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doi:10.2204/iodp.proc.330.108.2012

Operations

The 392 nmi transit to Site U1377 was made without incident at an average speed of 11.2 kt. By 0930 h on 5 February 2011 the vessel was positioning on the coordinates of Hole U1377A (all times are New Zealand Daylight Time, Universal Time Coordinated [UTC] + 13 h). The vibration-isolated television (VIT) frame was launched after a three-stand rotary core barrel drilling assembly was made up with a new Type C-4 bit and a refurbished mechanical bit release and deployed to 988 meters below rig floor (mbrf).

Tagging of the seafloor at 1262.0 mbrf (1250.8 meters below sea level [mbsl]) was observed at 1435 h. The seabed appeared to be covered mostly by a fine layer of sediment and a few scattered rocks (Table T1). After the VIT frame was recovered and the top drive was picked up, Hole U1377A was spudded at 1510 h. Rotary coring advanced amid increasingly difficult hole conditions and overall poor recovery. Finally, after coring to a depth of 53.3 mbsf, the hole became too unstable and had to be abandoned. The bit cleared the seafloor at 1815 h on 6 February and was picked up to 1103 mbrf. Average recovery for Hole U1377A was 16.4%. The time expended on Hole U1377A was 12.5 h.

It was decided to offset the vessel ~500 m south of Hole U1377A and attempt to spud another hole at this site. The vessel was positioned after a 30 min offset with the bit 159 m above the seafloor. The VIT frame was deployed and showed a seafloor covered with soft sediment. The driller tagged the seafloor at 1250.8 mbsl. Hole U1377B was spudded at 2325 h on 6 February, and rotary coring advanced to 18.1 mbsf. During the retrieval of the core barrel for Core 330-U1377B-2R, unstable parts of the formation fell into the hole and were subsequently recovered in the core barrel of Core 330-U1377B-3G. Because the recovered material cannot be assigned to a specific depth, this core was curated as a “ghost” core, as indicated by the suffix “G” in the core name. Below 18.1 mbsf the formation was stable enough to allow drilling to advance to a final depth of 37.0 mbsf, when the allocated time on site expired. As the last core barrel was being retrieved, the coring line was coated with a rust inhibitor in accordance with routine. After the drill string and beacon were recovered and the rig floor was secured for transit, the vessel departed Site U1377 for Auckland, New Zealand, at 0730 h on 8 February. The time on Hole U1377B was 57.5 h, and the total time on site was 70.0 h (2.9 days). Because of concerns of moderate headwinds and rough seas on the transit to Auckland, the vessel departed approximately 18 h earlier than originally planned.

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