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doi:10.2204/iodp.proc.334.103.2012

Operations

Two holes were drilled or cored at this site (Table T1). The first hole was drilled with an 8½ inch drill bit with logging-while-drilling (LWD) tools in the BHA to 456.9 mbsf. The next hole was cored with the advanced piston corer (APC)/extended core barrel (XCB) coring system to 523.9 mbsf. The advanced piston corer temperature tool (APCT-3) was deployed four times, and usable data were recovered four times. The Flexit tool was deployed on all 16 piston cores in Hole U1378B. All APC holes were cored with nonmagnetic core barrels. Recovery for Site U1378 was 101.4% with the APC system and 100.3% with the XCB system. Overall core recovery for Site U1378 was 100.5%. A total of 63 cores were recovered after coring 523.9 m. The total length of core recovered at this site was 526.69 m. Hole U1378B was terminated after Core 334-U1378B-63X when hole conditions deteriorated and could not be remediated.

First transit to Site U1378

After an 8.6 h transit from Puntarenas, Costa Rica, covering 94 nmi and averaging 10.8 kt, speed was reduced and thrusters and hydrophones were lowered. Dynamic positioning was initiated over Site U1378 at 1000 h (Universal Time Coordinated [UTC] – 6 h) on 17 March 2011. The position reference was a combination of GPS signals and a single acoustic beacon. The positioning beacon was deployed at 1109 h on 17 March. The beacon was left on site for our return after Site U1379.

Hole U1378A

Rig floor operations commenced at 1000 h on 17 March. The trip to the seafloor was uneventful. The top drive was picked up, the drill string was spaced out, and the LWD hole was spudded at 0425 h on 18 March. After 37.5 h of drilling, Hole U1378A was terminated at 456.9 mbsf. High standpipe pressures, lost circulation, and high torque contributed to the decision to abandon the hole. A wiper trip was attempted, but given the time available versus the progress made to date, the decision was made to terminate Hole U1378A and move to Site U1379 and complete LWD drilling at the second site. After picking up off bottom, the hole was displaced with heavy drilling mud (10.5 ppg) and the drill string was tripped out of the hole to ~640 meters below rig floor (mbrf) while experiencing high torque and significant overpull. The top drive was set back and the drill string was tripped the rest of the way to surface. The 6½ inch drill collars were set back in the derrick. The LWD tools were stored for transit and the rig floor was secured. Thrusters and hydrophones were pulled and the vessel was put into cruise mode, ending Hole U1378A at 0230 h on 20 March.

Second transit to Site U1378

After a 1.25 h transit from Site U1379 covering 6 nmi and averaging 4.8 kt, speed was reduced and thrusters and hydrophones were lowered. Dynamic positioning was initiated over Site U1378 at 1100 h (UTC – 6 h) on 2 April. The position reference was a combination of GPS signals and a single acoustic beacon. On reoccupation of Site U1378, the beacon which had been left on bottom was nonresponsive and declared lost. Another beacon was deployed at 1204 hours on 2 April and was recovered at 2042 h on 6 April.

Hole U1378B

After offsetting the vessel 20 m west, Hole U1378B was spudded at 1515 h on 2 April and advanced with the APC coring system to 127.8 mbsf before refusal. All cores after the fifth core were partial strokes, and the hole was advanced by recovery. The coring system was switched to the XCB, and coring continued from Core 334-U1378B-17X through 63X. Temperature measurements were taken with the APCT-3 on Cores 4H, 7H, 10H, and 13H. Microspheres were run on Cores 20X, 30X, 40X, 50X, and 60X. A total of 16 APC cores were taken with a total recovery of 129.56 m for an overall APC recovery in Hole U1378B of 101.4%. A total of 47 XCB cores were taken over a 396.1 m interval, recovering 396.83 m of core for a XCB recovery of 100.3%.

Coring was terminated after Core 334-U1378B-63X when it became impossible to continue advancing. High top drive torque and lost circulation were major factors. A wiper trip was run to try to clean up the hole, but it was impossible to return to bottom. The hole was terminated, plugged, and then abandoned.

The total cored interval in Hole U1378B was 523.9 m with 526.69 m of core recovered for an APC/XCB combined recovery of 100.5%. The last core on deck for Hole U1378B was at 0035 h on April 6. After trying to condition the hole for 14.5 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 960 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 1850 h and the bit cleared the rotary table at 2030 h. The rig was secured for transit and the beacon was recovered at 2042 h, ending Hole U1378B at 2045 h on 6 April.

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