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doi:10.2204/iodp.proc.303306.105.2006

Operations

Transit from Site U1304 to Site U1305

We departed Site U1304 at 1230 h on 14 October 2004. The 577 nmi transit to Site U1305 (LAB6A) was accomplished in 2.3 days at an average speed of 10.4 kt. We arrived at the Site U1305 and were positioned on location at 2015 h on 16 October.

Hole U1305A

Following routine deployment of the drill string, the driller positioned the bit at 3473.4 meters below rig floor (mbrf) (8 m shallower than the calculated precision depth recorder depth of 3481.4 mbrf). Hole U1305A was initiated with the advanced piston corer (APC) at 0600 h on 17 October 2004. The recovery of the initial core was 8.87 m, suggesting a seafloor depth of 3474.0 mbrf; however, correlation to previous piston cores indicated that the upper part of the sediment section had not been recovered. Piston coring advanced to a total depth of 280.0 mbsf with an average recovery of 105.2%. Recovery percentages were affected by gas expansion at this site (see “Geochemistry”). Use of nonmagnetic core barrels and orientation tools are indicated in Table T1. Cores 29H and 30H were advanced by recovery, and six cores had to be obtained by drillover (Cores 20H, 24H, and 26H–29H). Hole U1305A concluded when the bit cleared the seafloor at 1645 h on 17 October.

Hole U1305B

The ship was offset 30 m east of Hole U1305A. To obtain a mudline core and recover the uppermost part of the sedimentary section, the bit was positioned 4.5 m shallower than at Hole U1305A. Hole U1305B was spudded at 1945 h on 18 October 2004, recovering 8.25 m, which suggested a seafloor depth of 3459.2 meters below sea level (mbsl) (3470.1 mbrf). Piston coring advanced to a total depth of 264.8 mbsf with an average recovery of 103.6% (Table T1). A partial stroke of the APC occurred while obtaining Core 27H, and only two core barrels had to be drilled over (Cores 25H and 28H). Hole U1305A operations concluded when the bit cleared the seafloor at 0215 h on 20 October.

Hole U1305C

After offsetting 20 m east of Hole U1305B, Hole U1305C was spudded at 0400 h on 20 October 2004. Based on recovery of the first core and bit depth, the seafloor depth was calculated to be 3458.8 mbsl (3469.7 mbrf). Piston coring advanced to a final depth of 287.1 mbsf with an average recovery of 103.9% (Table T1). One core was obtained during a partial stroke (Core 19H), which was advanced by recovery. Four other cores were partially stroked (Cores 28H–31H), as indicated by the failure of the corer to completely bleed off pressure. However, these four were not advanced by recovery because each of the core barrels were full. No core barrels required drillover in Hole U1305C.

After completing coring operations, Hole U1305C was displaced with sepiolite mud and the drill string was retracted to 95 mbsf in preparation for logging. The triple combination (triple combo) tool string was deployed to within ~29 m of the bottom of the hole (287 mbsf). The 163 m of open hole and then the interval within the pipe to the seafloor were successfully logged. The tool was lowered back to 110 m below the pipe for the typical short, quality control repeat pass. After completing the run through the open hole, the tool string could not be pulled into the pipe. After several unsuccessful attempts to work the tool into the pipe, the drill string was lifted, which freed the tool. After recovering the tool, it was discovered that the caliper arm was broken and the armored logging line had been damaged. Following a review of the heave conditions (up to 4 m), the hole condition, tool safety, and operational constraints, it was decided to forgo the deployment of the Formation MicroScanner (FMS)-sonic tool string. After recovering the drill string and disassembling the bottom-hole assembly for transit, we departed for Site U1306 (LAB7A) at 1400 h on 22 October.

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