SITE 1045
(Proposed Site NBR-8A)

The vessel was offset in dynamic positioning mode at a speed of 2 nmi/hr from Hole 1044A to Site 1045 while retrieving the BHA and downloading the LWD data from Hole 1044A. The distance between NBR-8A and NBR-9A is ~1 km, and one beacon was dropped between these sites and used for operations at both sites. LWD Hole 1045A was located at GPS coordinates 15°32.2407'N and 58°43.4222'W. After changing out the LWD tools, the same BHA from Hole 1044A was assembled with a new Smith 9-7/8 in FDGH (3x14) bit. Hole 1045A was spudded at 1445 hr 30 December 1996. Drilling was initiated at a water depth of 4980.4 mbrf based on the PDR reading. As at all the LWD sites, it was not possible to determine the mudline with the drill pipe in the soft sediments. Therefore, the PDR reading of 4980.4 mbrf was used for the initial water depth. The final water depth was established at 4982 mbrf (4971 mbsl) based on the analysis of the LWD data.

We attempted to drill at 35 m/hr down to 5416 mbrf (434 mbsf) where high pump pressure and torque were encountered. The décollement zone was estimated at 424 mbsf and considerable back reaming and hole conditioning were required to advance the drill string beyond this point. The drill string was pulled up to 5371 mbrf (389 mbsf) and a 30-bbl sepiolite mud sweep was pumped. The hole was then reamed back down from 5371 to 5416 mbrf (389 to 434 mbsf). Drilling continued down to 5468 mbrf (486 mbsf) where the hole packed off and high pump pressures and torque were encountered. Rotation was required to pull the drill string back up the hole and 30,000 lb of overpull was encountered.

A request was made to ODP/TAMU for permission to deepen Site NBR-9A by 250 m from 600 to 850 mbsf to achieve the deeper depth objectives below the décollement (underthrust section), which we suspected could not be achieved at Hole 1045A. Permission was granted from ODP/TAMU for an additional 250 m (+25 m) penetration or first contact with basement at Site NBR-9A. Because the total time on the LWD tool batteries was approaching 48 hr and they can provide power for a maximum of ~100 hr, the decision was made to abandon Hole 1045A and offset in DP mode over to Site NBR-9A. The remaining time would allow Hole 1046A to be drilled without having to trip the drill string which would result in a time savings of approximately 20 hr. The drill string was pulled out of the hole, and the seafloor was cleared at 1945 hr 31 December ending Hole 1045A. The drill string was pulled an additional 50 m above the seafloor, and the vessel was offset in DP mode over to Site NBR-9A.

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