SUMMARY OF LEG 182 ENGINEERING AND DRILLING OPERATIONS
Port Call Activities and Transit to Site 1126 (GAB-04B)
Leg 182 officially began at 1000 hr on 8 October 1998 with the first line ashore in Wellington, New Zealand, ending Leg 181. All subsequent times in this volume are local time (e.g., Universal Time Coordinated [UTC] + 8 hr for the Leg 182 operational area), unless otherwise noted. Leg 181 had been extended 12 hr, shortening the time available to complete port call activities for Leg 182, despite the vessels eventual early arrival. After completion of most of the port call activities, the ships departure was scheduled for 0800 hr on 13 October. However, we were delayed further by a storm with sustained winds of 45 kt, gusting to 60 kt.
The storm moderated overnight to 25-kt winds with 35-kt gusts and the ship departed at 0809 hr on 14 October. We quickly encountered the first of numerous gale-force storms, and the ships course was diverted several times to the north to avoid the strength of the storms and to maintain speed. Much of the transit across the Tasman Sea encountered nearly continuous high seas and swells (as high as 9 m) with green water and spray over the bow, and an opposing current (~1 kt) and winds (2550 kt). The weather did not moderate for more than a few hours at a time until the ship passed through Bass Strait into the Great Australian Bight. Propulsion motor P 17B failed with armature problems on the transit and was inoperable for the rest of the leg. The 2375-nmi sea voyage required 11.8 days (8.4 kt average) instead of the 8.7 days (at 10.5 kt) that was projected precruise. The longer transit time, combined with the extra day spent in Wellington waiting on the weather, forced the decision to shift the initial site from GAB-03B to GAB-04B. GAB-03B was dropped to alternate status.
A positioning beacon was launched at 2257 hr on 25 October to start Site 1126. The ship was stabilized on position, and an advanced hydraulic piston core/extended core barrel (APC/XCB) bottom-hole assembly (BHA) was run to 796 meters below rig floor (mbrf) and Hole 1126A was spudded at 0530 hr on 26 October. Core 1H recovered 9.69 m, which was not appropriate for establishing a good mudline. The bit was repositioned to take another mudline core, ending Hole 1126A at 0600 hr on 26 October.
The ship was not moved, and Hole 1126B was spudded at 0630 hr on 26 October. The bit was positioned at 792 mbrf, and Core 1H recovered 6.56 m, indicating the seafloor was at 783.8 meters below sea level (mbsl). APC coring advanced to 104.0 meters below seafloor (mbsf), orienting Cores 3H to 11H. Cores 10H to 12H encountered chert horizons, causing only partial strokes of the piston. The APC shoe was damaged during firing of Core 12H, bending the cutting shoe and plugging the nozzles in the core bit. The next APC coring attempt failed despite firing pressures of 3000 psi with the bit at 1 m off bottom; therefore, an XCB bit was dropped to deplug the throat of the drilling bit. This configuration allows water to circulate through the XCB core barrel during drilling and wash away any soft material. Thus, Core 13W (104.0109.5 mbsf) was considered a wash interval; however, a few pieces of chert were recovered (0.2 m) and curated.
APC coring resumed from 109.5 to 124.5 mbsf with Core 15H encountering chert layers and bending another APC shoe. The XCB bit was dropped again and the chert interval (124.5128.8 mbsf) was washed with no recovery. APC coring advanced to 160.3 mbsf (Core 20H) before penetration was again prevented by chert horizons. The Davis-Villinger Temperature Probe (DVTP) was deployed after Core 19H, but the ships heave prevented quality data collection. Coring continued with the XCB to 263.3 mbsf (Core 32X) and was terminated when the last four coring runs destroyed both hard and soft XCB cutting shoes. The bit was pulled and cleared the seafloor at 1415 hr on 27 October.
The ship was moved 20 m east of Hole 1126B, and Hole 1126C was spudded at 1540 hr on 27 October. The bit was positioned at 794 mbrf, and Core 1H recovered 8.48 m, indicating a water depth of 783.8 m. APC coring advanced to the approximate depth of the chert horizons found in Hole 1126A. Cores 3H through 9H were oriented and Adara tool heat-flow measurements were made during Cores 4H, 6H, and 8H. As with the DVTP, the heave from long-period swell disturbed all three Adara tool runs. Coring continued with the XCB from 84.5 to 138.4 mbsf through the chert-rich intervals. We switched back to APC coring for Core 16H; however, the core was a partial stroke (6.0 m) and the APC shoe had been dented severely. A final XCB core (17X) was cut from 144.4 to154.0 mbsf with 46% recovery. The bit was pulled and cleared the rotary at 0615 hr on 28 October, ending Hole 1126C.
A rotary core barrel (RCB) BHA was run to the seafloor, which was tagged at 795.0 mbrf (783.8 mbsl). The hole was drilled from 0 to 150.0 mbsf at 42.9 m/hr with a center bit in place. The interval from 150.0 to 463.3 mbsf was RCB cored (Cores 1R33R) with 12.9% recovery. Recovery was poorest in soft nannofossil oozes interbedded with chert because of chert blocking the throat of the bit or jamming in the core catcher, preventing softer material from entering the core barrel. The recovery increased to ~22% below 350 mbsf as the induration increased.
After coring was terminated, the hole was prepared for logging. This preparation included a wiper trip to 107 mbsf, circulation of a sepiolite mud pill, and release of the bit. The drill pipe was pulled to 117 mbsf, which placed the end of pipe below the first prominent chert layer to protect the logging tools and wireline in anticipated high-heave conditions. The triple combination log was run from 441 mbsf (22 m off bottom) to the end of pipe at 117 mbsf. During logging, the wireline heave compensator occasionally reached its maximum stroke of 6 m. The caliper on the triple combo logging tool showed that hole conditions were poor with prominent washouts. To protect the tool from damage, the formation microscanner (FMS) was not deployed in these conditions. Therefore, the sonic tool was combined with the Geologic High Resolution Magnetic Tool (GHMT; magnetic susceptibility only; total field was inoperable), and the tool string was run from 440 mbsf to the mudline. In the final logging run, the generator-injector (GI) air gun and the well seismic logging tool (WST) were deployed for a check-shot survey. The drill pipe cleared the rig floor at 1530 on 30 October, ending operations at Site 1126.
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