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doi:10.2204/iodp.proc.329.108.2011

Operations

Transit to Site U1370

After a 56.5 h transit from Site U1369, covering 625 nmi and averaging 11.1 kt, the speed was reduced and thrusters were lowered. Dynamic positioning was initiated over Site U1370 at 1602 h on 26 November 2010. The position reference was a combination of GPS signals. No acoustic beacon was deployed, but a beacon remained on standby in the event of a loss of GPS satellite coverage. While automatic input into the dynamic positioning system was not possible because of a system malfunction, it was possible to manually hold the vessel in position to clear the seafloor with the bottom-hole assembly if necessary.

All times in this section are given in local ship time unless otherwise noted. For most of the expedition, local time was Universal Time Coordinated – 10 h.

Site U1370

Six holes were drilled or cored at Site U1370 (Table T1). The first hole was a washdown hole drilled with the center bit in order to establish the sediment depth of 66.7 mbsf and any hard layers (chert) throughout the formation. Hole U1370B had one mudline core taken before coring problems forced abandonment of the hole. Hole U1370C was drilled to 7.8 mbsf, and the attempt to take a piston core failed. The last three holes were cored successfully with the advanced piston corer (APC) system. The advanced piston corer temperature tool (APCT-3) was deployed four times on Holes U1370D and U1370E. Perfluorocarbon tracer (PFT) for contamination testing was pumped from Hole U1370C onward until the last core was on deck. A total of 26 cores were attempted while coring 206.3 m. The total length of core recovered at this site was 214.59 m. The overall recovery for Site U1370 using the APC coring system was 104%.

Hole U1370A

Rig floor operations commenced at 1602 h on 26 November 2010. The trip to the seafloor was uneventful. The top drive was picked up, the drill string was spaced out, and the hole was spudded at 0230 h on 27 November. The washdown hole was drilled to determine depth of basement. Mudline was established as 5085.7 meters below rig floor (mbrf) using an offset depth from Hole U1370B. After drilling down, basement was established at 5150.4 mbrf (64.7 mbsf). Basement depth was verified by drilling two additional meters into the basement. The bit was pulled back above the seafloor, clearing the seafloor at 0620 h and ending Hole U1370A.

Hole U1370B

After clearing the seafloor, the center bit was pulled by wireline, the vessel was offset 20 m west, and the drill string was spaced out to spud Hole U1370B. After making up the first APC core barrel, the core barrel was run to bottom on the wireline and Hole U1370B was spudded at 0745 h on 27 November. Seafloor depth was established at 5085.7 mbrf with a mudline core. APC coring was terminated after the second core attempt. It appeared as if there was something blocking the seal-bore collar that was preventing the core barrel from seating. The center bit was deployed in order to verify a clean seal-bore assembly and to check flow against the slow circulating rates taken at the start of the hole. Subsequent problems determined that it was most likely the shear pins failing during the deployment of the core barrel. The hole was terminated and several remedial measures were implemented. One core was taken with a total recovery of 7.81 m (100.1%). After Core 329-U1370B-1H was recovered, the bit was tripped back to just above the seafloor, ending Hole U1370B at 1000 h on 27 November.

Hole U1370C

Hole U1370C began at 1000 h when the APC assembly cleared the seafloor after completing Hole U1370B. After offsetting the vessel 20 m north, an attempt to spud Hole U1370C was made. After multiple wireline runs and multiple attempts to spud Hole U1370C, the hole was spudded at 1810 h in an attempt to advance the hole and coring began. During the effort to continue coring, several remediation efforts were attempted. The root problem seemed to be shear pin failure during the wireline trip into the hole. Rig instrumentation indicated that the core line received increasingly high tension variation as the core line was run to greater depth. Variations were ~2500 lb of force. An extra shear pin was added to the system in an effort to land the core barrel with the shear pin assembly intact. This still failed. A 90° heading change was made to try to reduce the overall heave of the vessel. Decreasing weather and the heading change successfully reduced the heave by over a meter. In an attempt to dampen the tension variation, the compensator was opened for core barrel deployment. After a drilled advance of 7.8 m, the core barrel was finally deployed without the shear pin failure that had been experienced all day. With three shear pins installed and the core barrel landed, the mud pump pressure was insufficient to shear the pins and shoot the APC core barrel. Consequently, the core barrel was pulled to the surface and redressed with new shear system components and two shear pins. Hole U1370C was abandoned and the bit cleared the seafloor at 2000 h on 27 November, ending Hole U1370C.

Hole U1370D

Hole U1370D began at 2000 h, when the APC assembly cleared the seafloor after completing Hole U1370C. After offsetting the vessel 20 m east, Hole U1370D was spudded at 2115 h on 27 November. Seafloor depth was established with a mudline core at 5084.7 mbrf. An APCT-3 measurement was taken on Core 329-U1370D-4H. The APC coring system was used to take eight cores to 68.2 mbsf with 70.26 m recovery (103%). After Core 8H, the bit was advanced and rotated into basement to verify basement depth (68.2 mbsf) and the bit was tripped back to just above the seafloor, ending Hole U1370D at 1250 h on 28 November.

Hole U1370E

Hole U1370E began at 1250 h when the APC assembly cleared the seafloor after completing Hole U1370D. After offsetting the vessel 20 m east, Hole U1370E was spudded at 1445 h on 28 November. Seafloor depth was established with a mudline core at 5085.3 mbrf. An APCT-3 measurement was taken on Cores 329-U1370E-3H, 5H, and 6H. The APC system was used to take nine cores to 65.6 mbsf with a 70.2 m recovery (107%). PFT was mixed with the drilling fluid (seawater) and pumped on all cores for contamination testing. After Core 9H, the bit was advanced and rotated into basement to verify basement depth (65.6 mbsf) and the bit was tripped back to just above the seafloor, ending Hole U1370E at 0855 h on 29 November.

Hole U1370F

Hole U1370F began at 0855 h when the APC assembly cleared the seafloor after completing Hole U1370E. The vessel was offset 20 m south of Hole U1370E. After making up the first APC core barrel, the core barrel was run to bottom on the wireline and Hole U1370F was spudded at 1010 h. Seafloor depth was established with a mudline core at 5084.8 mbrf. The APC system was used to take eight cores to 64.7 mbsf with a 66.32 m recovery (102.5%). PFT was mixed with the drilling fluid (seawater) and pumped on all cores for contamination testing. After Core 329-U1370F-8H, the bit was advanced and rotated into basement to verify basement depth (64.7 mbsf). The drill string was tripped to the surface, clearing the rotary table at 0530 h on 30 November. The rig floor was secured for the 499 nmi transit to the next site, ending Hole U1370F and Site U1370 at 0600 h.

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