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doi:10.2204/iodp.proc.339.107.2013

Operations

The vessel departed for Site U1389 (proposed Site GC-11A) at 1730 h on 21 December 2011. The 25 nmi journey from Site U1388 was accomplished in 2.5 h, and the R/V JOIDES Resolution was positioned on the new site by 2000 h.

Four holes were drilled at Site U1389 (Table T1). Hole U1389A was cored using the advanced piston corer (APC) to 97.2 meters below seafloor (mbsf) and then with the extended core barrel (XCB) to 354.9 mbsf. Only one piston core (9.5 m) was taken in Hole U1389B. Hole U1389C was cored with the APC to 95 mbsf and then with the XCB to 350 mbsf. Hole U1389D was cored with the APC to 94 mbsf to provide an additional record of the upper section at the site. Hole U1389E was drilled without coring to 335 mbsf and then cored using the rotary core barrel (RCB) to the depth objective of 990 mbsf. Downhole logging was carried out in Holes U1389A and U1389E using the triple combination (triple combo) and Formation MicroScanner (FMS)-sonic tool strings (see “Downhole logging at Site U1389”). The Versatile Sonic Imager (VSI) tool string was deployed for a vertical seismic profile (VSP) survey in Hole U1389A. Overall recovery at Site U1389 was 307.28 m (103.55% recovery) with the APC, 463.93 m (90.49% recovery) with the XCB, and 352.28 m (53.78% recovery) with the RCB. The total cored interval at Site U1389 was 1463.4 m and total recovery was 1123.49 m (76.8%).

Hole U1389A

The APC/XCB bottom-hole assembly BHA was assembled and deployed to 651.7 mbrf. Subsequent to a 1.3 h survey of the seafloor, Hole U1389A was spudded with the APC at 0240 h on 22 December. The water depth calculated from the recovery of the first core established the seafloor at 656.2 meters below rig floor (mbrf; 644.7 mbsl). This was 1.3 m shallower than the corrected precision depth recorder depth.

Piston coring advanced Hole U1389A to the refusal depth of 99 mbsf. The average recovery for this interval was 103%. Core orientation started with Core 339-U1389A-4H. Three advanced piston corer temperature tool (APCT-3) measurements were made at 33 (Core 4H), 61 (Core 7H), and 90 (Core 10H) mbsf. Nonmagnetic core barrels were utilized on all cores. XCB coring deepened the hole to a final depth of 357 mbsf by 1415 h on 23 December. The average recovery for the 258 m XCB interval of the hole was 91%. The total average recovery for the entire hole was 94%.

Holes U1389B and U1389C

Hole U1389B was spudded at 2010 h, but the full core barrel could not be used to ascertain the seafloor depth. Hole U1389C was spudded with the APC at 2025 h and established the seafloor depth at 654.5 mbrf (643 mbsl). Piston coring advanced to 95 mbsf. Cores were oriented starting with Core 3H. The APCT-3 was deployed at 19 (Core 2H), 47.5 (Core 5H), and 76 (Core 8H) mbsf. All cores were obtained with nonmagnetic core barrels. Coring continued in Hole U1389C with the XCB, which reached the depth objective of 350 mbsf at 0815 h on 26 December. Recovery for the 255 m XCB interval of the hole was 90%. The total recovery for both coring systems for Hole U1389C was 94%. The bit was pulled free of the seafloor at 1000 h on 26 December, and the vessel offset 20 m south of the previous hole.

Hole U1389D

An additional hole was piston cored to obtain a complete section of the uppermost ~100 m portion of the sedimentary record at Site U1389. Hole U1389D was spudded with the APC at 1120 h, and the water depth was established at 655.5 mbrf (644 mbsl). Piston coring advanced without incident to the depth objective of 94 mbsf by 1845 h. Recovery was 104%. The cores were oriented starting with Core 3H. Three APCT-3 measurements were made at 24.5 (Core 3H), 53 (Core 6H), and 75 (Core 9H) mbsf. All cores were obtained with the nonmagnetic core barrels.

Hole U1389E

The drill string was recovered, and the bit cleared the rotary table at 2220 h on 26 December. The vessel offset 20 m west. A four-stand RCB BHA was made up and deployed. After the driller tagged the seafloor at 655 mbrf (643.5 mbsl), Hole U1389E was spudded with the RCB at 0240 h on 27 December. We drilled without coring to 355 mbsf, where continuous rotary coring was initiated at 1830 h. Rotary coring continued until 0845 h on 1 January 2012, when the hole was terminated at the depth objective of 989.9 mbsf. A total of 654.9 m was cored with a recovery of 54%.

Downhole logging at Site U1389

On 23 and 24 December, we carried out downhole logging operations in Hole U1389A. During preparations for logging, the wiper trip found only 1 m of soft fill at the bottom of the hole, and the hole was filled with 112 bbl of 10.5 ppg mud. The open end of the pipe was placed at a logging depth of 85.7 mbsf. The triple combo tool string, composed of the natural gamma radiation (NGR), density, and resistivity tools, descended through the seafloor at 2300 h on 23 December and was run to the bottom of the hole at 1011 mbrf (355 mbsf). A short pass of 75 m was followed by a main pass up to the seabed. Sand-rich layers are apparent by their low gamma radiation signature. The hole was mostly in gauge but had several meter-scale washouts. The tool string was back on deck by 0140 h.

The FMS-sonic tool string reached the bottom of the hole and made two passes, recording resistivity images of the borehole, sonic velocities, and NGR data over the entire interval. The tool string was back on deck at 0950 h. The VSI tool string was run to conduct the VSP experiment. Marine mammal watch started at ~1100 h on 24 December. The air guns (two-gun cluster, 7 mbsl on the port side) were ramped up in a soft start procedure. The VSI tool started its descent in Hole U1389A at 1145 h and reached the bottom of the hole. Ten out of eleven stations recorded good sonic waveforms. Station spacing averaged ~25 m, and the survey itself lasted from 1300 to 1500 h. The tool string was back on deck at 1630 h, and logging equipment was rigged down by 1715 h. At 1755 h, the bit cleared the seafloor and the vessel offset 20 m east of Hole U1389A.

After coring operations had finalized at Hole U1389E, a wiper trip was conducted to condition the hole in preparation for downhole logging. After concluding the wiper trip, the bit was released and the hole was displaced with 375 bbl of 10.5 ppg logging mud. The end of pipe was positioned at 102.2 mbsf. The first log was made with the triple combo tool string, which was deployed shortly after 2400 h on 1 January. The tool was not able to pass a bridge or ledge at 567 mbsf. The tool was recovered at 0610 h after logging the hole up from 567 mbsf. The second logging experiment was made with the FMS-sonic tool string, which was also unable to penetrate deeper than 567 mbsf. The FMS-sonic was recovered at 1425 h after logging the upper portion of the hole.

The VSP experiment was canceled. Shortly after arriving at Site U1389, maintenance was carried out in the vessel’s sea chest and bilge spaces. As part of this routine, ultrasonic thickness readings were taken on the steel plating. Evaluation of the readings indicated that some of the sea chest plating had wastage beyond acceptable limits and that several frames on the starboard side required immediate attention. Although repairs were in progress, it was felt that the sound pressure generated by the air gun during seismic profiling could subject the deteriorated sea chest to sufficiently high levels of vibration that would present a potential risk to the vessel. Therefore, VSP measurements planned for the last three sites of the expedition were canceled. The logging equipment was rigged down, the drill string was recovered, and the beacon was recalled. The vessel departed for the sixth site of the expedition at 1930 h on 2 January. Total time at Site U1389 was 12 days.

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