161 Preliminary Report

Site 974

We deployed a Datasonics 354M beacon at 40°21.3'N, 12°08.59'E on 0345 hr, 7 May. This is the location of Site 652, which was drilled during ODP Leg 107. We then deployed a second beacon about 175 m northwest of the first beacon. The first beacon was turned off and used as a backup. The ship was positioned over the second beacon, due to concerns of the scientific party that the borehole might be too close to the existing Site 652 tailings.

Unless otherwise noted, depths in the operations section within individual site reports refer to meters below rig floor (mbrf). This depth is calculated using drill pipe measurements (DPM) from the top of the dual elevator stool (DES) on the rig floor. The DES is approximately 10.9 m (10.86 m for Holes 974A, 974B, and 974C; 10.89 for Hole 974D) above sea level and varies over time depending on the ship's draft. The seafloor depth, and therefore the depth below seafloor (mbsf) from which cores are recovered, are calculated using the recovery of the mud-line core at each hole, the DPM, and the elevation of the DES above sea level.

Hole 974A

Two APC/XCB holes to 200 mbsf and a third APC hole to refusal were planned for Site 974. An APC/XCB bottom hole assembly (BHA) was assembled and used during the entire leg for the APC/XCB holes. It consisted of (1) an 11-7/16-in. Security roller cone bit (S/N 478458), (2) a bit sub (BS), (3) a seal bore drill collar (SBDC), (4) a landing saver sub (LSS), (5) a long top sub (LTS), (6) a head sub (HS), (7) a nonmagnetic drill collar (NMDC), (8) five 8-1/4-in. drill collars
(DC), (9) a crossover sub (XO), (10) a 7-1/4-in. DC, (11) a crossover sub (XO), (12) five joints of 5-1/2-in. drill pipe (DP), and (13) a crossover sub (XO).

A "rabbit" was passed through all of the drill pipe to ensure that the core barrels would pass smoothly through the DP. Five stands of 5 in. drill pipe were not used because the "rabbit" would not pass. The DP was then measured with a steel tape measure (SLM) as it was added to the drill string. Once assembled, a wiper "pig" was pumped through the pipe and onto the seafloor to clean the inside of the DP of rust and lubricant used on the pipe connections.

Hole 974A was spudded at 1630 hr, 7 May at 40°21.364'N, 12°08.506'E. The corrected precision depth recorder (PDR) indicated a water depth of 3474 mbrf. Core 161-974A-1H was taken with the bit at 3470.0 mbrf. Core 161-974A-1H, however, was full (9.81 m recovered; 103% recovery), indicating that we missed the mud line, and an exact seafloor measurement can only be assumed. Notes from the driller indicated that we may have lowered the bit into the seafloor by as much as 5 m before we shot Core 161-974A-1H. Since we missed the mud line, Hole 974A was terminated and the bit cleared the seafloor at 1700 hr, 7 May.

Hole 974B

We raised the drill string from 3469.7 to 3462.0 m, and spudded Hole 974B at 1730 hr, 7 May. Core 161-974B-1H recovered 6.78 m of sediment; therefore, the seafloor was defined to be at 3454 meters below sea level (mbsl). Cores 161-974B-1H to -18H were taken from 0 to 165 mbsf (3630 m) and recovered 172.73 m (105% recovery). We oriented Cores 161-974B-3H to -18H using the Tensor tool.

Coring was interrupted for about 3.5 hr when one of three strands of the sand line parted at the oilsaver while going in to retrieve Core 161-974B-11H. Approximately 1050 m of sand line was removed from the aft sand-line drum, and the forward sand line was used during the remainder of Site 974.

Overpull (up to 40,000 lb) started at Core 161-974B-16H, and partial bleed-off indicated that there may have been a partial stroke. A partial stroke of about 6.5 m was inferred for Core 161-974B-18H from the fact that both the pressure had to bleed off and that the driller raised the drill string 3 to 4 m before observing any resistance. Once retrieved on deck, we observed that the liner of Core 161-974B-18H was splintered for almost its entire length, most likely the result of a hard impact with the bottom of the borehole.

We started XCB-coring at 3630 m (165 mbsf) after drilling out the 6.5-m rat hole created by
Core 161-974B-18H. XCB Cores 161-974B-19X to -22X were taken from 165 to 203.7 mbsf, with 38.7 m cored and 35.5 m recovered (92% recovery). The combined APC/XCB recovery for Hole 974B was 102%.

Having reached the depth objectives, we terminated Hole 974B, and the bit cleared the seafloor at 2345 hr, 8 May. Hole 974B was completed in a total of 30.75 hr.

Hole 974C

We offset the ship 50 m southeast and spudded Hole 974C at 0115 hr, 9 May, with the bit at 3459.0 m. Core 161-974C-1H recovered 4.36 m; therefore, the seafloor was defined to be at 3453 mbsl. Cores 161-974C-1H to -16H were taken to 146.8 mbsf (3611 m) and recovered 153.91 m (105% recovery). We stopped APC coring one core earlier than in Hole 974B in an attempt to prevent the liner from shattering and disturbing the core. ADARA temperature measurements were taken during Cores 161-974C-3H, -6H, -9H, -12H, and -15H. All ADARA measurements were successful. There was no indication of any significant frictional heating due to tool movement.

XCB Cores 161-974C-17X to -22X were taken from 156.4 to 204.5 mbsf (3611 to 3668.7 m), with 57.7 m cored and 45.94 m recovered (80% recovery). Flow ports in the XCB shoe continued to become clogged in the clay; however, except for Core 161-974C-17X, recovery was good.

The hole was conditioned for logging with a short wiper trip. No drag and only 6 m of
sediment fill in the bottom of the hole indicated that conditions were good for logging. The
hole was displaced with seawater. No KCl or bentonite mud was used. The bit was positioned
at 63.36 mbsf (3527.56 m) to log. The bit was raised approximately 20 m (to ~43 mbsf) before the logging tools reentered the drill pipe to allow more of the upper borehole to be logged. The quad-combo tool was run first, then the FMS tool, and finally the GLT. The logs were run to 3662, 3625, and 3656 mbrf, respectively. No significant operational or hole stability problems were reported. The logs indicated that hole angle was about 1.5°, and the hole diameter ranged from 12 to at least 15 in. We finished logging at 2045 hr, 10 May, and the bit cleared the seafloor at 2100 hr, 10 May.

Hole 974D

We offset the ship 25 m to the northwest and spudded Hole 974D at 2245 hr, 10 May. The scientific party requested that the interval from 4 to 8 mbsf be recovered within a single core to fill in gaps from the previous holes. The bit was positioned at 3457.0 m, and Core 161-974D-1H recovered 1.64 m; therefore, the seafloor was defined to be at 3454.0 mbsl. Cores 161-974D-1H to -18H were taken to 163 mbsf (3628 m) and recovered 170.49 m (105% recovery). The beacons were released (1300 hr and 1510 hr, 11 May, respectively) and recovered (1420 hr and 1600 hr, 11 May, respectively). The BHA cleared the rig floor and was secured for transit at 1930 hr,
11 May, and the transit to proposed site MedSap-6A began at 1930 hr, 11 May.

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