With 37 units built, the Aker H3 design has been in use for 30 years and is the most successful semisubmersible in the offshore industry.

Aker has decided to build upon that success by offering a new and, it hopes, better version. The Aker H4.3 builds on the design of the H4.2 semisubmersible platform to provide the industry with a 21st century drilling system.
"Thirty-seven H3s have been built. There is no other design...I cannot think of any further design of which more than four, five or six have been built," said an Aker spokesman.
Magne Nygård is leading the team developing the new rig. But it exists only on paper and as computer models. "It is a concept," said Nygård. "There is no detailed design engineering so far. It is concept we are ready to enter a contract on."
Several variations of the Aker H4.3 have been developed. One version is for ultradeepwater operations, with dynamic positioning capable of operating in 10,000-ft (3,048-m) waters. Another version will be equipped for drilling in water depths to 1,640 ft (500 m). This will be a harsh-environment unit, specifically for Norwegian operations in the North Sea. "We believe that will be the next market for new-builds," Nygård said.
The Aker H4.3 is an eight-column unit, which will provide good motion characteristics. Input from operational experience with various H4.2 units has been incorporated into the new rig, which meets the latest industrial standards.
This new semisubmersible is also bigger than the H3 unit. It will displace 50,000 tonnes as opposed to the H3's 18,000 tonnes. Deckload typically will be 7,000 tonnes, and the deck space will be flat too - giving crane operators a total view of the rig floor, thus allowing safer crane operations. The major change has been to provide the maximum possible deck space.
"The real focus will be to make a very efficient drilling platform," Nygård said. "The topsides are designed for maximum efficiency."
Pipe-handling will be automated. The drilling derrick will have a main and auxiliary hook to maximize parallel operations, although this will not provide the full dual-operating capability that other drilling units offer. Nevertheless, Nygård said this new layout would offer an improvement in efficiency by a factor of one-and-a-half compared with a conventional derrick.
"We have tried to capture the experience from drilling personnel. We have spent time with people already using the Aker H4.2."
Below deck, attention has been focused on the superstructure. "With six to eight leg braces below sea level, you get more steel," Nygård said, "but where you want it, far down, and the forces on the infrastructure all do not go through the deck. A large part (of the forces) goes through the structure below sea level. That makes the rig easier to modify."
Aker's move is in response to growing concern about the aging international rig fleet. Norway's Petroleum Directorate (NPD) has noted this point, and a government initiative is under way to encourage cooperation on new designs. The NPD is clearly concerned about the lack of investment in new drilling units and the age of the existing Norwegian fleet, and so has begun to push for modernization. In the background is the reluctance of rig contractors to commit to costly new-build programs without a long-term contract from an operator. The Norway initiative, managed by Konkraft, an institution established to promote offshore technology investment, aims to create the commercial basis for new rig construction.
Analyst Matt Simmons, in a 2001 speech at the Scottish Offshore Achievement Awards ceremony, suggested the North Sea in particular needs a new fleet. Simmons said the region needs new rigs to drill the relatively unexplored hinterland of northwest Europe, the Barents Sea, the Arctic and Atlantic. "Two big risks face the North Sea. The first is a lack of exploration rigs, (which are) needed if the North Sea's northern and western frontiers are ever to get explored properly," Simmons said. "Track the steady growth in North Sea rigs employed for development drilling and at some point in time, absent a new generation of exploration-dedicated rigs, the entire North Sea drilling fleet could be fully engaged, working feverishly, solely to keep the production base from declining at even steeper rates."
He identified the other risk as the number of discovered fields which lie "fallow," awaiting development activity to start.
Among those in Norway considering new-builds are Odfjell Drilling, Smedvig and a consortium headed by the Ugland Group. Odfjell is aiming to build two semi- submersibles using Aker's H4.2 design, while Ugland is considering a new drillship design from LMG of Bergen. But these depend on long-term drilling contracts in order to finance them. The only recent new-build contract was Frigstad Offshore's order for a semisubmersible to be built in Brazil using an HF Engineering design for ultradeep water, and the concept is being marketed for the US Gulf of Mexico and West Africa.
Aker's H3 adaptability
While new-builds are being considered around the world, Fred. Olsen Energy (FOE) is adapting some of its Aker H3 rigs to make them more competitive for deepwater operations.
FOE's acquisition of the new-build deepwater drillship Navis Explorer 1 in 2000 was a significant move toward realizing a declared ambition to grow in the deepwater market. The drillship is operating offshore Brazil, drilling its fourth well for Petrobras with further work for BP waiting in Trinidad.
After its recent purchase of Rig 82, FOE operates nine Aker H3 semisubmersible units, thus controlling one-third of the Aker H3 fleet.
Aker H3 rigs are designed and built for operations in harsh environments, particularly in the North Sea. They originally were certified for water depths to 1,500 ft (500 m). But the design has proven to be very versatile, and FOE believes its Aker H3 units offer cost-effective opportunities in production drilling and production modes in deepwater developments. Specifically, the company is investing in Aker H3 upgrades for slender well drilling capability in 4,920-ft to 5,576-ft (1,500-m to 1,700-m) waters, and the company has developed an Aker H3-based dry tree production unit for the same depth.
Slender well capability
Compared to standard-sized riser of 20 in. to 22 in., slender well designs are based on the use of a smaller-sized drilling riser (16-in. outer diameter), resulting in a significant reduction in riser weight, mud volumes, deck loads and riser tensioning requirements. When drilling to shallow reservoirs, the production tubing may still be standard-sized (5 1/2 in. or 7 in.). This concept allows the drilling to be carried out on the smaller and low-cost Aker H3 unit instead of big, expensive drilling rigs normally used for deepwater drilling.
Petrobras pioneered the slender well concept, demonstrating significant reductions in drilling time and costs. Other international operators are looking into using this technology for deepwater reservoirs in West Africa, the Mediterranean and the Gulf of Mexico.
Earlier this year, FOE entered a contract with ABB Offshore Systems Inc. in Houston, Texas, to upgrade one of its Aker H3 drilling rigs for slender well drilling in 5,578-ft (1,700-m) waters. The fabrication of the new modular deepwater blowout preventer (BOP) control system and a new smaller drilling riser (16 in.) is under way, and the slender well rig is being marketed for deepwater drilling operations. The focus is to reduce drilling costs without compromising safety or operational practices.
Dry completion and production
A decision to develop a deepwater field using dry production wellheads as opposed to subsea production wellheads is based on a resolution of several conflicting factors and parameters. With a view to present and future field developments, particularly in West Africa, FOE has designed a dry completion unit (DCU) based on its Aker H3 semisubmersibles. Competing dry tree concepts normally are much more
expensive purpose-built spars and tension-leg platforms.
The Aker H3 rig, with a 5,250-ft (1,600-m) water depth capacity, has the capability to carry up to 16 dry production wellheads. Production riser tensioning is based on a combination of a tensioning system on the rig and buoyancy elements on the risers below the wave-affected zone. To accommodate West African environmental conditions, a riser compensation system consisting of a set of four hydraulic
tensioners per riser with up to 33-ft (10-m) stroke is provided.
A traditional drilling module with subsea BOP and slender marine drilling riser provides full drilling capability. The derrick is skidable alongside the wells, and each individual well may be brought into
the center of the moonpool. Mooring may be by a prelaid system.
The production equipment on a 16-well deepwater DCU is limited to production and test manifold, test separator and relief systems. Further processing of the well fluid will have to take place on a floating production, storage and offloading vessel (FPSO), moored about a mile (2 km) from the DCU, that will also provide storage. In shallower water or with fewer production risers, the DCU may have additional process capacity.
The FOE concept for an Aker H3 semisubmersible as a DCU is based on existing and proven technology and offers a flexible and fast-track development solution.
Through its floating production division, Fred. Olsen Production, FOE has for
several years provided floating storage and offloading vessels and FPSOs in West
Africa. Provision and operation of the new DCU concept and the FPSO are
offered by FOE under similar lease and operate contracts.
FOE is marketing its DCU concept for smaller and medium-sized field developments (40 million bbl to 400 million bbl) in West Africa. As a result, field-specific studies for international operators are under way. AR

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