The Bayu-Undan Floatover Project was executed in joint venture with Clough Offshore, a 50/50 arrangement that was set up specifically to secure and execute the contract. The combination of Aker Marine Contractors’ technical skills in marine operations and Clough’s local market knowledge and regional presence are two of the core strengths that helped the venture land its first project. A further key benefit for future joint ventures with Clough derives from access to the subsea construction vessels Deep CI and II. These, and a fleet of Anchor Handling & Tug Support vessels and submersible barges, are owned by Aker Marine Contractors’ minority shareholder Boa. A 25-year track record in marine operations has seen Aker Marine Contractors involved in some of the world’s most impressive and challenging installations. This expertise includes installation of concrete gravity-based structures such as the Troll A Gas Platform, the largest man-made structure ever to move across the face of the earth; installation of floating production units such as the Conoco Heidrun Tension Leg Platform; installation of subsea units and mooring systems, as well as marine operations such as platform abandonment services. And a key part of its portfolio is the extensive experience in topsides mating operations, using the floatover method in inshore waters, which number over 20 projects with installation weights from 3 000 tonnes to nearly 50 000 tonnes.
Preparations for innstallation of the first deck
Moving Offshore
This floatover expertise has now been applied to the engineering and execution of installations in offshore waters. In the last two years, the company has clocked up two major successes in the international arena, both of them in South East Asia. The first project was the installation of the 6 000 tonnes topsides deck for BP’s Lan Tay Platform, offshore Vietnam, completed in June 2002. The most recent, completed in August 2003, was the double integrated deck installation for the Bayu-Undan Development, offshore East Timor. Operated by ConocoPhillips, the Bayu-Undan Field Development is located in the Timor Sea, midway between the Indonesian archipelago and Northern Australia. The development, in 250 ft (80 meters) water depth, comprises a Drilling Production & Processing Platform, Compression, Utilities & Quarters Platform, an unmanned Wellhead Platform and a Floating Storage & Offloading vessel. The DPP and CUQ decks were fabricated by Hyundai Heavy Industries in Ulsan, South Korea.
Pulling "Blue Marlin" into the jacket slot
Floatover Versus Heavy Lift
The floatover method is growing in stature as the preferred installation method for offshore decks rather than heavy lift vessels, for a number of reasons. Aker Marine Contractors president Anne Mürer, explains: “There are only a handful of offshore vessels in the world that have the capacity to carry out heavy lifts – and they are very expensive. Because the availability of such vessels is very limited, this could lead to project delays while waiting for one to come on-line. Especially when the vessel – typically based in European waters – first has to sail to the project location, which in the case of Bayu-Undan, is on the other side of the world.”So why not use a modular installation method with a smaller vessel? “The prime objective with offshore installations is to minimize the costly hook-up periods spent offshore. If you are installing a 15 000 tonnes deck on a modular basis, you are spending much longer time offshore than you would be with a single installation procedure,” Mürer said.
Suited to Tropical Conditions
The floatover method is also particularly suited to conditions found in the tropical waters of south east Asia. As Bayu-Undan project manager Thor Hevrøy explains, “The water depths are typically shallower than in the North Sea and Gulf of Mexico. The substructure design therefore tends to be of the conventional jacket type, favouring the floatover method. And the largest heavy lift vessel in the area has a maximum capacity of around 3 000 tonnes.”Based at the Clough-Aker JV offices in Perth, Western Australia, Hevrøy has been involved with Bayu-Undan since day one, initially as engineering manager and more recently as project manager. The scope of work comprised conceptual design and engineering, planning the entire operation, transportation and installation of both decks. “There are two factors that make Bayu-Undan especially unique,” he says. “First, at 11 500 and 15 000 tonnes, the decks are among the heaviest to be installed using the floatover method in offshore waters. And secondly, we used a self-propelled vessel rather than a towed barge, the conventional method for floatover installations.”
Preparations for innstallations of the second deck
Added Benefits with Self-Propelled Vessels
The idea for the self-propelled vessel came from Aker Marine Contractors’ Helge Røraas, project manager at the start of the project, now in charge of the company’s activities out of Houston. “For two decks, the installation required four journeys between Ulsan, Korea and Timor Sea. With the self-propelled vessel, we were able to complete each journey in 10 days, rather than the 20 days needed with a towed barge,” Hevrøy says. The advantages are clear: reduced transportation time and costs, along with shorter installation periods offshore and earlier handover of the facility. “The self-propelled vessel has the added bonus of manoeuvrability, a significant advantage over a barge in weather sensitive operations,” adds Hevrøy. The vessel in question was the heavy lift vessel ‘Blue Marlin’, subcontracted from Dockwise of the Netherlands. This state-of-the-art vessel features a hull strength capacity of up to 50 000 tonnes, pumped ballast capacity of 423 750 ft³/hr (12 000 m³/hr), 1 766 million ft³/hr sluiced (flooding of ballast tanks) (50 000 m³/hr sluiced) and a service speed of 12–14 knots. Both deck installations were completed with very small weather delays and without major incidents or lost time injuries.
In-Depth Technical Expertise
At the heart of Aker Marine Contractors’ expertise lies an in-depth technical understanding of the conditions prevalent during a floatover operation and their likely impact. Advanced model testing and motion studies are conducted to verify the conceptual design for the installation. This is followed by analysis of the detailed design at the company’s Oslo headquarters. The detailed planning of the operation was performed at the project office in Perth. Aker Marine Contractors’ ability to design and specify critical installation devices also plays a crucial role in ensuring successful floatovers. These devices include specialist leg and deck mating units that act as shock absorbers as the vessel is ballasted and the load transfers from the vessel deck structures onto the jacket legs. Vertical and horizontal systems are also deployed, including special fenders running the length of the vessel and hydraulic units on the vessel deck to prevent damage from wave movement.
Cost-Savings through Early Involvement
Possibly even more important – in terms of ultimate cost savings for the client – is involvement by the Aker Marine Contractors team at the earliest possible stage in the projects. Preferably during conceptual design, as Mürer emphasizes. “Early decisions on and designing for the installation method can generate considerable savings further down the line. By being involved during the conceptual and detailed design phases, our engineers can provide invaluable input before construction begins, minimizing the need for costly changes later on. Detailed planning for transportation of the topsides and the installation operation also enables hook-up and completion operations to commence earlier.”
Looking to the Future
The next project to use the floatover method will be the topsides installation for Statoil’s Kristin semisubmersible, due for completion later in 2004. The semi itself will be towed and installed at the field in 2005 after pre-installation of the mooring system and suction anchors. In 2005, Aker Marine Contractors will also carry out the towing and installation of two gravity-based structures destined for offshore Sakhalin Island, in the Russian Federation. And as part of its ongoing partnership with Clough, Aker Marine Contractors is also pursuing opportunities in subsea construction and installation, using the Boa vessels Deep CI and II. At 394–459 ft (120–140 m) in length, these state-of-the-art, dynamically positioned specialist installation vessels are designed for deep and ultra deepwater projects and will help propel Aker Marine Contractors into the next phase of its development as a global provider of subsea services to the offshore oil and gas industry.
Load-out of Drilling Process & Production Deck underway in Ulsan, South Korea
Photo courtesy of ConocoPhilliphs Australia Pty Ltd.
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