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doi:10.2204/iodp.proc.340.109.2013

Operations

Transit to Site U1399

After a leisurely 1.5 kt move over 12 nmi, the vessel stabilized over Hole U1399A with the drill string already deployed to 2800 meters below rig floor (mbrf) at 2215 h on 28 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 2212 h on 28 March. At the end of operations at Site U1399, the beacon was sent an acoustic command to release. The beacon was retrieved at 0740 h on 3 April. The vessel was underway at 1430 h on 4 April to the next site.

Site U1399

Site U1399 consists of three holes (Table T1). The original plan called for two holes to be cored to ~290 meters below seafloor (mbsf). The first hole was successfully cored and was terminated at a total depth of 274.7 mbsf. The second hole was piston cored to a depth of 183.0 mbsf and abandoned when the hole became too unstable to continue coring operations. A dedicated logging hole was then drilled to 240 mbsf to undertake a logging program including the triple combination (triple combo), Versatile Seismic Imager (VSI), and Formation MicroScanner (FMS)-sonic tools strings. At the conclusion of logging in Hole U1399C, the drill string was pulled back and, with 40 stands of drill pipe to go at 0930 h on 3 April 2012, polypropylene rope was found wrapped around the drill pipe. After clearing the drill string of miles of poly line, 28.25 h later at 1415 h on 4 April the bottom-hole assembly (BHA) was finally secured on the rig floor. After the rig floor was secured at 1415 h, ending Hole U1399C, the remaining thrusters were pulled and the vessel proceeded underway to the next site. The advanced piston corer (APC) was deployed 55 times. The interval cored with the APC was 388.0 m with a recovery of 393.49 m of core (101%). The extended core barrel (XCB) was deployed seven times. The interval cored with the XCB was 67.2 m with a recovery of only 9.43 m of core (14%). Overall recovery for Site U1399 was 89%. Total time spent on Site U1399 was 160.00 h.

Hole U1399A

With the drill string already deployed to 2800 mbrf, the knobbies that had been installed for the dynamic positioning move were removed from the drill string. The drill string was then tripped to just above the seafloor. The precision depth recorder (PDR) was then used to approximate the distance below the rig floor, and the top drive was picked up and spaced out to 2908 mbrf. Hole U1399A was spudded at 0145 h on 29 March 2012. The seafloor depth was calculated from the length of the first core (5.1 m) to be 2912.4 mbrf (2900.8 mbsl). The APC was advanced throughout the day and into the following day. APC coring was terminated at 207.5 mbsf on Core 340-U1399A-29H. Core orientation was performed with nonmagnetic core barrels used through Core 12H. Advanced piston corer temperature tool (APCT-3) measurements were taken on Cores 3H through 6H. APC coring was difficult over the entire 207.5 m interval. Sixteen partial strokes were recorded, and three cores had to be drilled over to release them from the formation. The hole was advanced by recovery. After reaching refusal with the APC on Core 29H, the XCB was deployed, and XCB coring continued to 274.7 mbsf. Coring was terminated after Core 36X. Twenty-nine piston cores were taken over a 207.5 m interval with a total recovery of 210.45 m of core (101%). Seven XCB cores were taken over a 67.2 m interval. Only 9.43 m were recovered (14%), and the hole was terminated at 274.7 mbsf. Overall core recovery for Hole U1399A was 80%. The drill string was pulled clear of the seafloor at 2115 h on 30 March, ending Hole U1399A. Total time spent on Hole U1399A was 47.00 h.

Hole U1399B

The vessel was offset ~350 m northeast of Hole U1399A on a line of 050° while maintaining position with the acoustic beacon deployed at Hole U1399A. Because of the fairly large offset from Hole U1399A, a new PDR depth was recorded for Hole U1399B. Using the new PDR depth, the top drive was picked up and spaced out to 2908 mbrf. Hole U1399B was spudded at 2315 h on 30 March 2012. The seafloor depth was calculated from the length of the first core to be 2911.8 mbrf (2900.2 mbsl). Orientation was performed and nonmagnetic core barrels were used up to and including Core 340-U1399B-14H. APCT-3 measurements were taken on Cores 3H, 6H, and 9H. Similar to Hole U1399A, most of the piston cores were partial strokes and the hole was advanced by recovery. Hole problems were encountered after Core 27H while running in and trying to land a core barrel. After the drill string was freed, the bit was pulled back a single joint of pipe at a time until rotation and torque could be reestablished. While drilling back to the bottom of Hole U1399B, fill was encountered 15 m off the total depth. After trying unsuccessfully for >4 h to reestablish coring, a decision was made to abandon Hole U1399B. Coring was terminated after Core 27H. Twenty-six piston cores were taken over a 180.5 m interval with a total recovery of 183.04 m of core. Overall core recovery for Hole U1399B was 101%. There was one drilled interval of 2.5 m. Final depth for Hole U1399B was 183.0 mbsf. The drill string was then pulled back, and the bit cleared the seafloor at 0900 h on 1 April, ending Hole U1399B. After pulling clear of the seafloor, the vessel was repositioned 50 m from Hole U1399A at a direction of 050°. Total time spent on Hole U1399B was 35.75 h.

Hole U1399C

After discussions with science and operations staff, a decision was made to drill a dedicated logging hole. The vessel was repositioned 50 m from Hole U1399A at a direction of 050°. After spacing out and dropping an XCB core barrel, Hole U1399C was spudded at 1115 h on 1 April 2012. An offset depth from Hole U1399A was used for official water depth. Water depth for Hole U1399C was recorded as 2912.4 mbrf (2900.2 mbsl). Drilling continued to 240 mbsf, and the hole was completed at 0045 h on 2 April. After drilling was completed, a 35 bbl sweep was pumped and the XCB core barrel was recovered. The XCB core barrel was found to be twisted off a couple of meters from the cutting shoe. Circulation confirmed that the errant section of core barrel was not still in the bit but had fallen to the bottom of Hole U1399C. The hole was then displaced with 104 bbl of 10.5 ppg mud. The drill string was pulled back to 80.76 mbsf with knobbies installed and hung from the blocks. Because of numerous indications of poor drilling conditions, a modified triple combo tool string (without any radioactive sources) was made up and run to bottom. Bottom was tagged at 234.6 mbsf. Two passes were made, and the triple combo tool string was then pulled from the hole and rigged down. Next the VSI tool string was rigged up and began running in the hole at 1200 h on 2 April. The required protective species watch was started, and, following VSI protocols, the seismic guns were soft started and the experiment was begun. The VSI tool string was run to 231.6 mbsf, and the VSP experiment continued from the bottom of the hole to the just below the end of pipe. The VSI tool string was then pulled to surface and rigged down at ~1930 h. The FMS-sonic tool string was then rigged up and run in the hole to 207.6 mbsf for two passes before being pulled from the hole. After having a little trouble reentering the pipe, the tools were at the surface and rigged down at 0600 h on 3 April. The drill string was pulled back, and with 40 stands of drill pipe to go at 0930 h on 3 April, polypropylene rope was found wrapped around the drill pipe. The rest of the day was spent removing miles of polypropylene rope from the drill string as the pipe was slowly pulled from the hole. At 1415 h on 4 April, the BHA was finally secured on the rig floor. The debris wrapped around the drill pipe included miles of several different types of polypropylene rope, eyes, shackles, swivels, tarps, temporary fencing and other gear. The best guess is that we managed to spool up an uncharted Fish Aggregating Device. When the end of the BHA cleared the rig floor, it was immediately apparent that at some point during the coring/drilling process at Site U1399 we lost the bit. It is pure speculation whether this happened at the end of Hole U1399B or during the drilling process in Hole U1399C. It is very possible that Hole U1399C was drilled without a bit on the end of the BHA. This would explain the relatively slow penetration rates experienced in certain sections of the hole. After the rig floor was secured at 1415 h on 4 April, ending Hole U1399C and Site U1399, the remaining thrusters were pulled and the vessel proceeded underway to the next site in cruise mode.

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