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doi:10.2204/iodp.proc.340.111.2013

Operations

Transit to Site U1401

After making a 7 nmi dynamic positioning move from Site U1400, the vessel stabilized over the site coordinates for Site U1401 at 1200 h on 13 April 2012. All times reported in this volume are given in ship local time, which was Universal Time Coordinated (UTC) – 4 h. The position reference was a combination of GPS signals and one of two acoustic beacons. The first positioning beacon was deployed at 1755 h on 13 April at the primary site coordinates. The second beacon was deployed 250 m southwest along the crossing seismic line at 1842 h on 14 April. At the end of operations on Site U1401, both beacons were sent acoustic commands to release. Both beacons released on command and were successfully recovered. The vessel began the voyage to Curaçao at 1240 h on 15 April.

Site U1401

Site U1401 consists of four holes (Table T1). This site was originally an alternate site to proposed Site CARI-07C, but it was felt to be a better fit with expedition objectives in the time remaining. The original plan called for two holes to be cored to ~500 meters below seafloor (mbsf). With the limited time remaining, the site was reprogrammed for a single hole to ~350 mbsf. The first hole was terminated at 81.5 mbsf because of unstable hole conditions. It was apparent from the difficult drilling conditions and the time remaining that a new plan was needed. The plan was modified to core a transect on 300 m centers along a seismic line running along a 062°/242° line. In all, four holes were cored at the site. Holes U1401B and U1401C were cored with three piston cores, and a single 9.2 m core was recovered in Hole U1401D before time expired. The advanced piston corer (APC) was deployed 11 times. The cored interval with the APC was 46.7 m with a recovery of 46.43 m of core (99%). The extended core barrel (XCB) was deployed seven times. The cored interval with the XCB system was 67.2 m with a recovery of 1.16 m of core (2%). Overall recovery for Site U1401 was 42%. Total time spent on Site U1401 was 53.00 h.

Hole U1401A

The vessel arrived at Hole U1401A at 1200 h on 13 April 2012 while still tripping drill pipe to bottom. The pipe trip to bottom was without problems, and at 70 stands in, the upper guide horn was pulled and the vibration-isolated television (VIT) camera was installed around the drill pipe. The camera was then run to bottom as the pipe trip continued. At 1610 h, using the subsea camera, we tagged bottom at 2608.5 meters below rig floor (mbrf). After dropping an acoustic positioning beacon, we initiated a bottom survey on a 40 m box to make sure that the area was suitable for spudding Hole U1401A. After spacing out the bit to 1 m above the seafloor, Hole U1401A was spudded at 1950 h on 13 April. APC wireline coring continued through Core 340-U1401A-4H. Every core was a partial stroke of the piston, including the mudline core. Because the mudline core was a partial stroke with a 7.75 m recovery, the official depth used for Hole U1401A was 2608.5 mbrf. The coring system was switched to the XCB for Core 5X, and XCB coring continued through Core 11X at 81.5 mbsf. Hole conditions were abysmal during the entire XCB section of the hole. Recovery was poor, and the hole was terminated at 81.5 mbsf, before the bottom-hole assembly (BHA) became a permanent part of the formation. Four piston cores were taken over a 14.3 m interval with a total recovery of 14.45 m of core (101%). Seven XCB cores were taken over a 67.2 m interval. A total of 1.16 m were recovered (1.7%). Overall core recovery for Hole U1401A was 19%. Hole U1401A took 26.25 h to complete.

Hole U1401B

Given the limited success in trying to core Hole U1401A, we decided to move the ship 300 m in a direction of 242° from Hole U1401A. With the short amount of time remaining and the very difficult coring conditions, a plan was proposed to APC core a transect along one of seismic lines crossing Site U1401. At the location for Hole U1401B, another acoustic beacon was deployed. After recording a new precision depth recorder (PDR) reading for spacing out the drill string, the seafloor was tagged to verify water depth. The bit was then raised 1 m above the seafloor to prevent another broken core barrel. Hole U1401B was spudded at 1620 h on 14 April 2012. Depth was calculated from the tag to be 2618 mbrf. After three partial stroke piston cores, Hole U1401B was terminated; the bit was pulled from the hole and cleared the seafloor at 1940 h, ending Hole U1401B. The total depth of Hole U1401B was 12.9 m, with 12.42 m of core recovered (96%). Hole U1401B took 5.5 h to complete.

Hole U1401C

The ship was then moved 600 m in a direction of 062° from Hole U1401B. At the conclusion of the dynamic positioning move, a new PDR reading was taken for spacing out the drill string. The seafloor was then tagged to verify water depth. The bit was raised 1 m above the seafloor, and Hole U1401C was spudded at 2130 h on 14 April 2012. Depth was calculated from the tag to be 2590.6 mbrf. After three partial stroke piston cores, Hole U1401C was terminated; the bit was pulled from the hole and cleared the seafloor at 2355 h, ending Hole U1401C. Total depth of Hole U1401C was 10.3 m, with 10.44 m of core recovered for an overall recovery percentage of 101%. Hole U1401C took 4.25 h to complete.

Hole U1401D

The ship was then moved 900 m in a direction of 242° from Hole U1401C. At the conclusion of the dynamic positioning move, a new PDR reading was taken for spacing out the drill string. The seafloor was then tagged to verify water depth. The bit was then raised 1 m above the seafloor. Despite manually tagging the seafloor and taking a new PDR reading, the first mudline core came up empty. On the second attempt, Hole U1401D was spudded at 0305 h on 15 April 2012. Depth was calculated to be 2630.4 mbrf. Because operation time had expired, Hole U1401D was terminated after the full stroke mudline core. The drill string was then pulled back to the rig floor. The drill pipe was secured in the pipe racker, and the BHA was disassembled and put away in the drill collar racks. The rig floor was secured at 1230 h on 15 April, ending Hole U1401D and Site U1401. Total depth of Hole U1401D was 9.2 m, with 9.12 m of core recovered (99%). Hole U1401D took 12.5 h to complete.

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