After finishing operations at Site 1116, we began the transit to Site 1117 in dynamic positioning mode. During the transit, an RCB coring BHA with a MBR was assembled. Because the seafloor at Site 1117 was expected to be exposed metamorphic rocks with minimal talus, we used a C-7 core bit that was expected to do better in these harsh drilling conditions. As at earlier holes, the mechanical drilling jars were verified to be in good working condition and included in the BHA. The drill string, with a core barrel in place, was lowered to a depth of 1113.3 mbsl. While the pipe was being lowered to the seafloor, the positioning beacon was deployed at 1205 hr, and the ship was positioned over the site.

SITE 1117

Hole 1117A

The drill pipe was gently lowered until the bit encountered the seafloor at 1163.2 mbsl and we spudded Hole 1117A at 1535 hr on 26 July. Because hard rock was exposed at the seafloor, the first cored interval extended to 12.2 mbsf. This allowed the driller to maintain some rathole below his bit so that the bit would remain in the hole when recovering the first core barrel and making the next drill pipe connection. As on earlier attempts during this leg to spud directly into hard seafloor, initial progress was slow and it took >6 hr to cut the first core. The result was remarkable, with 4.07 m intact fault gouge being recovered. The success proved to be short-lived however, when an additional 13 cores recovered a total of 2.35 m (2.4%). Because of the hard, highly fractured formation and the poor recovery, it was thought that this hole was living on borrowed time almost from the start. It was pretty clear to everyone that once the drilling jars and the top of the BHA (8 1/4-in drill collars) became buried below the seafloor, 97.2 and 115.5 m respectively, the real problems would begin. The likelihood of the hole penetrating much below 100 mbsf was slight. Sure enough, at 0215 hr on 28 July 1998, while cutting Core 14R at 111.1 mbsf the driller began to experience excessive drilling torque. The pipe was pulled back to a depth 50.1 mbsf with 60,000 lb overpull. At that point rotation was lost and the pipe became firmly stuck. The pipe was worked for 15 min with up to 200,000 of overpull before rotation was regained and the pipe became free. We all knew that once these problems began it would be a diminishing return of penetration gained over time spent. Therefore, the bit was pulled clear of the seafloor at 0400 hr on 28 July. Total recovery for Hole 1117A was 6.42 m (5.8%).

 Hole 1117B

Because of the keen interest in attempting to obtain another surface core containing fault gouge that could be used for whole-round sampling, we decided to cut another "mudline" core. Without offsetting the ship, Hole 1117B was spudded at 0445 hr on 28 July. The bit tagged the seafloor at the same depth as Hole 1117A (1163.2 mbsl). Core 1R was cut in 3.5 hr to a depth of 9.5 mbsf. The bit was pulled clear of the seafloor at 0830 hr. When Core 1R was recovered, it did not contain any fault gouge and only 5 cm of metamorphic rock.

Hole 1117C

We decided to make one more try to obtain more fault gouge. Again without offsetting the ship, Hole 1117C was spudded at 0900 hr. Core 1R took <2.25 hr to advance to 9.5 mbsf. The bit was pulled clear of the mudline and the core barrel was recovered. Core 1R recovered only 10 cm of metamorphic rock and, unfortunately, no fault gouge. The rig crew began to retrieve the drill string; the positioning beacon was recovered at 1245 hr on 28 July, and the ship began the transit to Site 1118 (proposed site ACE-1C).


To 180 Site 1118

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