While the subsea market has taken great strides in the past decade, platform technology has not been neglected. Several new concepts are vying for roles offshore in greater water depths.

By Senior Offshore Editor While the subsea market has taken great strides in the past decade, platform technology has not been neglected. Several new concepts are vying for roles offshore in greater water depths.

Kerr-McGee recently won final approval from the Minerals Management Service (MMS) to use cell spar technology for its Red Hawk development . Red Hawk, located in Garden Banks Block 877 in a water depth of 5,300 ft (1,615 m), is breaking new boundaries; it is the first cell spar in the area, and only the second to use permanent synthetic mooring. The MMS gave the go-ahead after a deepwater operations plan review, which involved comparing the system's buoyancy with that of a conventional spar, examining its response to vortex-induced vibration and inspecting plans for the hull. Technip Offshore is building the spar hull for Kerr-McGee.

This year will see ABB launching results from its 2-year research and development program on NuDeep, its new generation subsea suite designed to tackle deep and ultradeep water depths to 10,0000 ft
(3,050 m) and beyond.

NuDeep will "open the deep, and ultradeep water frontier," said ABB, "moving today's projects that are uneconomical and not technically feasible to develop into the economically viable range."
Second- and third-generation rigs could be utilized on deep fields with this new technology, the company said, and it would permit the use of smaller and lighter intervention vessels for work at greater water depths on deep fields.

Some of the features of the NuDeep program include long-distance transport of hydrocarbons, and subsea processing using a compact coalescer.

ABB declined to discuss its level of investment in NuDeep, or the precise number of personnel committed to the project. "We have passed the research stage," said Rune Stroemquist, group senior vice president for technology research and development within ABB's Oil and Gas division. "We have built 3-D models and simulations on computer. What we are looking for now is a hard project where NuDeep will be suitable. We still have the aim to try and deliver a tender by the end of 2003."

NuDeep will draw on expertise in the following areas: drilling, intervention and completion, structures, pressure containment, manifolds, process and flow assurance, auxiliary systems and overall system design.

The program has two main goals: provide a 20% improvement in development efficiency; and provide a 20% boost to operational efficiency.

The lean market

The semisubmersible rig market has been going through a lean period in the past few years. While work on at least one new design has been stalled, the proponents of the Symrig hope their concept will be realized once the market surges again.

Norway's Marine Technology AS, in collaboration with Navion (now owned by Canada's Teekay Shipping), began working on Symrig in 1998. The five-column stabilized semisubmersible is a huge step away from 30 years of traditional semisubmersible rig designs; it features a five-column alternative to the traditional four-, six- or eight-column configurations. Symrig, its proponent said, is ideal for drilling, production and maintenance functions offshore.

Already US $1.4 million (NKr 10 million) has been spent on perfecting this design, which included model testing at the Norwegian marine research center, Marintech.

However, with the sale of Navion in 2002, and its decision to concentrate on its core business of crude oil transport, Marine Technology has frozen work on Symrig for the time being. "The project is still sleeping due to the general decline in market interest for new semisubmersibles," said Kjell Mork at Marine Technology. "However, we are about to discuss with Navion an agreement that will focus on taking the Symrig design through the final stage of development."

The final stage of development involves scantling approval by Det Norske Veritas, which may take another 6 to 8 months, meaning the design will not be fully matured until the end of this year.
Talks have also been held with Samsung in Korea over the possibility of building a Symrig unit. At the same time, Marine Technology is looking for project partners to take the concept forward.
What are the benefits of the concept? Mjork said Symrig beats a conventional two-pontoon semisubmersible "in every aspect of performance."

Designers threw away all semisubmersible rig-building conventions and started from scratch with a symmetrical hexagonal shape from the baseline through to the upper deck. "This results in a very rigid construction with superior strength properties and impressive operational assets," said the company.
The rig features ample deck space. Because stability is maintained regardless of the direction of prevailing weather conditions, the working environment for personnel is safer. The rig is undergoing extensive testing at Marintech to verify the theoretical analyses of the model. The company is also investigating the hydrodynamic properties of the design.

Enhancing marginal fields

Aker Kværner's deep draft semisubmersible, outlined at an IBC floating production conference late last year, is an enhanced concept for marginal fields. Borre Knudsen and Magne Nygard, of Aker Kværner Technology, and Henrik Hannus of Aker Kværner Inc., outlined the principle behind this recent platform concept. This concept already has been used on the Njord and Snorre B developments in Norway, and on the P51 Marlim Sul and P52 Roncador projects off Brazil.

This design features a deep draft of 85 ft (26 m) to reduce sea motions and includes ring pontoons on the hull (as on the Snorre B unit) and a flat-topped deck (as seen on Njord). The size of the unit is scalable, say AkerKværner, for deck payloads between 2,000 and 8,000 tonnes.

At the same conference, Christian Nygaard of Technip Coflexip outlined the principles for a new dry tree unit, an extendable draft platform (EDP).

Suited to deep water, Technip claims this unit is relatively easy to install, is cost-competitive with other floating production unit concepts, and shortens the time to first oil and peak production. And it minimizes the exposure to offshore risk.

EDP is a three-column design, with a barge-type deck, supported by buoyant columns and a truss structure, plus a pontoon or heave plate at the base.

The design features a low hull steel weight that avoids the need for fixed ballast and provides low horizontal deck acceleration and lower levels of vortex-induced motion.

Hydrodynamic performance tests demonstrate this design can tolerate a maximum offset angle of 164 ft (50 m), pitch of 27 ft (8.2 m) and heave of ±4.59 ft (±1.4 m).

One of the EDP's major benefits is that it is self-installing, Technip said, avoiding the need for a heavy lift vessel. Hook up and commissioning can be completed at dockside. And with its low hull steel weight and lower motions, it is said to be suitable for deep water while remaining cost-competitive with other floating designs.

With a low level of motions, it can support large diameter steel catenary risers. And it provides an extension of known jackup technology, so it has the benefit of not being too revolutionary for the more conservative elements in the offshore marketplace.

Another concept to come out of Norway is the Atlantis artificial buoyant seabed (ABS) concept, developed by Atlantis Deepwater Technology Holding AS (ADTH).

A recent joint-industry project, partly funded by BP and Shell, is working on prototype tests (which were to take place at the end of last month in the Gandsfjord in Norway), where Atlantis will be deployed to its operating depth of 656 ft (200 m).

Altogether, development has cost about $12 million to $14 million, with the latest test phase funded by the Norwegian technology program Demo 2000, BP, Shell and ADTH costing about $7 million. Those marine trials were intended to test towing and deployment of the device, which might be used for deepwater drilling off Angola. ADTH is also looking for deployment in deep basins off India, where more than 50 deepwater wells are planned within the next few years.

"Most of the cost savings come from the fact that you can use second- or third-generation drilling rigs in deep water, combined with taut-leg mooring systems, which can halve the day rates of deepwater rigs," said Paal Norheim, managing director of ADTH.

Atlantis comprises an artificial buoy, which allows subsurface equipment rated only for shallow water between 656 ft and 984 ft (200 m and 300 m) to be deployed on a deepwater drilling project by using a tieback string of the surface casing and connectors from a deepwater wellhead to bring the production flow nearer to the surface. It avoids handling of a long riser, a deepwater BOP, equipment on the seabed and the need for a conductor.

Atlantis is said to offer between 20% and 40% savings on deepwater drilling time and cost, depending on the depth and complexity of the well being drilled.

With an Atlantis ABS in place, drilling operations are the same as for a shallow depth well; the only deepwater requirement is for station-keeping.

During the past years, several oil companies have provided funding for the concept, and in April 2002, Statoil bought a 12% stake in the company.

In the Netherlands, Heerema has been developing its float-over forklift installation barge concept. Conceived for installing 20,000 metric tonnes of topsides on a spar or deep draft caisson vessel, this device uses a "forklift" system attached to Heerema Marine Contractors' H851 launch/cargo barge - named because it is 851 ft (260 m) long.

Providing the forklift element on the barge involves adding two buoyant cantilevered beams to one end of the barge (see Marine Technology column, page 33).

These additional legs are intended to have hydraulic sway/surge connections to dampen the effects of swell, common offshore Brazil and West Africa. With modification, the barge can install topsides with diameters between 90 ft and 155 ft (27 m and 45 m) in high swell regions such as West Africa and Brazil.
Originally, Heerema had a 2004 target delivery date for the complete concept. But further design work is effectively on hold, while the contractor concentrates on other installation opportunities using its existing fleet of barges and heavy lift cranes. Effectively, the float-over is suspended for now, and HMC's undisclosed client has yet to see results from the latest studies. However, it is possible that the concept could be used for installing a compliant tower as part of a Kizomba C project in a water depth of 1,968 ft (600 m) offshore West Africa.

Meanwhile, HMC has extended its deepwater installation capability in another direction by adding a new hammer spread - an offshore pile-driving capability ordered from Germany's Menck - which became operational this month. In 2002, Menck installed 10 84-in. diameter and 259-ft (80-m) anchor piles in water depths ranging from 2,106 ft to 2,333 ft (642 m to 712 m) in Mississippi Canyon Block 582, for Murphy Oil's Medusa project.

"Having our own hammer spread means we are not only able to meet client's requirements for installation, but when tendering for new work, we are confident that the hammer is available," said HMC's Chris de Ruiter.