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doi:10.2204/iodp.proc.302.106.2006

Concept

Overall, the approach developed by the ADPG and refined by SPRS was relatively simple. In the three-ship operation (Fig. F2), the nuclear icebreaker would first manage the oncoming ice by breaking the large floes into smaller floes. If the nuclear icebreaker was not able to “manage” a floe, drilling would have to be suspended and the drill pipe tripped to the seafloor until the floe passed.

The nuclear icebreaker would have to operate at a distance far enough (~500 m–1 km) upstream so that there would be enough time to trip the drill pipe and move the drillship away from any “unbreakable” oncoming floes. At the same time, a second, more maneuverable icebreaker would work between the nuclear icebreaker and the path to the drillship, reducing the size of the ice floes and keeping the drillship relatively free of ice so that it could maintain station in DP mode.

The ice management plan included Radarsat images to provide an overview of conditions, helicopter reconnaissance to map the local ice field near the drill sites, an onboard weather observation team, and real-time monitoring of ice speed and direction using ice-based monitoring equipment. With this suite of tools, the ice management team would be able to forecast ice conditions in a 24–48 h window.

SPRS recognized the critical importance of ice and fleet management and defined a critical position for the expedition, the Fleet Manager, responsible for leading the overall operations.

SPRS, in planning the fleet and ice management, made conservative estimates on the length of time that the drillship would be able to maintain station. Their estimate was ~48 h. They viewed this estimate as workable based on time estimates for coring and logging calculated by Seacore, who had updated estimates made by the proponents in Proposal 533. The British Geological Survey (BGS) coring operation estimates were as follows:

• Pipe trips: 5–6 h in 1200 m of water,

• Piston coring: 4.5 m of core recovery every 50 min, and

• Extended/Rotary coring: 4.5 m core recovery every 70 min.

These estimates equate to a total of 9.2 days for tripping pipe, double-coring the upper 400 m, logging one hole, and temperature measurements in one hole. Seacore further estimated that if a third hole were required to core 100 m into basement (and assuming a pipe trip was needed to change the bottom-hole assembly [BHA]), the added time would be 57 h. This estimate was based on being able to wash ahead at a rate of 20 m/h.

SPRS’s ice management protocols incorporated T-time estimates. T-time was the time required to trip or recover the pipe from the hole so that the ship would be free from the seabed and could move under heavy ice forces. If ice management could not achieve a good ice condition window longer than the T-time, drilling operations would be suspended by tripping pipe out of the hole.

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