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doi:10.2204/iodp.proc.317.103.2011

Operations

Transit to Site U1351

After a 1 day transit from Wellington, New Zealand, covering 257 nmi at an average speed of 11.4 kt, the R/V JOIDES Resolution was positioned over Site U1351 on 18 November 2009 at 0931 h (all times are ship local time, Universal Time Coordinated [UTC] + 13 h). The position reference was a combination of Global Positioning System (GPS) and an acoustic beacon on the seafloor, weighted heavily toward the acoustic beacon (80%). The positioning beacon (FSI BAP-547W, SN 1025, 14.0 kHz, 200 dB) was deployed at 1030 h.

Site U1351 overview

Three holes were drilled at this site (Table T1). The first two holes were cored with the advanced piston corer (APC)/extended core barrel (XCB) coring systems. Total core recovery was 332 m. Average recovery rates for Site U1351 were 87% with the APC coring system, 23% with the XCB coring system, and 31% for all cores. Hole U1351B was logged with limited success. The third hole was drilled with a 9⅞ inch tricone bit for logging purposes. Logging was attempted, but the tool became stuck and had to be recovered. The third-generation advanced piston corer temperature tool (APCT-3) was deployed three times, and the Sediment Temperature (SET) tool was deployed twice. Data from four out of five deployments were severely compromised, probably because of sediment that had fallen to the bottom of the hole and/or motion at the bit.

Hole U1351A

Rig floor operations commenced at 0931 h on 18 November. The drill string was spaced out, placing the bit at 126.5 m drilling depth below rig floor (DRF) or 4.9 m above the "corrected" precision depth recorder (PDR) depth of 131.4 m DRF. The first APC barrel recovered ~2.7 m of core, and an official seafloor depth was established at 133.3 m DRF. APC coring continued through Core 317-U1351A-6H to 28 m DSF using standard steel coring assemblies. All cores after Core 317-U1351A-2H were partial stroke cores, indicating very firm near-surface sediments. The hole was terminated after Core 317-U1351A-6H.

Contamination testing was done on all cores with perfluoromethylcyclohexane (PFT) and microspheres. A temperature measurement was taken with the APCT-3 at Core 317-U1351A-4H. Average recovery for Hole U1351A using the APC coring system was 98%. The drill string was pulled back to the seafloor, and the bit cleared the seabed at 2330 h on 18 November.

Hole U1351B

Hole U1351B officially began at 2330 h on 18 November. The vessel was offset 20 m south of Hole U1351A, and coring in Hole U1351B began at 0045 h on 19 November. Hole U1351B was piston cored to 94.7 m, with a total recovery of 81.12 m (81% recovery). Orientation was measured on the first five cores, and then poor APC coring conditions forced the tool to be removed. The XCB system was deployed for most of the remaining interval (Cores 317-U1351B-14X through 116X [94.7–1030.6 m DSF]). Recovery was acceptable (ranging from 20% to 100%) from the top of the XCB interval to ~429 m DSF, where it dropped to nearly zero for seven cores. The decision was made to switch back to the APC system three times (Cores 317-U1351B-57H through 59H, 65H, and 78H) in an attempt to improve recovery. However, penetration was short each time (0.8–4 m; recovery was nominally high but was based on recovered length), and XCB coring was resumed. The average core recovery for all XCB cores was 23%. Coring was terminated at 1030.6 m DSF after the XCB core barrel became stuck inside the bottom-hole assembly (BHA).

After the core barrel was freed, a decision was made to stop coring and log Hole U1351B. A 50 bbl high-viscosity mud sweep was pumped to clean the hole, and the hole was displaced with 420 bbl of 9.0 ppg mud with a 100+ Marsh funnel viscosity. The drill string was tripped back to 80 m DSF, and the triple combination (triple combo) tool string was rigged up and run to the bottom. Hole conditions before logging were good, but the gauge of the hole was largely unknown. The first logging run revealed that the hole was oversized over most of its length. Next, the Formation MicroScanner (FMS)-sonic tool string was rigged up and deployed. The tool failed to pass 618 m wireline log depth below rig floor (WRF), indicating that the hole had collapsed and bridged near that depth. The hole was logged from that point upward. A 12 bbl cement plug was pumped according to IODP policies for drilling on a continental shelf, with the string at 283 m DSF. The drill string was tripped back to the surface, and the bit cleared the rotary table at 1800 h on 25 November, ending Hole U1351B.

Contamination testing for microbiology was done at regular intervals (every ~50 m) throughout Hole U1351B. Both PFTs and microspheres were deployed. Temperature measurements were taken with the APCT-3 at Cores 317-U1351B-10H and 12H and with the SET tool at Cores 317-U1351B-16X and 42X, with mostly poor results.

Average core recovery in Hole U1351B was 84% for the APC system and 23% for the XCB system. Total recovery for Hole U1351B was 304.5 m out of a cored interval of 1030.6 m (30% recovery rate).

Hole U1351C

The objective of drilling Hole U1351C was to provide a dedicated, fresh hole for wireline logging without coring, and operations officially began at 1800 h on 25 November. The ship was offset 30 m south of Hole U1351B. A new BHA was made up with a 9⅞ inch tricone bit fitted with a mechanical bit release. After tripping the BHA to the seafloor and picking up the top drive, drilling in Hole U1351C began at 2335 h on 25 November. The hole was drilled to 1100 m DRF and swept clean with a 50 bbl high-viscosity mud sweep.

At 1915 h on 27 November, while the hole was being swept clean with mud in preparation for logging, a sudden wind change forced the vessel outside its maximum positioning offset (8% of water depth, or ~10 m). The vessel lost power to three of its six forward thrusters while trying to respond to the sudden wind shift. Position and power were reestablished within 15 min. The maximum excursion from the hole was 38 m. With all drilling parameters still normal, Hole U1351C was displaced with logging mud in preparation for logging. The drill string was tripped to 80 m DSF, and the section of drill pipe that was located at the seabed during the excursion was inspected after it was recovered at the surface. No damage to the drill string was visible.

The triple combo logging string was assembled and run into Hole U1351C. When the tool was at ~912 m wireline log depth below seafloor (WSF), the winch lost weight, indicating that the tool was stuck. The tool could not be moved either up or down, so the logging line was cut, and the drill pipe was tripped in over the logging line in an attempt to recover the triple combo logging string. The logging tools were eventually recovered after tripping over the wireline from 80 to 708 m DRF. The tools were pulled up into the drill string, and the logging line was pulled up onto the rig floor using T-bars until sufficient length was recovered to attach the line to the coring winch. After the line was spooled onto the coring winch, the coring winch was used to recover the logging tools. The logging tools were set back on the rig floor, the drill string was pulled back to ~285 m DRF, and the hole was cemented with 10 bbl of 14 ppg cement. The drill string was then tripped back to the rig floor and secured for the 8 nmi transit to the next site, ending Hole U1351C at 0200 h on 30 November.

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