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doi:10.2204/iodp.proc.340.108.2013

Operations

Transit to Site U1398

After a 46.0 nmi transit from Site U1397 in cruise mode, the vessel arrived at Site U1398. The vessel stabilized over Site U1398 at 0706 h on 24 March 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 a single acoustic beacon. The positioning beacon was deployed at 0733 h on 24 March. At the end of operations at Site U1398, the beacon was sent an acoustic command to release. The beacon was retrieved at 1420 h on 28 March. The vessel was underway at 1430 h on 28 March to the next site.

Site U1398

Site U1398 consists of two holes (Table T1). The original plan called for two holes to be cored to ~264 mbsf. The first hole was successfully cored and was terminated at a total depth of 268.6 mbsf. The second hole was cored to 263.4 mbsf. Logging was planned for the triple combination (triple combo) and the Formation MicroScanner (FMS)-sonic tools strings, but hole problems forced the cancelation of the logging program during the attempt to run the first logging string. At the end of Hole U1398B, the drill string was pulled back so that the bit was at ~2800 meters below rig floor (mbrf), and the vessel began the 12 nmi transit to the next site in dynamic positioning mode. The advanced piston corer (APC) was deployed 35 times. The cored interval with the APC was 257.0 m with a recovery of 259.09 m of core (101%). The extended core barrel (XCB) was deployed 29 times. The cored interval with the XCB was 275.0 m with a recovery of only 42.75 m of core (16%). Overall recovery for Site U1398 was 57%. Total time spent on Site U1398 was 103.5 h.

Hole U1398A

The vessel arrived at the Site U1398 and was in position at 0706 h on 24 March 2012. Near the end of an uneventful pipe trip, the last 15 stands of pipe had to be measured and drifted. The top drive was then picked up, and the bit was spaced out to spud Hole U1398A. The initial corrected precision depth recorder (PDR) reading was 2944.1 mbrf. The bit was set at 2940 mbrf, and the hole was spudded at 1551 h on 24 March. The seafloor depth was calculated from the length of the first core (2.7 m) to be 2946.8 mbrf (2935.3 mbsl). On the attempt to recover Core 340-U1398A-3H, there was no penetration and no recovery. The XCB was installed for Cores 3X and 4X. After Core 4X, the APC was redeployed. Orientation was performed with the FlexIt tool up to and including Core 7H on all APC cores. Nonmagnetic core barrels were used with the APC for Cores 1H through 7H. After Core 7H, both the FlexIt orientation tool and the nonmagnetic barrels were removed from the coring assembly. Advanced piston corer temperature tool (APCT-3) measurements were taken on Cores 5H through 8H. APC coring continued through Core 13H. At 105.6 mbsf, the APC was removed and an XCB core barrel was dropped. XCB coring continued through Core 30X. Hole U1398A coring was terminated at 268.6 mbsf, after the depth objective was met. Eleven piston cores were taken over 86.3 m with a total recovery of 86.98 m of core. Nineteen XCB cores were taken over a 182.3 m interval. Only 28.11 m (15%) were recovered, and the hole was terminated at 268.6 mbsf. Overall core recovery for Hole U1398A was 43%. After the completion of XCB coring, the drill string was pulled back, the top drive was set back, and the bit cleared the seafloor at 0540 h on 26 March, ending Hole U1398A. Total time spent on Hole U1398A was 46.75 h.

Hole U1398B

After clearing the seafloor from Hole U1398A, the vessel was offset 20 m east, and Hole U1398B was spudded at 0723 h on 26 March 2012. The seafloor depth was calculated from the length of the first core to be 2946.6 mbrf (2935.1 mbsl). Orientation was performed and nonmagnetic core barrels were used through Core 340-U1398B-11H. APCT-3 measurements were taken on Cores 4H, 8H, and 10H. Similar to Hole U1398A, most of the piston cores were partial strokes and the hole was advanced by recovery. After reaching refusal with the APC on Core 24H, the XCB was deployed and XCB coring continued to 263.4 mbsf. Coring was terminated after Core 34X. Twenty-four piston cores were taken over a 170.7 m interval with a total recovery of 172.11 m (101%) of core. Ten XCB cores were taken over a 92.7 m interval. Only 14.64 m (16%) were recovered, and the hole was terminated at 263.4 mbsf. Overall core recovery for Hole U1398B was 71%.

At the conclusion of coring, Hole U1398B was conditioned with a 25 bbl high-viscosity mud sweep and displaced with 133 bbl of 10.5 ppg mud and a go devil was pumped. The drill string was then pulled back to 3016 mbrf, the top drive was set back, knobbies were added to the drill string, the bit was set at 84.91 mbsf, and the pipe was hung from the blocks. The Schlumberger wireline was then rigged up for logging, and the triple combo was deployed. While running in the hole with the triple combo tool string, the drill string became stuck. The tool string was then pulled back to the surface and rigged down. The top drive was picked up, rotation and circulation were reestablished, and the hole was worked vertically until all overpull was eliminated. At this point, because of the poor hole conditions, the nuclear sources were removed from the triple combo tool string. The triple combo was then redeployed but was unable to completely pass through the bottom-hole assembly (BHA), with only a couple of meters of the tool clearing the bit into open hole. After trying unsuccessfully to run the string down, the string was pulled back. At one point the logging tools became stuck, but they were eventually freed and the tools were then pulled back to the surface and rigged down. After laying out the triple combo tool string, we again had to pick up the top drive, and, using rotation and overpull, the drill string was worked free from the formation. The knobbies were then laid out, the top drive was set back, and the drill string was pulled back to 2800 mbrf. The knobbies were then installed, the drill floor was secured, and the acoustic beacon was recovered at 1420 h. At 1430 h on 28 March all activities at Site U1398 were completed, and the vessel then commenced the move to Site U1399 at 1.5 kt. Total time spent on Hole U1398B was 56.75 h.

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