Sonat Offshore's drillship Discoverer Enterprise, scheduled for completion in the first quarter of 1998, will be far larger than any other drilling unit in the offshore business. The dynamically positioned drillship will be 850 ft in length and 140 ft in width. Today, the longest drillship is 530 ft long and 80 ft wide.
Size is critical to the drillship's enhanced functions, not only because it raises the variable deckload substantially and allows the ship to minimize weather downtime, but provides for something not previously seen because of space limitations. The unit will have multiple functions on the extended drilling deck, which will be 80 ft by 100 ft compared with the conventional 40 ft by 40 ft deck.
For example, a modified derrick and drill floor will allow for the makeup of drillstring and bottom hole assemblies separate from the drilling line where other functions such as casing installation may be underway. Simultaneous functions allow for 20-40% faster tripping of drillstrings.
Until drilling contractors pursued drilling in depths beyond 4,000 ft, multi-functionality did not provide a suitable economic return for the size vessel drilling platform required. With consistent drilling in deepwater, tripping of drillstrings takes up as much time as turning the drill bit.
The Discoverer Enterprise is so large, it is conceivable that the hull could be set up for two drilling masts and drillfloors. Now that extended reach and horizontal drilling is so well developed, such a dual capability would be useful for speeding up field development drilling. At this time, Sonat has no plans for such a change.
In early June, Sonat had not decided whether to build a completely new ship or purchase a tanker from Finland. In any case, the ship will feature a double hull. Sonat's plans are to equip the vessel with six 2,000 ton drilling packages in Galveston, Texas. Initially, the unit will be able to drill in 7,000 ft of water, but will have the ability to deal with 10,000 ft depths.
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