Navis project sails ahead as R&B Falcon raises stake

The hull of the Navis Explorer I is now under construction at the Samsung yard in South Korea, following keel laying ahead of schedule in February.

• Due for delivery in March 2000, the Navis vessel will be capable of drilling in 3,000 meters water depth. [25,896 bytes]

Following keel-laying ahead of schedule in late February, construction of the Navis Explorer 1 deepwater drillship is now into its final 12 months, with delivery due in March 2000.

The vessel is being built at the Samsung yard in South Korea, which is separately building a series of four deepwater drillships for R&B Falcon. Two of these have already been delivered within budget and ahead of schedule. The drilling contractor has become the major shareholder in Stavanger-based Navis ASA, having last year entered into an agreement to operate and manage the vessel.

In connection with these and other design modifications, the US contractor is injecting a further $50 million into the project, in both cash and equipment, which will take its stake to around 38%. Following its arrival, the vessel has been upgraded to drill in 3,000 meters water depth instead of 1,500 meters.

In the light of R&B Falcon's good experience with its other drillships at Samsung, the yard's contract with Navis has been extended to include the topsides fabrication. Previously, this was to be carried out by Hitec, one of the founding members of Navis. Hitec remains responsible for the topside design, which is now being finalized. Also, the firm is supplying specialized equipment, including its Cyberbase drillers control cabin and active heave compensated drawworks.

Navis Explorer 1 is beingbuilt to Norwegian Petroleum Directorate (NPD) requirements, including a double hull and bottom. The NPD standard will enable the vessel to operate anywhere in the world, says Market ing Vice President Per-Allan R sand.

The Navis project incorporates innovative design approaches, but for all vital components only proven technology is being used, according to R sand. As a ship-shape unit, it has a greater deck capacity than a deepwater semisubmersible rig, and hence, an enhanced degree of autonomy. What is unique about the concept, however, is the development of a hull design that gives the vessel motion characteristics equivalent to those of a semisubmersible.

Semi motions

The hull, which was designed by LMG Marin of Bergen, displays a number of features which will reduce the vessel's motions. One of these is a box structure located low down on each side of the hull, and running almost its full length. A second is the fact that the vessel has three moonpools with a total length of more than 70 meters (more than one third of the vessel's overall length), which considerably reduces the waterline area of the hull. Around the bottom of each moonpool side, a box structure is placed. The effect of the box structures, both on the outside of the hull and in the moonpools, is to give negative added mass, which dampens the heave and roll motions significantly, as does the reduced waterline area.

In model tests carried out at the Marintek test basin in Trondheim, the hull behaved very similarly to a semisubmersible hull with respect to both heave and roll, according to R sand. "By reducing the vessel's motions, you increase the weather window in which the vessel can operate," he says, an important point for an oil company keen to find ways of reducing the high costs of deepwater drilling.

Since time is money, drilling efficiency is also a key topic. Here, the emphasis is on state-of-the-art equipment. There is, for example, a dual activity derrick, with an auxiliary rotary table for making up pipe, in addition to the drilling rotary table. "We did a study which showed that there was a 20% increase in efficiency due to the dual derrick," says R sand.

The vessel is 202 meters long and 40 meters wide, and has an operating displacement of 67,500 tons, and a payload capacity of 15,000 tons. The vessel can store up to 10,000 ft of riser and 22,500 ft of drill pipe and casing, and will be able to work for periods of up to 100 days without need of re-supply.

The vessel has ample space for storing equipment for extended well testing, and has an oil storage capacity of 80,000 bbl. For this purpose, a flare boom and offloading facilities can be installed when required. The center moonpool is used for drilling, and the forward and aft ones for ROV deployment. The forward moonpool also could be used for subsea construction or intervention work.

Navis Explorer 1 is currently running within the budget of $290 million, a competitive cost at a time when other similar projects have run into substantial cost overruns.

Market prospects are not what they were when the project was launched, but R sand is not dismayed. He is optimistic that a contract will be secured by the time the vessel is delivered. "The deepwater market has not been hit as much as the shallow water," he says. "Brazil and West Africa are still interesting, and the deepwater Gulf of Mexico perhaps less so. And, the number of players has been reduced."

In the 1,500-meter range, the North Sea also is still showing signs of life. "We know some players that want to change out the old rigs," R sand says. "So, we're not too pessimistic about the market situation. And when the oil price pulls up to $14 a bbl, the market will revive."

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