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Keeping the flow

Published:  02 July, 2014

The recently launched Åsgard subsea compression project in the Norwegian Sea is the world’s first-ever subsea gas compression facility and a pioneering development for the industry. ODEE reports.

An issue for many subsea oil and gas fields is that decreasing natural pressure is reducing recovery and shortening the lifetime of fields. Owners of the Åsgard oilfield, situated some 200km off the coast of Norway, have developed a process that could bring benefits to the oil and gas industry for years to come.

Set for completion in 2015, the project will use subsea gas compression technology to maintain production and boost recovery from the Midgard and Mikkel reservoirs by the equivalent of about 278 million barrels of oil.

Åsgard field operator Statoil states on its website: “With Åsgard subsea gas compression, we are one step closer to realising our vision of a subsea factory. Subsea processing, and gas compression in particular, is an important technology advance to develop fields in deep waters and harsh environments.”

While this project represents a quantum leap in seabed technology, the challenging applications will increase the demands on the equipment used. Apart from being water-resistant, the equipment must withstand the temperatures and hydrostatic pressures found in deep-sea beds.

At these depths, fluids become warmer, resulting in a significant temperature difference compared with the surrounding seawater. This can cause piping wax build-up and eventually clogging, potentially leading to costly production downtime and repairs. Sophisticated thermal insulation is crucial to ensure a steady fluid flow.

With this in mind, Aker Solutions, contractor of the Åsgard subsea compression system, will apply Trelleborg’s high-performance Vikotherm R2 subsea insulation to 600m of piping. A well-proven solution, the material can easily be adapted to the varying geometries, surfaces and applications of the installation.

The rubber-based composite Vikotherm R2 system insulates and protects jumpers, manifolds, risers, pipelines, flow lines, equipment and other subsea structures. Maintenance-free, the product is designed to last the installation’s lifetime, a minimum of 30 years, so it will never normally require replacement.

“Vikotherm R2 is practically incompressible and both seawater- and impact-resistant”, says Oddvar Kopstad, sales manager Subsea at the Trelleborg Offshore & Construction facility in Norway. “It effectively withstands both low and high temperatures and provides corrosion and mechanical protection. Competing systems may have the same individual properties but are unable to offer all of them as one package.”

Vikotherm R2 is made up of three layers, all bonded to one another. The inner layer is chemically bonded to the structure surface, ensuring protection against corrosion, HISC (hydrogen-induced stress cracking) and disbondment. The middle layer provides thermal insulation, and the outer layer protects against mechanical and water ingress.

“The layer thicknesses and properties are extremely flexible,” Kopstad explains, “making it easy to adjust to environmental challenges and customer requirements.”

Launched in 2012, the Vikotherm R insulation builds on the success of its former generation, first manufactured in the late 1980s. The updated material has been subjected to years of rigorous testing, including lifetime evaluations, long-term simulated service tests and full-scale qualification tests. A notable upgrade to Vikotherm R2 is that it can be applied either on-site or at Trelleborg’s production facility in Norway. “The growing global subsea market increasingly focuses on flexibility, delivery time and quality,” says Kopstad. “So it is a huge advantage to be able to apply it on-site, anywhere in the world.”

Application at the plant involves high-pressure and high-temperature vulcanisation (typically +140°C/ +284°F) in an autoclave. Field vulcanisation is done at ambient pressure without an autoclave, but it retains the same properties.

With a market share of 20 to 25% and advanced growth plans, the future looks bright for Vikotherm R2. “In 2013, Trelleborg saw a very big increase in the specification of this solution,” Kopstad says, “and the company expects to see more growth, much of it as a direct result of Vikotherm R2’s on-site possibilities.”

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