162 Preliminary Report

Site 982

The operational plan for Site 982 (NAMD-1) called for three APC holes to approximately 200 mbsf, and one XCB hole to 500 mbsf. Standard Quad-combo and FMS logging were to be conducted in the deep hole, with the added possibility of running the magnetic susceptibility tool.

At 1506 hr on 15 July the ship slowed down to 6.0 kt and the seismic gear was deployed for a 9 nmi (about 1.5 hr) predrilling survey of Site 982 (NAMD-1). Based on the survey we chose Site 982 to be about 300 m to the northeast of the proposed NAMD-1 site in order to avoid small-scale faulting observed in the seismic records. By 1815 hr on 15 July, the seismic profiling gear had been recovered, the vessel had returned to the drilling location based on GPS coordinates, and the positioning beacon had been deployed initiating Site 982 and Hole 982A.

A standard APC/XCB BHA was used for all holes at Site 982, including a nonmagnetic drill collar. Subsequent holes (982B and C) were offset 15 m to the north, while Hole 982D was offset 5 m to the north. The mudline was established for each hole except Hole 982D. The APC firing depth was offset by a few meters for subsequent holes in order to establish continuous sediment sections, except for Hole 982D.

Coring at Hole 982A proceeded without incident until Core 982A-27H would not come free with 100,000 lb of overpull. The previous Core 982A-26H required 40,000 lb of overpull. Both cores had full stroke indications. The washover technique was used, but was limited to 4.0 m due to drilling kelly limitations. After several heave cycles and limited jarring attempts, the driller continued to apply increasing tension to the coring assembly. During an upheave the overpull reached 150,000 lb and the barrel apparently came free. Upon recovery it was found that the pin thread on the upper inner core barrel had parted, leaving the lower 15-ft inner barrel, liner seal sub, and core shoe in the hole. Advance by recovery was used to determine the final hole depth, and the hole was terminated at that point. Hole 982A reached the scientific target for triple coring, and Hole 982B was deepened instead of this hole.

Coring at Hole 982B was without incident until Core 982B-26H. This core penetrated to a depth of 243.0 mbsf, just one core above the point where the high overpull and subsequent inner barrel connection failure occurred. Although Core 26H only required 25,000 lb of overpull to extract it from the formation, it was considered prudent to switch to XCB coring at that point. Coring was suspended at a depth of 614.9 mbsf when the scientific target was reached. The last four XCB cores, from 576.4 to 614.9 mbsf, were characterized by low recovery that averaged between 2% to 8%.

Upon completion of coring operations at Hole 982B, two annular-hole volumes of seawater were circulated. A wiper trip identified no overpull or drag. Only 1.5 m of fill was found at total depth (TD), which was readily circulated out. The pipe was pulled to a logging depth of 82.6 mbsf. No drilling mud was required during the drilling operation, and the hole was considered to be in excellent condition. Two successful logging runs were made. The first run, using the Quad combo suite of tools, was deployed to within 1.9 m of bottom. The second run, using the FMS, reached to within 4.9 m of bottom. After completing the logging operations, the upgraded LDEO/BRG wireline heave compensator control system was tested. After the final suite of tools was recovered and the logging sheaves were rigged down, the drill pipe was tripped above mudline, clearing the seafloor and ending Hole 982B.

Coring at Hole 982C proceeded without incident until the scientific target for the hole had been reached. Core orientation on this hole using the Tensor tool was conducted on Cores 982C-3H through 7H.

The vessel was offset 5 m north in preparation for spudding Hole 982D. This hole was to be a single APC core across an area not recovered completely in the previous three holes. The same water depth as Hole 982C was used as a reference point for drilling to 20 mbsf. APC Core 1H was then taken, recovering 9.76 m. The positioning beacon was recovered and the vessel was secured for transit. We were underway at 2112 hr on 19 July 1995.

To Operations Site 983

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