When the survey was concluded, a beacon was dropped on the prospectus site GPS coordinates at 1200 hr. The corrected PDR depth referenced to the DES was 5592.4 m. A nine-collar BHA was made up of a new C-7 four-cone rotary bit, a mechanical bit release, a head sub, an outer core barrel, a top sub, a head sub, seven 8 1/4-in drill collars, one tapered drill collar, six 5 1/2-in drill pipes, and one crossover sub. Although no logging was anticipated, the mechanical bit release was affixed to free the BHA should the drilling assembly become stuck at the bit.
Hole 1153A was spudded with the RCB at 2300 hr on 29 November. The
bit tagged seafloor at 5592.4 m. The drill string was washed ahead with a
core barrel in place to 267.6 mbsf, where basalt was contacted. During the
process of washing ahead without coring, seven wash barrels were
recovered from 26.9, 142.3, 151.9, 209.6, 233.4, 243.0, and 267.6 mbsf.
The last wash barrel recovered some basaltic rock, so we began rotary
coring. We experienced unstable hole conditions while washing from 243
to 268 mbsf. This condition required redrilling the bottom of the washed
interval. When the drill string was pulled back to 248 mbsf, the driller
noted ~40,000 lb of drag at 253 mbsf.
Prior to initiating rotary coring, the core barrel was dressed with a "whirl-pak" bag containing fluorescent microspheres as a circulating fluid contamination tracer. Before coring could be initiated at 268 mbsf, the driller had to ream the hole again from 248 to 268 mbsf. The hole was then flushed with a sepiolite mud treatment. The interval 267.6-274.9 mbsf was cored, but the hole became unstable again as 7 m of fill was encountered after we recovered the core barrel. The poor downhole conditions suggested a low probability that the hole could be deepened further, so coring was terminated. The drill string was recovered; the bit cleared the seafloor at 1030 hr and cleared the rotary table at 1630 hr on 1 December. The vessel was under way to the next site by 1900 hr on 1 December.
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