Operations for the continental shelf transect (Sites 1100, 1102, and 1103) were interrupted by a brief detour to the nearby continental rise (Site 1101), which was cored while waiting for the environmental conditions to improve on the shelf. The chronological order of events included drilling Holes 1100A through 1100D, proceeding to and completing operations at Site 1101, returning to Hole 1100D, and finally conducting operations at Sites 1102 and 1103.
The 77-nmi distance between Site 1099 in the Palmer Deep and Site 1100 on the outer continental shelf was traversed in 9.6 hr. The average speed, 8.8 kt, was slower than normal because of a combination of 7-m swells and 3-m seas, both nearly at right angles to the ship's track.
The beacon was dropped at Site 1100 at 1445 hr on 14 March, and an RCB BHA with a new C-4 coring bit was deployed. Because of the restriction of 2 m maximum heave in 300-650 m water depth, the vessel stood by from 1730 to 2000 hr to allow a large swell to ease.
Hole 1100A was spudded at 2030 hr, and coring proceeded to 33.8 mbsf with no recovery before operations had to be stopped because of vessel heave. From 0115 to 0745 hr on 15 March, the vessel stood by while a large mixed swell from the west and north-northwest generated heave exceeding 3 m.
At 0930 hr on 15 March, Hole 1100B was spudded with the RCB and drilled ahead with a wash barrel to 34 mbsf. Once the wash barrel was retrieved, rotary coring began. It advanced only 2 m, however, before operations had to be stopped again because of heave. The BHA was tripped to the drill floor, and the throat of the bit was found to contain cobbles and gravel. The bit was cleaned and the BHA reassembled with the core barrel in place.
After the heave had subsided to acceptable levels, Hole 1100C was spudded. Coring advanced only 5 m, however, before heave again exceeded the threshold. When attempts to retrieve the core barrel with the wireline failed, the drill string was tripped to the surface for the second time. The BHA was partially disassembled in an attempt to discover why the core barrel could not be recovered with the wireline. The core barrel was found to contain more than 4 m of olive gray diamict (81% recovery). Investigation of the BHA revealed that a seal-bore drill collar, which is a standard fixture for the APC/XCB BHA, had been mistakenly added to the RCB BHA. This collar has a narrower inside diameter (3.8 in) than the standard controlled-length drill collar (4.3 in) used with the RCB BHA. The RCB core barrel could not pass through the narrower collar, either down (in Holes 1100A and 1100B) or up (in Hole 1100C), hence the difficulty in recovering core from the first three holes.
Hole 1100D was spudded at 1030 hr on 16 March. RCB coring advanced with poor recovery to 62.5 mbsf and was then stopped while a free-fall funnel (FFF) was deployed. Coring resumed to 76.8 mbsf when operations had to be stopped for a fourth time because of excessive heave. The FFF was re-entered at 0330 hr on 17 March. After washing and reaming to bottom, coring resumed and advanced to 100.9 mbsf. At 1000 hr on 17 March, and for the fifth time on site, coring was interrupted by heave exceeding 2 m. The bit was pulled above the seafloor at 1030 hr.
After deliberating whether to remain on site in difficult heave conditions, the decision was made to move to a new, alternate site in deep water (i.e., beyond the heave restriction) 120 nmi southwest. We hoped that after coring at the new site was concluded, the swell would have abated and would allow another attempt at deepening Hole 1100D. Of the 77.8 hr spent on site, only 20.5 were spent coring; 24.8 were inactive, waiting for the swell to abate, and the remaining time was occupied by reentry, tripping pipe, and so forth, as consequences of the primary disruption. At 2030 hr the drill string was recovered and the beacon commanded into standby. The vessel was under way to Site 1101 at 2030 hr on 17 March.
On completion of operations at Site 1101, we traveled 127 nmi back to Hole 1100D in 11.2 hr at 11.3 kt. The FFF was re-entered at 1700 hr on 20 March. We reached the bottom of the hole and cored from 100.9 to 110.5 mbsf (Core 12R) with 0.54 m of recovery before being forced to stop by the 2-m heave limitation. After waiting about 6 hr, and because hole conditions were not promising, we decided to move to a new site.
After the hydrophones were retracted, the vessel moved 6 nmi to Site 1102 (prospectus site APSHE-01A) using the thrusters. Operations were difficult given the heave, which often exceeded 2 m, and the rocky surface layer, which extended to an unknown depth. We managed to spud four holes, but with little recovery and no real opportunity to deepen them.
At 0645 hr on 21 March a beacon was deployed, and Hole 1102A was spudded at 1015 hr on 21 March. Coring advanced only 7.9 m (Core 1R) when excessive heave forced a halt. At 1425 hr on 21 March, Hole 1102B was spudded; it advanced only 7.5 m, however, when coring was again suspended for excessive heave. While waiting for the swell to flatten, a television survey of the seabed within a 50-m radius of the site was conducted for 2 hr, allowing the choice of a boulder-free alternative hole position. The heave subsided at 0130 hr on 22 March, but only long enough for Hole 1102C to be cored to 6.5 mbsf. Finally, Hole 1102D was spudded at 0945 hr. Unfortunately, hole conditions were poor. After coring to 14 mbsf in 3.25 hr, half the advance was lost when the driller picked up to 7 mbsf to retrieve the core. For the next 1.5 hr, the hole was washed and reamed with high, erratic torque. Three meters was drilled but were again lost when the driller pulled back. It was clear that this site was populated with boulders, rocks, and gravel, to a much greater depth than was visible at the seabed, and was virtually undrillable. Of the 34.8 hr spent at Site 1102, 15.3 were passed waiting on weather related to excessive heave and only 8.5 in actual coring. The remaining time was used for tripping, washing and reaming, and the small television survey.
At 1730 hr, the vessel began the 16-nmi transit to Site 1103 (prospectus site APSHE 10A), arriving at 2000 hr on 22 March. Hole 1103A was spudded at 0130 hr on 22 March, with low expectations stemming from our recent experience with excessive ship heave. This time, however, fortune smiled, and ship heave was not a problem for the remainder of the leg.
RCB coring advanced quickly to 180.3 mbsf with very low recovery (2.6% or 4.7 m), which was attributed to a soft till matrix and hard rocks becoming jammed in the core catcher. At 1900 hr on 23 March, the third FFF of the leg was deployed as insurance in case the weather deteriorated or an iceberg appeared. Coring resumed at 2015 hr and continued with improving recovery and slowing rates of penetration. Coring ended at 363.7 mbsf at 0730 hr on 25 March to allow time for logging. The average recovery for the hole improved to 12.3% with an average rate of penetration of 15 m/hr.
The hole was washed and reamed in preparation for logging. Releasing the bit was made difficult by gravel inside the pipe but, following release, the bottom of the drill pipe was pulled back to logging depth (74 mbsf). On the first logging run, the TC tool string was unable to pass a tight spot at 242 mbsf. The hole was logged up from this depth to the seafloor with no repeat run. It took 2 hr to work the tool back into the drill pipe, and the bow-spring of the porosity tool was missing, presumably left in the hole. The second log (GHMT) was also run from 241 mbsf to the seafloor. The FMS was run successfully (from 241 m to the seafloor) only after repairing an electronic problem.
The hole was filled with mud and the drill string retrieved, which took longer than usual because of the routine end-of-leg inspection of drill-collar connections in the BHA. The positioning beacon was recalled, and the vessel departed the site for Cape Town at 1130 hr on 26 March. At 1800 hr, Polar Duke was released in accordance with the contract.
The 3660-nmi transit to Cape Town took 13.8 days at an average speed of 11.3 kt. Leg 178 ended when the JOIDES Resolution was docked in Cape Town at 0900 hr on 9 April 1998.
To 178 Operations Resume
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