164 Preliminary Report

SITE 996
(Proposed Site BRD-1)

Hole 996A Hole 996A was spudded at 0545 hr on 4 December. The first APC core shot was observed with the TV, and the seafloor was at 2169.6 m water depth. APC Cores 164-996A-1H to 2H were taken from 0 to 9.5 mbsf. Core 2H was a partial stroke that hit a hard carbonate. The VIT frame was pulled to permit rotation with the XCB coring system. Cores 3X to 6X were taken from 9.5 to 47.5 mbsf. Coring parameters indicated a soft matrix with a hard crust from 10 to 15 mbsf and 28 to 30 mbsf. The last three XCB cores had no recovery. PCS Core 7P was taken from 47.5 to 48.5 mbsf and recovered 3326 psi. APC Cores 8H to 9H were taken from 48.5 to 63.0 mbsf. Verbal approval was obtained from ODP to core from 50 to 63 mbsf to collect more hydrate. H2S was noted in APC Cores 1H to 2H with concentrations of 60 to more than 100 ppm (maximum detector range). Gas masks were used, and entry to the catwalk area was restricted. A fan was used to blow gas out of the area. Cores were sectioned and laid on the grating to degas, and holes were drilled in the liners. Most cores degassed within 30 min, but some cores required more than 2 hr to reach less than 10 ppm H2S. Some core liners were cut in the lab and carried outside to be split and opened for degassing. As a result of the H2S gas, hydrate could not be readily sampled in the upper cores.

Hole 996B The ship did not move, and Hole 996B was spudded at 1735 hr on 4 December in an effort to obtain near-surface sediments for shore-based microbiological studies. The bit was positioned at 2166.6 mbsl (3 m higher than on Hole 996A) for Core 164-996B-1H, but the core blew apart in the liner, and the sediment blew out on the deck. Recovery was 3.4 m.

Hole 996C The ship did not move, and Hole 996C was spudded at 1855 hr on 4 December in an effort to obtain more near-surface sediments. The bit was positioned at 2163.6 m (6 m higher than on Hole 996A), but Core 164-996B-1H was an incomplete stroke. The core barrel could not be retrieved after 2.5 hr, so the drill string was pulled. The core barrel was bent by the impact with a hard layer (probably carbonates) within 2.6 m of the surface.

Hole 996D While running in the hole with the same BHA, the ship was moved 40 m west. Hole 996D was spudded at 0725 hr on 5 December. The seafloor was estimated at 2173.1 mbsl, based on an apparent seafloor penetration of 3.5 m into a hard crust. Core had apparently fallen out of the core barrel (i.e., actual recovery on Core 164-996D-1H from 0 to 3.5 mbsf was only 0.40 m). The core barrel was bent and had a broken shoe section. The XCB coring system was picked up, and XCB Cores 2X to 3X were taken from 3.5 to 22.6 mbsf, with 1% recovery. Coring parameters indicated a soft matrix with a moderately hard crust from 13 to 14 mbsf and 17 to 19 mbsf. Core 4H from 22.6 to 32.1 mbsf had 92% recovery, but the overpull was 60k lb, with a hard carbonate layer at 29 to 32 mbsf. Core 5X was taken from 32.1 to 41.7 mbsf, with 3% recovery. APC Core 6H was taken from 41.7 to 51.2 mbsf, and PCS Core 7P was taken from 51.2 to 52.2 mbsf. It was recovered at 2974 psi (91% of hydrostatic pressure at the recovery depth) but contained no sediment.

Hole 996E The ship was moved 80 m east of Hole 996D, and Hole 996E was spudded at 0725 hr on 5 December. The seafloor was estimated at 2170.0 mbsl, based on recovery. APC Cores 164 996E-1H to 2H were taken from 0 to 13.6 mbsf in a soft matrix and bottomed out in a hard crust. XCB Core 3X was taken from 13.6 to 23.2 mbsf in the hard crust. APC Cores 4H and 5H were taken from 23.2 to 42.2 mbsf in a soft matrix. XCB Core 6X was taken from 42.2 to 51.8 mbsf in a hard crust. A final APC Core (7H) was taken from 51.8 to 61.3 mbsf in a soft matrix, and PCS Core 8P was taken from 61.3 to 62.3 mbsf. It was recovered at 944 psi (29% hydrostatic) but contained no core. The PCS actuator was found to be sanded up. The drill string was pulled and inspected on the way out. The beacon-recall sender unit in the hull was found to be defective, and both beacons were recalled with the portable unit and recovered. This could explain the two beacon-recall failures earlier in the leg


The sea voyage to Site 997 covered 98 km in 4.2 hr at 12.6 kt average. A Datasonics 354M beacon was dropped at the GPS coordinates. Drillers were advised of the increased potential for hydrocarbons at Site 997A, based on geological and seismic evidence, dynamic well-control procedures were reviewed, and 10.5-ppg kill-weight mud was prepared.

To Operations Site 997

164 Table of Contents

Publications Home

ODP Home