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doi:10.2204/iodp.proc.334.105.2012

Operations

Transit to Site U1380

After a move in dynamic positioning mode from Site U1378, the vessel stabilized over Site U1380 at 2130 h (Universal Time Coordinated – 6 h) on 6 April 2011. The position reference was a combination of GPS signals and a single acoustic beacon. The positioning beacon was deployed at 2142 h on 6 April and recovered at 1930 h on 8 April.

Site U1380

A single hole was drilled at this site to a depth of 397.0 mbsf (Table T1) with a 9⅞ inch rotary core barrel (RCB) core bit with the center bit installed. The center bit was pulled and RCB coring began at 397.0 mbsf. Coring continued through Core 334-U1380A-10R to 482.4 mbsf. At that point, it became difficult to circulate and high torque was observed on the top drive. A decision was made to make a wiper trip to remediate the poor hole conditions. It was necessary to pull back from 997.4 to 853.0 meters below rig floor (mbrf) before normal circulation and torque were restored. After attempting to return to bottom from 853.0 mbrf, the bit started taking weight at 920.0 mbrf. High torque and lost circulation made it impossible to return to bottom. At 1500 h, preparations began to abandon Hole U1380A. The core barrel was retrieved and the hole was displaced with 120 bbl of 10.5 ppg mud. Overall core recovery for Site U1380 was 61.6%. Nine cores were recovered after coring 85.4 m. The total length of core recovered at this site was 52.37 m. Hole U1380A was terminated after Core 334-U1380A-10R when hole conditions deteriorated and could not be remediated.

Hole U1380A

Rig floor operations commenced at 2135 h on 6 April 2011. The RCB bottom-hole assembly (BHA) was made up with a Rock Bit International C-4 RCB bit and mechanical bit release. 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 0215 h on 7 April. After 19.5 h of drilling with the center bit installed, the center bit was pulled, and a RCB core barrel was dropped and coring began.

Coring was terminated after Core 334-U1380A-10R when it became impossible to continue advancing. High top drive torque and lost circulation were major factors. A wiper trip was done to try to clean up the hole, but it was impossible to return to bottom and the hole was terminated, plugged, and abandoned.

Total drilled interval was 397.0 m. Total cored interval in Hole U1380A was 85.4 m with 52.37 m of core recovered for an RCB system recovery of 61.3%. Last core on deck for Hole U1380A was at 1005 h on 8 April. After trying to condition the hole for 5.0 h, the decision to abandon the hole was made. The hole was displaced with 10.5 ppg mud, and the drill string was pulled back to 824 mbrf with the top drive in place. The top drive was set back, and the remainder of the drill pipe and BHA were tripped back to the surface. The seafloor was cleared at 1730 h, and the bit cleared the rotary table at 1905 h. The beacon was recovered at 1930 h and the rig was secured for transit at 2000 h, ending Hole U1380A and Site U1380 on 8 April.

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