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doi:10.2204/iodp.proc.303306.112.2006

Operations

We departed the Azores Islands for Site U1313 (proposed Site IRD3A) at 0645 h on Saturday, 26 March 2005, after spending 8 days in the lee of the islands during severe weather conditions. The 277 nmi transit to Site U1313 began with sea-state conditions still somewhat marginal but expected to continuously improve over time. The transit was completed at an average speed of 8.9 kt, and we arrived at Site U1313 at 1425 h on Easter Sunday, 27 March. See Table T1 for a summary of coring at Site U1313.

Hole U1313A

Hole U1313A was spudded at 0005 h on 28 March 2005, establishing a rig floor–corrected seafloor depth of 3423.3 meters below rig floor (mbrf). Core 1H recovered 5.2 m of sediment, indicating a seafloor depth of 3412.3 meters below sea level. The advanced piston coring (APC) system, utilizing nonmagnetic core barrels, continued through Core 31H. Alloy steel barrels were utilized for Cores 32H and 33H, and drillover of stuck APC barrels was required for these last two cores. Tensor core orientation was used for all cores beginning with Core 3H from a depth of 14.7 mbsf. All core barrels fully stroked except for the last one, Core 33H. The cored interval for this hole was 308.6 m, and 319.64 m of sediment was recovered (recovery = 103.6%). The drill string was pulled clear of the seafloor at 1300 h on 29 March, concluding operations in Hole U1313A.

Hole U1313B

Hole U1313B was offset 25 m due north (000°) from Hole U1313A and was spudded at 1430 h on 29 March 2005. The bit was positioned at a depth of 3421.0 mbrf, or 2.0 m deeper than Hole U1313A, and Core 1H recovered 5.90 m of sediment, establishing a rig floor–corrected seafloor depth of 3424.6 mbrf. APC coring continued through Core 20H to a depth of 186.4 mbsf. At that time, operations personnel were advised that the core breaks between Holes U1313A and U1313B were possibly becoming aligned. As a precaution to ensure adequate overlap between holes, the driller was advised to advance the bit 2.0 m further before shooting Core 21H. Coring then continued until 1930 h on 30 March, through Core 32H, to a total depth of 302.4 mbsf. Tensor core orientation was used for all cores beginning with Core 3H from a depth of 15.4 mbsf. All core barrels fully stroked, and no drillover was required in this hole. Nonmagnetic core barrels were used in the recovery of all 32 cores. The cored interval for this hole was 300.4 m, and 306.54 m of sediment was recovered (recovery = 102.0%).

After completing coring operations, Hole U1313B was prepared for logging. A wiper trip was conducted from total depth to 74.9 mbrf and back to total depth without difficulty. No fill, drag, or overpull was detected. The hole was swept with one final 30 bbl mud sweep, and the lockable float valve (LFV) go-devil was pumped down to lock open the LFV for the wireline logging tools. The hole was displaced with 140 bbl of sepiolite mud, and the drill pipe was retracted to 80.7 mbsf. The triple combination (triple combo) tool string was deployed (including the General Purpose Inclinometer Tool and Multi-Sensor Spectral Gamma Ray Tool [MGT]) to within 2.0 m of the bottom of the hole. We successfully logged 220 m of the open hole and then the interval within the pipe to the seafloor. The scheduled deployment of the Formation MicroScanner (FMS)-sonic tool string was cancelled because the Lamont-Doherty Earth Observatory (LDEO) Logging Staff Scientist felt that the resistivity signal was too weak to make the deployment worthwhile. After recovery of the wireline tools, new software for the Schlumberger wireline heave-compensated logging winch was briefly tested. The software was tested for ~45 min under a variety of conditions, and the results appeared to be “very promising.” The Schlumberger logging sheaves were rigged down, and the drill string was pulled clear of the seafloor at 1310 h on 31 March, ending Hole U1313B.

Hole U1313C

The drillship was offset 25 m due east (90°) of Hole U1313B. The bit was positioned at a depth of 3417.0 mbrf, 2.0 m shallower than for Hole U1313A. Hole U1313C was spudded at 1440 h on 31 March 2005. Core 1H recovered 2.71 m and established a rig floor–corrected seafloor depth of 3423.8 mbrf. APC coring with nonmagnetic core barrels continued through Core 30H, and alloy steel barrels were used for the last two cores (31H and 32H). Tensor core orientation was used for all cores beginning with Core 4H from a depth of 21.7 mbsf. Drillover was required for recovery of Cores 29H through 32H. All core barrels fully stroked except for the last three (Cores 30H through 32H). The bit was advanced 8.73 m prior to shooting Core 32H. The drill string was pulled clear of the seafloor at 2140 h on 1 April, officially ending Hole U1313C. The cored interval for this hole was 293.4 m, and 305.79 m of sediment was recovered (recovery = 104.2%).

Hole U1313D

The drillship was offset 25 m due south (180°) of Hole U1313C. The bit was positioned at a depth of 3423.0 mbrf, or 4.0 m deeper than for Hole U1313A. Hole U1313D was spudded at 2255 h on 1 April 2005. Core 1H was fully recovered (9.80 m); therefore, the seafloor depth of 3423.0 mbrf was considered suspect. A valid seafloor depth was not critical for this hole because good seafloor measurements had already been obtained on the three previous holes and the emphasis was to maximize recovery in Core 1H. APC coring continued without incident in Hole U1313D through Core 16H to a total depth of 152.0 mbsf. Tensor core orientation was used for all cores, beginning with Core 3H from a depth of 19.0 mbsf. All core barrels fully stroked, and no drillover was required. Nonmagnetic core barrels were used for recovery of all 16 cores. The cored interval for this hole was 152.0 m, and 159.27 m of sediment was recovered (recovery = 104.8%).

The drill string was pulled clear of the seafloor at 1310 h on 2 April, and during the pipe trip positioning, beacon SN 2199 was recovered at 1430 h. After we recovered and stored the drill string, the ship was secured for transit, all thrusters and hydrophones were pulled, and at 2030 h, the ship was switched from dynamic positioning to cruise mode and got under way for alternate Site U1314 (proposed Site GAR1B).

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