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doi:10.2204/iodp.proc.318.109.2011

Operations

Transit to Site U1361

After completing operations at Hole U1359D and attempting to reach the shelf sites (proposed Site WLSHE-12A, Site U1358, or Site U1360), we decided to conduct our final operations at Site U1361. We positioned over Site U1361 at 1945 h on 25 February 2010. The total transit distance from Hole U1359D to near-shelf proposed Site WLSHE-12A and finally to Site U1361 covered 149 nmi at an average speed of 7.1 kt. All times in this section are given in local ship time, which was Universal Time Coordinated + 11 h.

Site U1361

Hole U1361A

We lowered the drill string and started coring Hole U1361A at 0710 h on 26 February 2010. Based on the recovery of the first core, the seafloor depth was 3465.5 meters below rig floor (mbrf) (3454.3 mbsl), or 5.3 m shallower than the corrected precision depth recorder depth. APC coring advanced to 151.5 mbsf and recovered 150.9 m (100%) (Table T1). The first core was obtained with a standard steel core barrel, but all subsequent APC cores were taken with nonmagnetic core barrels. Temperature measurements were made while taking Cores 318-U1361A-4H, 7H, 10H, and 13H at 37.5, 66.0, 94.5, and 123.0 mbsf, respectively.

We switched to XCB coring and deepened the hole from 151.5 to 388.0 mbsf. Cores 318-U1361A-17X through 41X recovered 188.0 m (79%) (Table T1). After Core 41X was recovered at 0120 h on 28 February, we had to suspend coring to deploy a free-fall funnel (FFF) because an iceberg was moving directly toward the site.

We raised the bit to 90 mbsf and deployed a FFF at 0700 h on 28 February. At that time, the iceberg was 5.5 nmi away and continuing to move toward the ship. We waited until ~0900 h to see if it would change course, but it was still heading toward us. At 0945 h, we pulled the bit out of the hole and started moving the ship to the north and out of the iceberg’s path.

The ~500 ft wide iceberg passed directly over the hole at 1245 h. Once the iceberg had cleared the site and was no longer a threat, we moved back over the hole by 1500 h and the reentry camera/sonar system was deployed. At 1555 h, the video failed when the system was 200 m below the ship. When we recovered the camera system we found that water had entered the cable head assembly on the main umbilical cable. As soon as it was repaired we lowered it to the end of the drill string.

We reentered Hole U1361A at 2137 h on 28 February after 15 min of searching and positioning the drill bit over the FFF. We lowered the drill string into the hole as the camera system was retrieved, and by 0130 h on 1 March the bit had reached the bottom of the hole at 388.0 mbsf without having experienced any significant drag while running into the hole. Because of the little time remaining before we had to depart for Hobart, Australia, we decided not to continue coring and prepare the hole for downhole logging.

The hole was flushed with 50 bbl of sepiolite mud and then displaced with 179 bbl of 10.5 ppg heavy mud. The drill string was raised to 88.6 mbsf for logging. We conducted two successful logging runs with the triple combo and the FMS-sonic tool strings, with both reaching the bottom of the hole. Once logging was concluded, the bit was pulled free of the seafloor and the vessel offset 50 m north of Hole U1361A.

Hole U1361B

APC coring in Hole U1361B started at 0840 h on 2 March and established the water depth at 3466.9 mbrf. We only had time for two piston cores before the operational time for the expedition ran out, in part as a result of a delay caused by ice buildup on the APC piston rod. APC Cores 318-U1361B-1H and 2H penetrated to 12.1 mbsf and recovered 12.0 m (100%) (Table T1).

The drill string was recovered and the bottom-hole assembly disassembled into component parts by 2400 on 2 March. We started our transit to Hobart at 0030 h on 3 March. The last line ashore in Hobart was at 1500 h on 8 March.

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