We spudded Hole 1140A at 0315 hr on 23 January 1999. The seafloor depth adjusted to the rig floor was estimated at 2406.0 m based on a hard "tag" indication by the driller. The 3.5-kHz PDR had indicated an adjusted seafloor depth of 2410.4 m.
Continuous wireline coring proceeded in diatom-bearing nannofossil ooze and a foraminifer bearing nannofossil ooze through Core 14R to a depth of 131.4 mbsf. Recovery was problematic. Low circulation rates led to core jamming, and increased circulation rates tended to wash the material away. Recovery for this interval averaged 26.3%, and the average ROP was 33.8 m/hr. The formation then graded into nannofossil chalk to a depth of 237.3 mbsf. The average recovery improved through this interval to 65.2%, whereas the average ROP dropped to 24.7 m/hr. At the base of Core 25R, the first igneous rock was recovered. Based on the driller's measured depth, the top of igneous basement was estimated to be at ~234.0 mbsf. Coring continued through pillow basalts with glass rims to a TD of 321.9 mbsf. The penetration rate varied from 0.9 to 4.9 m/hr. The average ROP in basement was 2.0 m/hr. Recovery in basement also varied considerably, ranging from 0% to 111% and averaging 52.0%. Coring was terminated with the recovery of Core 37R from a depth of 321.9 mbsf, ~88 m into basement. Coring was suspended to leave enough time for wireline logging and still depart the site no more than 1 day behind schedule. A total of 144.86 m of core was recovered at this site for an overall average of 45.0%. Recovery in basement was slightly better at 52.0%.
During the coring operation, 20-25 bbl of sepiolite mud sweeps were initiated once igneous rock was reached and they were consistently pumped during every core. A wiper trip was made to a depth of 90.2 mbsf to prepare the hole for wireline logging. No problems were encountered during the wiper trip, and no drag or overpull was noted by the driller. On bottom, the hole was swept with a 30-bbl sepiolite mud pill, and the bit was released. The hole was then displaced with sepiolite mud, and the end of the pipe was placed at a depth of 98.5 mbsf for logging.
The wireline logging program at this site was very successful. The first logging run included the DIT-E, HLDS, APS, HNGS, and the LDEO TAP. This run was successful in reaching the bottom of the hole at ~322 mbsf. Because of downhole computer failure, the TAP data were lost. The next run was with the FMS and LSS tools. An NGT was included for calibration between runs. This deployment was also successful in reaching the bottom of the hole. Two passes were made in basement (~88 m). The third run was with the well seismic tool (WST). This tool was also successful in reaching the bottom of the hole. Seismic check shots were completed at 10-m intervals in basement, and two stations, at 149 and 109 mbsf, were completed in the sedimentary column. The logging data showed a maximum 5° hole deviation. Contrary to our experience at earlier sites, the weather remained good for the logging operation. By 1815 hr on 27 January 1999, the logging line and sheaves were rigged down, and the remaining pipe trip was tripped out of the hole. We cleared the seafloor at 1845 hr. While the drill string was being tripped, the positioning beacon was released and recovered. The mechanical bit release reached the rig floor at 0320 hr. By 0330 hr the ship was secured for transit, and we immediately got under way for Site 1141.
Leg 183 Operations - Site 1141
Leg 183 Table of Contents