164 Preliminary Report

SITE 994
(Proposed Site BRH-4)

Hole 994A The operational plan at Site 994 called for two short holes from which sediments would be sampled for microbiological studies, followed by an APC/XCB hole to 750 mbsf. The APC/XCB bit and bottom-hole assembly (BHA) used at Sites 991, 992, and 993 were used in this hole as well. The first APC core attempt had full recovery and no mudline. The pipe was moved up 5 m, and Hole 994A was spudded at 2108 hr on 7 November. The seafloor was 2797.6 mbsl, based on recovery. APC Cores 164-994A-1H to 4H were taken from 0 to 36.4 mbsf. During this time a Force 9 storm hit with rain and continuous lightning, 55-kt winds, and 15-ft seas. The ship was forced 55 m off location, resulting in a yellow 2% (of water depth) warning light; coring operations, however, continued unabated. After the coring objective was reached, the hole was terminated, and the pipe cleared the seafloor at 2350 hr on 7 November.

Hole 994B Hole 994B was drilled to obtain a single mudline core. Hole 994B was spudded at 0030 hr on 8 November, without moving the ship from the position of Hole 994A. The seafloor was 2797.6 mbsl based on recovery. APC Core 164-994B-1H was taken from 0 to 6.9 mbsf, and the hole was then terminated.

Hole 994C The ship was moved 10 m south, and Hole 994C was spudded at 0115 hr on 8 November. The seafloor was 2799.1 mbsl based on recovery. Seventeen APC Cores 164-994C-1H to 19H were taken from 0 to 158.4 mbsf, with PCS cores taken at 9P and 18P. Cores were oriented using the tensor tool starting with Core 3H and including all other APC cores. The Adara temperature tool was run with 10 min burial at Cores 4H, 6H, 10H, 13H, 16H, and 20H. When liners were removed from the core barrel, some gas pockets were noted in the cores and occasional splits in the liners occurred, but no special precautions were taken because of low total gas volumes and pressures.

The FWS was run at 51.0 mbsf and again at 100.4 mbsf. For both runs, the sampler was buried with 10k lb set-down weight for a 10-min sample period. When retrieved after each run, the 2 micron screen filter on the sampler was clogged with clay. Water recovered from both runs was determined by analysis to be a mixture of borehole water and water that is loaded into the tool for operational reasons before the run.

Fifty-seven XCB Cores 164-944C-20X to 84X were taken from 158.4 to 703.5 mbsf, with 537.1 m cored and 332.63 m recovered (61.9% recovery). Cores 164-944C-28X and 29X had very low recovery, and mud was found on the check valve, indicating that it had been blown out of the top of the liner. Core 164-944C-30X had enough gas pressure in the inner core barrel to blow out the core and liner, which then fell down the V-door slide.

Ten PCS cores were taken at Hole 994C, with a total of 10.0 m cored and 1.28 m recovered (12.8% recovery). The PCS retained greater than 75% of hydrostatic pressure upon retrieval in nine of these runs and greater than 98% of hydrostatic pressure in six runs. It also recovered more than 15 cm of sediment in seven of these runs. The new PCS push-in-type shoes were run twice (Cores 36P and 45P), and the new PCS rotary auger-type bit was run eight times. Coring parameters were varied in an effort to maximize recovery. The pressure in the PCS chamber was checked as soon as possible, and the chamber was placed in an ice barrel. Pressured gas and water samples were recovered first through a choke manifold in the engineering van, and the core was recovered last (usually several hours later). At this time, the core was examined for lithologic details and a section was squeezed for interstitial water. The sampling manifold was simplified several times to facilitate depressurization of the core and to reduce sampling losses.

Hole 994D The ship was moved 20 m north-northeast, and Hole 994D was spudded at 0300 hr on 15 November in order to provide a more in-gage hole for VSP clamping and logging. The seafloor was 2799.1 mbsl, based on Hole 994C. An 11-7/16 in. hole was drilled from 0 to 100.0 mbsf. One APC core (Core 164-994D-1H) was taken from 100.0 to 109.6 mbsf. The hole was drilled with a center bit from 109.6 to 241.8 mbsf. Four XCB cores (Cores 164-994D-2X to 5X) were taken from 241.8 to 280.3 mbsf. The hole was then drilled with a center bit from 280.3 to 376.7 mbsf. Four XCB cores (Cores 164-994D-6X to 9X) were taken from 376.7 to 415.0 mbsf, after which the hole was drilled with a center bit to 670.0 mbsf. A 35-bbl sepiolite mud sweep was circulated and a wiper trip was made to 70 mbsf to condition the hole for logging. The hole was reamed from 508 to 670 mbsf with 22 m of fill on bottom (clay pushed to bottom without circulation or rotation). The sediments from 240 to 300 mbsf and below 450 mbsf were elastic, and reaming was ineffective because the hole closed in quickly after the bit was withdrawn. The hole was displaced with sepiolite/seawater mud. At 0515 hr on 16 November, the Cape Hatteras arrived on location from Beaufort, N.C., in order to conduct a two-ship walkaway vertical seismic profile experiment.

The initial attempt to run the VSP log with the pipe at 494.5 mbsf was unsuccessful because of tight hole conditions. The drill pipe was pulled to 75 mbsf, and the conical side-entry sub (CSES) was inserted so that the drill pipe could be used to punch through constrictions that logging tools could not go through. The CSES was picked up in 4.75 hr ,and drill pipe was run to 661 mbsf with as much as 35k lbs drag. The VSP tool was deployed and pushed through the XCB bit by pumping; however, the logging cable was damaged, and the tool had to be pulled together with the CSES and drill pipe. The cable was reheaded, and the VSP tool was deployed again using the CSES and drill pipe. This time, the Gearhart fitting on the pendant rotated, damaging the conductors in the Gearhart head. After retrieval, the Gearhart head was repaired. Just before the fourth deployment, the VSP tool was found to have an electrical leakage. The backup WHOI tool was deployed in its place and rerun through the CSES and drill pipe to 650 mbsf, after which the first walkaway VSP began with the Cape Hatteras. The VSP tool stuck at 635 mbsf on its second clamping and was worked free; however, the clamping arm drive train was damaged. The VSP tool was retrieved through the CSES.

While the two VSP tools were repaired, the Quad-combination logging tool (without the compensated neutron log [CNL]) was run to 628 mbsf using the CSES. The first VSP tool was rerun with the CSES to 650 mbsf, after which the Cape Hatteras conducted a walkaway VSP. The VSP clamping arm failed after three clampings, and the Cape Hatteras was released at 1110 hr on 19 November. The zero-offset VSP was continued to 113 mbsf by suspending the tool in the hole at 20-m intervals and confirming arrivals on the geophone using the scope in the Underway Geophysics Lab. After the zero-offset VSP was completed, the bit was washed in the last 30 m. The shear wave tool was then run to 615 mbsf, and logs were taken successfully. The CSES was pulled back to the moonpool, and the logging tool was retrieved. Hole 994D was then terminated, and the bit cleared the seafloor at 0340 hr on 20 November. The bit was pulled 100 m above the seafloor for the move in DP mode to Site 995.

To Operations Site 995

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