With a following wind and calm seas, we made good time traveling at an average speed of 11.2 kt on the 163 nmi transit from Site 1096 to Site 1097 (scientific prospectus site APSHE 05A). During the transit north, 15 icebergs were spotted on radar, and the vessel was required to alter course to avoid one large iceberg. The Polar Duke, which had left Site 1096 before us to scout ahead, reported that there were six icebergs within 15 nmi of site location. The JOIDES Resolution proceeded directly to the Global Positioning System (GPS) coordinates for site APSHE-05A and dropped a positioning beacon at 0615 hr on 6 March.
Because this site did not have sediments suitable for coring with the APC or XCB, a rotary core barrel (RCB) bottom-hole assembly (BHA) was made up with a new Rock Bit International (RBI) C-3 bit and a mechanical bit release (MBR). Hole 1097A was spudded at 1045 hr on 6 March at an estimated seafloor depth of 551.7 m (563.0 mbrf), 1 m less than the computed PDR reading. For the next 13 hr, coring at Site 1097 proceeded slower than expected, and core recovery was very low (3.7% for the first 10 cores) as we attempted to penetrate glacial till through an abundance of cobbles and boulders.
Meanwhile, six icebergs were being monitored within 6 nmi of the rig. A free-fall funnel was deployed late on 7 March to allow us to re-enter the hole, given the likelihood that an iceberg would eventually force us off site. RCB coring resumed and advanced slowly to 164 mbsf, where the drill string stuck in the unstable hole. After 45 min of working the pipe and flushing the hole with mud, the pipe was freed. RCB coring resumed and advanced to 246 mbsf (Core 29R), with improving recovery (but still poor at less than 10%) and faster rates of penetration. At 1600 hr on 8 March, we suspended coring operations and pulled the bit to the top of the hole as an iceberg approached. Just after midnight the iceberg came within 1 nmi, so the drill string was pulled above the seafloor to allow the vessel to maneuver. Because the bit had accumulated 31 hr of rotating time in difficult conditions, we used the waiting time to change it.
At 0710 hr on 9 March, the hole was re-entered in less than 15 min via the free-fall funnel. From 0900 to 1230 hr, the bit was washed and reamed into the unstable formation to 246 mbsf, where circulation was lost after making a connection. The bit was pulled back to 236 mbsf, and attempts were made to clear the drill string and regain circulation. In a last-ditch effort to clear the bit and avoid another round trip of the drill string, a "swab cup" was run in on the wireline to 300 mbrf and then pulled back to the vessel with the drill string connection partially open at the rig floor. The swab cup essentially drained the water in the top 300 m of drill string (spraying the drill floor), which reduced the hydrostatic pressure at the bit. This differential pressure forced formation fluid back up through the bit nozzles, which cleared the blockage. The mud pumps were immediately turned on and the pipe flushed clean. As a precautionary move, a bit deplugger was deployed to clear any obstruction that might be in the throat of the bit.
Coring advanced from 246 to 294 mbsf but then was halted because of excessive vessel heave caused by complex large swells coming from two directions. After sea conditions improved, RCB coring advanced from 294 to 351 mbsf with better recovery (24%) and faster penetration (up to 15 m/hr). This was followed by another 4.3 hr of standby time as ship heave again exceeded 2 m as well as another 5.5 hr of washing and reaming to return to the bottom of the hole.
RCB coring had advanced to 436.6 mbsf by 0545 hr on 11 March with 13.6% core recovery when operations were again interrupted by the approach of an iceberg. The bit was raised to 400 mbsf while the iceberg remained within range. After the iceberg had passed out of range, the drillers encountered several difficulties attempting to reach the bottom of the hole, including having the pipe stuck. At the bottom of the hole, the drillers could not make a connection to retrieve the wash barrel. Because hole conditions were deteriorating, the coring program was terminated.
After the hole was displaced with 85 bbl of 10.5-gallon mud, the drill string was recovered. The bit cleared the seafloor at 1700 hr, and the BHA was at the rotary table at 1800 hr. The drill collar connections were then inspected for any damage incurred as a result of the rough drilling and unusual environmental conditions. The beacon was recovered, and the drilling equipment was secured for transit to Site 1098 by 2100 hr on 11 March.
To 178 Palmer Deep (Sites 1098 and 1099)
To 178 Table of Contents