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doi:10.2204/iodp.proc.339.108.2013

Operations

The vessel departed for Site U1390, the sixth site of the expedition, at 1930 h on 2 January 2012. The 22 nmi transit from Site U1389 was covered in just over 2 h. The vessel was positioned on the new coordinates at 2145 h.

Three holes were drilled at Site U1390 (Table T1). Hole U1390A was cored using the advanced piston corer (APC) to 76.7 meters below seafloor (mbsf) and then with the extended core barrel (XCB) to 350 mbsf. Hole U1390B was cored with the APC to 194.1 mbsf. Hole U1390C was cored with the APC to 175.4 mbsf. Downhole logging was carried out in Hole U1390A using the triple combination (triple combo) and Formation MicroScanner (FMS)-sonic tool strings (see “Downhole logging at Site U1390”). Overall recovery at Site U1390 was 437.95 m (98.2%) with the APC and 248.32 m (90.9%) with the XCB. Total cored interval at Site U1390 was 719.5 m and total recovery was 686.27 m (95.4%).

Hole U1390A

The APC/XCB bottom-hole assembly (BHA) and the drill string were deployed with the underwater camera. A survey of the seafloor was conducted using a 30 m grid pattern. Other than one large rock, no significant obstructions were observed. Hole U1390A was spudded with the APC at 0520 h on 3 January. Seafloor depth was established at 1005.1 meters below rig floor (mbrf; 993.4 mbsl), which was 3.1 m deeper than the corrected precision depth recorder value of 1002 mbrf. Piston coring was only able to advance to 76.7 mbsf. The decision was made to switch to the XCB when the last APC core (339-U1390A-9H) required ~3 h to extract from the core barrel. Recovery for the piston-cored interval was 102%. Cores were oriented starting with Core 4H. The advanced piston corer temperature tool (APCT-3) was deployed to measure temperature at 32.1 (Core 4H) and 60.6 (Core 7H) mbsf. XCB coring deepened the hole to the depth objective of 350 mbsf by 1700 h on 4 January. Recovery for the 273.3 m XCB interval was 91%. The overall recovery in Hole U1390A was 93%.

Hole U1390B

With the scientific objective of finding a target horizon on the seismic line at a shallower depth than at Hole U1390A, the vessel was offset 200 m north of Hole U1390A. The underwater camera was deployed and the seafloor monitored during the movement of the vessel. Once the vessel was in position, Hole U1390B was spudded with the APC at 1002 mbrf at 1700 h. The calculated seafloor depth was 1002.4 mbrf (990.7 mbsl). Piston coring advanced to 194.1 mbsf, where Core 21H could not be recovered with the coring line. When the orientation tool was retrieved to the surface using the coring line, it was discovered that the bulkhead lock pin between the male and female sections that connect the nonmagnetic sinker bars to the core barrel had parted in two places (possible metal fatigue). After several fishing attempts failed to grasp the female section that remained downhole with the core barrel, the BHA was recovered and the core barrel extracted at the surface. The bit was at the rotary table at 2120 h on 6 January. Piston coring recovered 189.9 m, which represented 98% of the cored interval. Cores were oriented starting with Core 3H. Temperature measurements were obtained with the APCT-3 at 18.6 (Core 2H), 47.1 (Core 5H), and 75.6 (Core 8H) mbsf. All cores were obtained with nonmagnetic core barrels.

Hole U1390C

The drill string was redeployed for the second time on site and the vessel offset 20 m east of Hole U1390B. Hole U1390C was spudded with the APC at 0240 h on 7 January and established seafloor depth at 1004.1 mbrf (992.4 mbsl). Piston coring proceeded to the depth objective of 174.5 mbsf by 2200 h on 7 January. Stuck core barrels for Cores 2H through 4H required an extra coring line round trip to pull the orientation tool before it was possible to recover the core barrel. Cores were oriented starting with Core 4H and then followed by Cores 9H through 19H (last core). APCT-3 measurements were obtained at 23.4 (Core 3H), 51.9 (Core 6H), 80.4 (Core 9H), and 108.9 (Core 12H) mbsf. Nonmagnetic core barrels were used to obtain all cores. The bit was pulled free of the seafloor at 2300 h and cleared the rotary table at 0115 h on 8 January, ending operations at Site U1390. The vessel departed for the last site of the expedition at 0230 h that morning. Total time on site was 5.2 days.

Downhole logging at Site U1390

Instead of logging the third hole at the site, it was decided to log Hole U1390A. The hole was subjected to routine conditioning procedures, including a wiper trip, mud flushes, and displacement with 124 bbl of 10.5 ppg mud before the bit was placed at 96.6 mbsf. The logging program consisted of the triple combo and FMS-sonic tool strings. The triple combo tool string was deployed at 2400 h on 4 January and recovered at 0330 h. The FMS-sonic tool string was run in at 0600 h and recovered at 1000 h on 5 January. Both tools successfully covered the open hole to 350 mbsf. After the FMS-sonic tool string was rigged down, the bit was pulled clear of the seafloor at 1155 h on 5 January.

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