164 Preliminary Report

SITE 995
(Proposed Site BRH-6)

Hole 995A The ship was moved 3.0 km to the GPS coordinates for Site 995, and a Datasonics 354M beacon was dropped at 0749 hr on 20 November. A near-seafloor water sample was taken with the PCS tool at 2693.7 mbsl (approximately 84.8 m above the seafloor). After several water cores using an incorrect PDR setting, Hole 995A was spudded at 1400 hr on 20 November. The water depth was 2778.5 mbsf, based on recovery. Eighteen APC cores (164-995A-1H to 20H) were taken from 0 to 165.2 mbsf, with 163.5 m cored and 170.3 m recovered (104% recovery). Two PCS cores (164-995A-9P and 18P) were taken in the APC hole, with a total of 2.0 m cored and 1.69 m recovered (84% recovery). Cores were oriented using the tensor tool, starting from Core 3H and including all APC cores. Adara temperature measurements were taken with 10-min burial time at Cores 2H, 4H, 6H, 10H, 13H, 16H, and 20H.

When liners were removed from the core barrel, gas voids were noted in the cores. The release of the gas in the voids caused some cores to self-extrude from both the tops and bottoms of the liner. The core liner split full length on Core 17H (145.2 mbsf), after which gassy core safety precautions were followed. APC coring was terminated when Core 20H was a partial stroke, required 50k lbs overpull, and the liner was crunched in the inner core barrel and had to be pumped out.

XCB Cores 164-995A-21X to 83X were taken from 165.2 to 704.6 mbsf. Very large gas voids were noted often, and core recovery was reduced by extensive extrusion of sediments from the tops of core liners. Mud smeared the length of nearly empty core liners and was present on the tools at the top of the liner. A temperature probe developed by Davis and Villinger (DVTP) was run for the first time after Cores 164-995A-20H and 995A-33X, and it successfully recorded data during both runs that WSTP temperature and water samples were taken after Cores 3H, 10H, 13H, 18P, 27P, 30X, 34X, 38X, 41X, and 46X. Nine PCS cores were taken at Cores 164 995A-9P, 18P, 27P, 36P, 45P, 48P, 52P, 60P, and 70P, with a total of 9.0 m cored and 4.58 m recovered (50.9% recovery). In addition, a borehole water sample was taken with the PCS after Core 51X.

The new PCS push-in-type shoes were run as deep as possible on Hole 995A to establish their practical range of use, which appears to be down to about 380 mbsf (in moderately indurated claystones requiring XCB drilling at 18k lb weight on bit [wob]). The shoes were pushed in with 5 to 18k lb weight to a depth of +0.7 m (depending on the extension sub and formation induration) and then rotated at 10-40 rpm for 2 min to penetrate an additional +0.3 m. The new PCS rotary auger-type bit was run three times in Hole 995A. The optimum parameters appear to be 15k lb wob at 40 rpm with 150 amps torque, circulating 200 gpm at 475 to 550 psi (to clean the larger bit).

After drilling to 704.6 mbsf, Hole 995A was terminated. The hole was displaced with gel mud, and the pipe was pulled. The bit cleared the seafloor at 1308 hr on 26 November.

Hole 995B The ship was moved 20 m north-northeast in DP mode, and Hole 995B was spudded at 1520 on 26 November. The water depth was 2776.9 mbsf based on recovery. A single mudline APC Core (164-995A-1H) was taken from 0 to 8.3 mbsf. The hole was drilled from 8.3 to 16.0 mbsf, and Core 2H was taken from 16.0 to 25.5 mbsf. The hole was drilled from 25.5 to 100.0 mbsf, and Core 3H was taken from 100.0 to 109.5 mbsf. A WSTP temperature measurement and water sample were taken, and the hole was then drilled ahead from 109.5 to 155.0 mbsf. The WSTP was run a second time, after which the hole was drilled from 155.0 to 200.0 mbsf. A third WSTP run was made, and the hole was then drilled ahead with a wash barrel to 235.0 mbsf.

XCB Cores 5X to 6X were taken from 235.0 to 254.2 mbsf (16% recovery) in an unsuccessful attempt to recover hydrate (gas hydrate was recovered from approximately this depth at Site 994). The hole was drilled ahead with a center bit to 308.5 mbsf. PCS Core 7P was taken from 308.5 to 309.5 mbsf. Two XCB half-length cores (8X to 9X) were taken from 309.5 to 319.5 mbsf in an effort to obtain better recovery in the suspected hydrate-bearing zone (Hole 995A had 3% recovery at this depth). The two half-length cores had 94% recovery. PCS Core 10P was taken from 319.5 to 320.5 mbsf by pushing in the shoe (no rotation or circulation) and recovered 0.65 m of core. A center bit was used to drill from 320.5 to 410.0 mbsf. Five XCB Cores (11X to 15X) were taken from 410.0 to 456.3 mbsf. The hole was then drilled with a center bit from 456.3 to 700.0 mbsf.

A 35-bbl sepiolite mud sweep was circulated and a wiper trip was made to 100 mbsf to condition the hole for logging. A maximum overpull of 20k lb was encountered pulling out of the hole, with a maximum drag of 40k lb at 530 mbsf while running in. The hole was reamed from 530 to 700 mbsf, with 25 m of fill on bottom. The hole was displaced with sepiolite/seawater mud. The pipe was pulled back to 106 mbsf, and the CSES was rigged.

At 1130 hr on 28 November, the Cape Hatteras arrived on location in order to conduct a two-ship walkaway VSP experiment. The WHOI triaxial vertical seismic profile tool was run and had to be pumped out of the pipe with 250 gpm at 500 psi. The walkaway VSP was conducted for 27.75 hr with the Cape Hatteras. The VSP tool was clamped at 72-m intervals from 680 to 176 mbsf. The Hatteras then conducted a seismic survey in the area before returning to Beaufort, N.C. The pipe was run in to 683 mbsf and a zero-offset VSP was run at 8-m station spacing from 662 to 144 m in 22 hr using the ship's guns. The VSP clamping arm stopped working, and the tool was pulled. A kink was found in the logging cable. About 50 m of logging cable was cut off, the cable was reheaded, and the VSP logs were finished at 0900 hr on 1 December.

A digital dual induction/long-spaced sonic/natural gamma spectrometry (DITE/LSS/NGTC) logging tool was run from 337 to 660 mbsf without the CSES. The pipe was then pulled to 135 mbsf and logging was continued to 135 mbsf. High-temperature lithodensity/dual porosity compensated neutron/natural gamma spectrometry (HLDT/CNTG/NGTC), Geochemical (GLT), and Formation MicroScanner (FMS) logs were run to 660 mbsf without problems. The Lamont Doherty shear sonic tool (SST) was also deployed. Logging required 41.5 hr. Hole 995B was then terminated, the pipe was pulled, and the bit cleared the rotary table on the rig floor at 1150 hr on 3 December.


A 72-km transit was completed in 3.2 hr at 12.2 kt, and a 63-km seismic survey was conducted over Site 996 in 4.8 hr at 7.0 kt. A Datasonics 354M beacon was dropped on GPS coordinates 32°29.629'N, 76°11.480'S. The same APC/XCB drill string was run with a flapper valve and without a monel drill collar. The vibration-isolated television (VIT) frame was run with a television (TV) camera, sonar, a VIT frame beacon, and a deployable beacon. A TV and sonar survey was run from 150 m west to 70 m east of the GPS coordinates. Carbonate crusts were evident over most of the transect, and a chemosynthetic mussel bed was located about 30-50 m east by 10 m north to 10 m south of the GPS coordinates. The seafloor was tagged with the bit at 2169.6 mbsl water depth, and the bit was positioned in the center of the mussel bed.

To Operations Site 996

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