Previous   |    Next

doi:10.2204/iodp.proc.303306.111.2006

Operations

Expedition 306 officially began with the first line ashore on Ponta Delgada, Azores (Portugal), at 1805 h on 2 March 2005. The third Ponta Delgada port call in a row for the JOIDES Resolution, which included refueling and restocking bentonite and attapulgite bulk drilling mud, was concluded at 0806 h on 9 March, ~1.8 days behind schedule because of problems with the passive heave compensator (PHC) seal replacement and severe weather that significantly hampered (and slowed) the PHC repair work. Jeff Fox, Director, Science Services, Integrated Ocean Drilling Program (IODP)-Texas A&M University (TAMU), attended the port call accompanied by the new TAMU Dean of Geosciences, Dr. Bjorn Kjerfve.

Hole U1312A

We completed the 344 nmi transit from Ponta Delgada to Site U1312, averaging 10.3 kt, at 1730 h on 10 March 2005 and spudded Hole U1312A at 0830 h on 11 March. Core 1H was fully recovered (10.08 m), suggesting a seafloor depth of 3533.0 mbrf (Table T1). Because of excessive heave (>5 m), initial coring conditions were not optimal and a more realistic seafloor depth estimate was obtained later in Hole U1312B. APC coring utilizing nonmagnetic core barrels continued to a depth of 237.5 mbsf. The first several cores (1H through 10H; to 95.0 mbsf) had questionable shear pressures, and Core 1H required two wireline runs to recover because of a sheared overshot pin. The swell height decreased after Core 10H, and coring system performance improved accordingly. Coring in Hole U1312A was terminated after recovering Core 25H. Drillover was required for recovery of Cores 23H through 25H, and all core barrels fully stroked. Drillover for the last core required 2 h in the semi-indurated white ooze, and Core 23H was recovered bent. Coring may have continued further; however, risk to the equipment was significant, time required for further advancement was reaching a diminishing return, and the Co-Chief Scientists were concerned about initiating Hole U1312B while heave conditions remained low (~1.5 m). In Hole U1312A, we cored 237.5 m, recovering 248.07 m (recovery = 104.45%) (Table T1).

Hole U1312B

After the seafloor was cleared, the vessel was offset 25 m to the northwest of Hole U1312A. Hole U1312B was spudded at 2115 h on 12 March 2005, with the bit positioned at a depth of 3528.0 mbrf, 5.0 m higher than at Hole U1312A. Core barrel 1H advanced 9.5 m and recovered 3.92 m of sediment, placing the seafloor depth for Hole U1312B at 3533.6 mbrf. After successfully achieving a good mudline core, piston coring advanced to 231.9 mbsf. The core line failed at the rope socket while attempting to recover Core 18H, necessitating a wireline fishing trip for the core barrel and sinker bar assembly. Coring continued through Core 25H (231.9 mbsf) as weather conditions progressively deteriorated, leading to another damaged core line at the rope socket and twisted piston rods. Before repairs were completed, weather conditions deteriorated to a point that precluded additional coring. A wind shift and increased velocity forced a heading change to maintain position over the hole. This caused excessive roll, as the ship was exposed to multiple large swells coming from different directions. Because the electrical supervisor expressed concern about the ability to keep the ship on location, the drill string was pulled out of the hole, clearing the seafloor at 0245 h on 14 March. The ship was allowed to drift off location to minimize vessel motion during the remainder of the pipe trip. By 1700 h on 14 March, the ship was secured and began the slow dynamic positioning move into the prevailing seas back over the drill site. At 0430 h on 15 March, positioning beacon SN 2199 (15 kHz, 211 dB) was recovered, officially ending operations for Hole U1312B and Site U1312. In Hole U1312B, we cored 231.9 m, recovering 236.84 m (recovery = 102.08%) (Table T1).

Top of page   |    Previous   |    Next