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doi:10.2204/iodp.proc.344.103.2013

Operations

Transit to Site U1381

After a 403 nmi transit from Panama, the vessel stabilized over Site U1381 at 0620 h on 26 October 2012. The initial position was at the coordinates of Hole U1381B (8°25.7149′N, 84°9.4805′W; proposed Site CRIS-1A), which was drilled during Expedition 334 in 2011. The vessel was then repositioned 20 m south of those coordinates. The position reference used for dynamic positioning was a combination of GPS signals, as no positioning beacon was deployed at this site. The final location for Hole U1381C was 8°25.7027′N, 84°9.4800′W, in 2064.6 m water depth.

Hole U1381C

There were three main objectives for Hole U1381C. The first objective was to take a continuous sediment record of the sediment overlying the incoming oceanic crust. The second objective was to capture as much of the sediment/​basement interface as possible. The final objective was to establish a temperature gradient for the sediment section above oceanic crust. Orientation measurements were taken with the FlexIT tool, and formation temperature measurements were taken with the advanced piston corer temperature (APCT-3) tool. Advancement for Hole U1381C was 103.8 meters below seafloor (mbsf), with 103.5 m cored with the APC system and 0.3 m cored with the extended core barrel (XCB) system (Table T1). Recovery with the APC system was 108.7 m (105%), and recovery with the XCB system was 0.33 m (110%).

Rig floor operations commenced at 0620 h on 26 October 2012. The APC/XCB bottom-hole assembly (BHA) was made up with an APC/XCB C-3 bit. The trip to the seafloor was uneventful. The top drive was picked up, the drill string was spaced out, and the hole was eventually spudded at 2015 h on 26 October. The first attempt at spudding Hole U1381C failed when the APC core barrel contacted something unknown inside the seal bore assembly. After trying twice to pressure up and shear, the core barrel was pulled back to the surface and examined. Damage was noted on the leading edge of the cutting shoe, indicating hard contact with something unknown. An XCB core barrel was picked up and pumped down the hole at 50 strokes per minute. This successfully cleared the BHA of whatever was preventing the APC core barrel from landing properly. The APC core barrel was run back into the hole, and the hole was spudded. APC coring continued until ~0730 h on 27 October, when the basement was reached. The APCT-3 was deployed on Cores 344-U1381C-3H and 5H–7H, and four good temperature curves were recorded. The FlexIT orientation tool was deployed on Cores 1H–9H with good results. After reaching basement, the APC system was changed to the XCB system and a single short core was cut to confirm and recover basement material. Last core on deck for Hole U1381C was at 0855 h on 27 October. The hole was then terminated, the top drive was set back, and the drill string was tripped from the hole. The seafloor was cleared at 1020 h, and the BHA was secured on the rig floor at 1545 h, ending Hole U1381C and Site U1381 at 1545 h on 27 October. A total of 33.5 h was spent at Site U1381.

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