After completing drilling at Site 899, we moved the ship to 40°41.00'N, 11°36.25'W, Site 900 (IAP-5), and deployed a Datasonics beacon. The precision depth recorder indicated a water depth of 5045.4 mbsl. 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) having a mechanical bit release (MBR) was assembled and run to the seafloor. The bit was positioned at 5048.5 mbrf, and Hole 900A was spudded at 0605 hr Universal Time Coordinated (UTC), 11 May 1993, by advancing 1.5 m. From Core 149-900A-1R, 1.36 m was recovered; therefore, the seafloor was assigned a depth of 5048.5 mbrf. Cores 149-900A-1R to -86R were taken from 5048.5 to 5853.5 mbrf (0-805.0 mbsf; Table 1), with 805.0 m cored and 519.61 m recovered (65% recovery). The first three cores were taken without rotating or pumping seawater; the weight-on-bit, rotation speed, and pump rate gradually were increased in response to increasing formation hardness and for maintaining good hole conditions and core recovery. The water sampler and temperature probe (WSTP) was successfully run at 5170.9 mbrf (122.4 mbsf), 5219.1 mbrf (170.6 mbsf), and 5267.3 mbrf (218.8 mbsf).
We conducted two wiper trips in the sedimentary section. The first was after Core 149-900A-39R, when we moved the pipe between 5412.0 to 5196.6 mbrf (363.7-148.1 mbsf). A second wiper trip was made after Core 149-900A-75R, when we moved the pipe between 5758.8 and 5600.0 mbrf (710.3-551.5 mbsf). We encountered a bridge at 5747.0 mbrf, washed and rotated the bit past it to total depth, and found no fill in the bottom of the hole.
Metamorphic basement rocks were encountered at 748.9 mbsf. After Core 149-900A-86R (805.0 mbsf), suspecting imminent failure of the bit, we decided to stop coring and prepare for logging. The hole was circulated clean, and a short trip was made to 5187 mbrf. Minor overpull was observed while pulling up, and the tight sections were reamed out while moving the pipe down. We then circulated clean the 10 m of fill at the bottom of the hole. The bit was released, and the end of the pipe was pulled to 5185.4 mbrf (136.9 mbsf) for logging.
Two logging runs were made. During the first run (dual induction tool [DIT], caliper tool [MCD], dipole shear imager [DSI], and natural gamma-ray spectrometry tool [NGT-C]), the tool would not pass 5286 mbrf (237.5 mbsf). The drill pipe was repositioned at 5378.5 mbrf (330.0 mbsf). No obstructions or drag were noted while running the drill string farther into the hole. The first logging combination was rerun; however, it would not pass 5500 mbrf (451.5 mbsf). After the logs were run, we pulled the drill pipe up to 5244 mbrf (195.5 mbsf) and picked up the conical side-entry sub (CSES).
A tool combination that included the Formation Microscanner (FMS) and NGT-C was loaded into the CSES, and the drill string was run to 5802.2 mbrf (753.7 mbsf); however, the tool would not pass 5837 mbrf (788.5 mbsf). The pipe was pulled up to 5742 mbrf (693.5 mbsf) in an effort to get above the collapsed hole. The combination was rerun from 5837 to 5695 mbrf (788.5-646.5 mbsf). The tool became stuck at 5695 mbrf (646.5 mbsf). The drill string was washed down to 5698 mbrf (649.5 mbsf) over the stuck tool. The logging tool came free, and the drill string and tool were pulled to 5528.9 mbrf (480.4 mbsf). This combination was run again and became stuck at 5613 mbrf (564.5 mbsf). We washed the drill pipe over the tool from 5528 to 5614 mbrf (478.5-565.5 mbsf). At this point, we abandoned logging be cause of poor hole conditions and damage to the logging cable and FMS tool. We recovered the drill string, recalled the two beacons, and terminated operations at Site 900 at 1518 hr, 22 May 1993.