OPERATIONS SYNOPSISTransit to Site 1184
We spudded Hole 1184A with the rotary core barrel (RCB) at 2000 hr on 1 October. The bit tagged the seafloor at a depth of 1661.5 mbsl. We drilled ahead without coring to 134.4 mbsf at an average rate of penetration of 67 m/hr. After retrieving the wash barrel, we dropped another core barrel and began rotary coring. Hole 1184A was rotary cored from 134.4 to 326.6 mbsf with an average recovery of 76.3%. We contacted acoustic basement at 201 mbsf; it consisted of volcaniclastic rocks. The average recovery for acoustic basement was 77.1% (96.4 m recovery). The average penetration rate in acoustic basement was 2.5 m/hr.
After coring to 326.6 mbsf, the bit had accumulated 54 rotating hours, and we decided to change the bit. A 50-bbl sepiolite mud flush was circulated in the hole and the bit pulled back to 142 mbsf. Following the successful deployment of the second FFF of the leg, we observed the withdrawal of the bit from the top of the FFF with the VIT. Most of the FFF was covered by sediment, but the three glass floats were clearly visible. The used bit cleared the rotary table at 0800 hr on 5 October. An inspection of the bit found that it was, remarkably, in nearly pristine condition with no visible wear evident except a slight rounding of the chisel inserts on the cones. The crew removed the old bit and mechanical bit release and replaced these with a new RBI C-7 harder formation bit and a new mechanical bit release.
We successfully reentered Hole 1184A at 1400 hr on 5 October after a 30-min search. The
drill string was run in to 238 mbsf, where the driller observed 20,000-30,000 lb of drag. After the
top drive was picked up, the drill string became stuck in the formation. Fortunately, circulation was
never lost, and the pipe came free after applying 200,000 lb of overpull above the weight of the
drill string. Routine hole maintenance was conducted by washing and reaming the hole from 238
to 326 mbsf. We resumed coring operations in Hole 1184A at 1730 hr on 5 October. The interval
from 326.2 mbsf to 538.8 mbsf was cored at an average rate of penetration of 4 m/hr and 86%
average recovery. We terminated operations in Hole 1184A when the time allocated for this site
had expired. After the crew retrieved the drill string, recovered the beacon, and retracted the
thrusters and hydrophones, we began the transit to Site 1185 at 0530 hr on 9 October.
The cored interval in Hole 1184A was 404.4 m with 328.8 m recovered (81.3%) and an average penetration rate of 3.8 m/hr. Apart from the momentary sticking of the drill string following the bit change, we encountered no hole problems.
Site 1185 | Table of Contents