After completing drilling at Site 898, the ship was moved 8 nmi (15.7 km) northwest to Site 899. We deployed a Datasonics beacon at 40°46.34'N, 12°16.07'W. This location had been confirmed during the geophysical survey prior to the mid-leg Lisbon port call (end of Leg 149B). After the ship was stabilized in dynamic positioning mode over the primary beacon, a second backup Datasonics beacon was deployed.
A rotary core barrel (RCB) bottom-hole assembly (BHA) was assembled and run to the seafloor. The vibration-isolated television (VIT) was lowered, and the seafloor was observed at 5302.5 mbrf. A jet-in test was conducted from the seafloor to 5366.5 mbrf (0.0-64.0 mbsf), beyond which depth we were unable to penetrate. We then drilled from 5366.5 to 5384.0 mbrf (64.0-81.5 mbsf). Cores 149- 899A-1R to -16R were taken from 5384.0 to 5538.0 mbrf (81.5- 235.5 mbsf; Table 1). Well-compacted clay was cored at 5512.5 mbrf (210 mbsf); we stopped coring at 5538.0 mbrf (235.5 mbsf) to set a reentry cone, 49.6 m of 16-in. casing, and 216 m of 11.75-in. casing.
The ship was moved 20 m north to 40°46.347'N, 12°16.063'W. We assembled three joints of 16-in. casing (49.62 m) with a three-cone drill bit inside the casing about 0.15 m above the shoe and attached it to a reentry cone. The reentry cone and casing were run to the seafloor, where the casing was jetted-in to 5352.1 mbrf (49.6 mbsf), placing the reentry cone on the seafloor. The drill bit was disconnected from the casing, and we drilled to 5529.5 mbrf (227.0 mbsf). The hole was filled with a mixture of sepiolite clay and seawater, and we pulled out of the hole.
We assembled 216 m of 11-3/4-in. casing and lowered it to 5518.9 mbrf (216.4 mbsf). The casing was cemented in place. After pulling out of the hole, we assembled an RCB-BHA having a chisel point center bit and mechanical bit release (MBR) and lowered it to the seafloor. We reentered the hole, encountered cement at 5508.0 mbrf (205.5 mbsf) and drilled through the cement and the 11-3/4-in. casing shoe. A 4.5-m section of new hole was drilled to 5533.0 mbrf (230.5 mbsf) to break down completely pieces of the shoe.
Cores 149-899B-1R to -37R were taken from 5533.0 to 5865.0 mbrf (230.5-562.5 mbsf), with 332.0 m cored and 173.41 m recovered (Table 1). Hard rock (acoustic basement) was encountered at 369.8 mbsf. Below Core 149-899B-26R (464.2 mbsf), recovery decreased (to less than 20%) and hole conditions deteriorated. We discontinued coring at 557.6 mbsf because of high torque, overpull, and continuous sloughing of material into the bottom of the hole.
The hole was reamed from 5764.0 to 5860.1 mbrf, and Core 149-899B-37R was taken from 5860.1 to 5865.0 mbrf (557.6-562.5 mbsf), with 4.9 m cored and 0.19 m recovered. Hole conditions remained poor, and we again attempted to ream and wash the hole from 5505.0 to 5865.0 mbrf (202.5-562.5 mbsf). We encountered several bridges that had to be drilled through (a wash barrel was recovered from this section). Finally, the pipe became stuck at 5852.0 mbrf (549.5 mbsf) and after pulling free with difficulty, we decided to terminate coring at Site 899B.
The original plan for logging at Hole 899B was to drop the bit on the seafloor. Because of the unstable hole conditions, the importance of logging the peridotite basement, the risk of the hole collapsing should the drill string be pulled out of the hole to drop the bit, and the probability that an open-ended drill string could not be worked back down below the top of basement to obtain logs in the basement, we decided to release the bit in the hole.
The bit was released using the MBR at 5841.6 mbrf (539.1 mbsf). The open drill string was pulled to 5696.3 mbrf (393.8 mbsf), which was just below the top of the peridotite breccia at 369.8 mbsf (for details of the logging operations see "Downhole Logging" section, this chapter). The first two logging runs (Run 1 = dual induction tool [DIT], caliper tool [MCD], dipole shear imager [DSI], natural gamma-ray spectrometry tool [NGT-C], and the Lamont temperature logging tool [TLT]; Run 2 = slim-hole lithodensity logging tool [HLDT], dual porosity compensated neutron tool [CNT-G], sonic digital logging tool [SDTC], NGT-C, and TLT) were successfully run to 5757.0 mbrf (454.5 mbsf) and 5747.0 mbrf (444.5 mbsf), respectively. The neutron source of the induced gamma-ray spectrometry tool (GST-A) malfunctioned during our initial attempt at the third logging run (GST-A, aluminum activation clay tool [ACTC], CNT-G, NGT-C, and TLT). We replaced the GST-A source and the logging run was made. Although the neutron source failed again, we continued logging with the remaining tools in this combination to 5737.0 mbrf (434.5 mbsf). During this run, sediment had accumulated in the bottom of the hole, which decreased the amount of section that was possible to log; thus, we decided to discontinue logging this interval. The drill string then was pulled up to 5496.5 mbrf (194 mbsf), inside the casing, and we made a fourth logging run with the Formation Microscanner/NGT-C/TLT combination tool. This tool was unable to penetrate more than 4 m below the end of the casing, and logging was terminated. The drill pipe was pulled out of the hole, and the two beacons recalled and recovered.