 14 cores to 128.2 mbsf with a 118.16 m recovery (92.2%). Nonmagnetic core barrels were used for the first 12 cores. PFT was mixed with the drilling fluid (seawater) and pumped on all cores for contamination testing. After Core 329-U1371E-14H, the bit was advanced and rotated into basement to confirm basement depth and tripped back to just above the seafloor, ending Hole U1371E at 1100 h on 4 December.

Hole U1371F

Hole U1371F was offset 20 m south of Hole U1371E. After making up the first APC core barrel, it was run to bottom on the wireline and Hole U1371F was spudded at 1205 h on 5 December. Seafloor depth was established with a mudline core at 5308.3 mbrf. The APC system was used to take 14 cores to 130.6 mbsf with a 118.44 m recovery (90.7%). PFT was mixed with the drilling fluid (seawater) and pumped on all cores for contamination testing. After Core 329-U1371F-14H, the bit was advanced and rotated into basement to verify basement depth and APC advance. The drill string was tripped to just above the seafloor, ending Hole U1371F at 0655 h on 6 December.

Hole U1371G

Hole U1371G was offset 20 m south of Hole U1371F. After making up the first APC core barrel, the core barrel was run to bottom on the wireline and Hole U1371G was spudded at 0755 h on 6 December. Seafloor depth was established with a mudline core at 5314.1 mbrf. The APC system was used to take a single core to 1.4 mbsf with a 1.37 m recovery (97.9%). PFT was mixed with the drilling fluid (seawater) and pumped in for contamination testing. After taking mudline Core 329-U1371G-1H, a second core (test Core 329-U1371G-2H) was taken for training purposes. The drill string was tripped to just above the seafloor, ending Hole U1371G at 0945 h on 6 December.

Hole U1371H

Hole U1371H was offset 20 m west of Hole U1371G. After making up the first APC core barrel, the core barrel was run to bottom on the wireline and Hole U1371H was spudded at 1030 h on 6 December. Seafloor depth was established with a mudline core at 5310.3 mbrf. The APC system was used to take a single core to 6.2 mbsf with a 6.19 m recovery (99.8%). PFT was mixed with the drilling fluid (seawater) and pumped in for contamination testing. After taking mudline Core 329-U1371H-1H, the drill string was tripped to the surface, clearing the rotary table at 2326 h on 6 December. The rig floor was secured for the 1172 nmi transit to Auckland, New Zealand, ending the final hole and site of Expedition 329 at 2326 h on 6 December.

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