The drill bit was positioned at 1986 mbrf for the initial core, and an 8-m core established seafloor depth at 1987.5 mbrf. Continuous APC coring continued through Core 20H. Good environmental operating conditions permitted very good core recovery despite several core liner failures, but the weather began to deteriorate as TD was approached.
Withdrawal overpull on Core 19H was 30 kips, but Core 20H (188.5 mbsf TD) could not be pulled free with a force of 100 kips. It was necessary to drill over the core barrel for 5 m to free it. Vessel heave had increased to nearly 2 m by that time, and the APC assembly sustained severe damage from the drillover operation. Coring operations were terminated because most scientific objectives and effective APC refusal had been reached.
The ship was offset 10 m laterally. To achieve stratigraphic overlap, the new hole was spudded with the bit 4 m higher than for Core 1092A-1H. Core recovery indicated a seafloor depth about 3.5 m shallower than at Hole 1092A. Weather and motion conditions were less favorable for Hole 1092B, and core recovery and quality were diminished by an increase in core liner failures and other motion-related factors. Overall recovery was good, but there were gaps in the recovered section. The coring depth target was reached with Core 18H at 168.9 mbsf, and the drill string again was withdrawn for a respud.
Coring began at 2115 hr on 8 January. Results improved with time and depth as the weather abated and vessel-motion conditions improved. The target depth of 165.5 mbsf was reached after 18 cores.
The first three holes at Site 1092 had failed to achieve complete stratigraphic coverage of the section because of lost and disturbed cores at a relatively shallow depth. Thus, a fourth hole was requested to cover the interval equivalent to 36-64.5 mbsf in Hole 1092C.
When the bit had been pulled clear of the seafloor, the vessel was offset to a position near the center of the three positions determined for the first three holes. The new positioning offsets were closest to Hole 1092B and, therefore, the seafloor depth of that hole was assumed. Hole 1092D was spudded at 0840 hr on 9 January and the hole was drilled ahead to 36.4 mbsf. From there, three consecutive APC cores were taken to a TD of 64.9 mbsf. Coring results were good and the scientific objectives of the site were achieved.
The drill string was recovered, and the bottom-hole assembly (BHA) connections were inspected magnetically for cracks. The vessel was under way at 1818 hr on 9 January.
To 177 Operations - Site 1093
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