Important advances in the offshore use of composite materials jointly developed by Kværner and Conoco are scheduled for this year. On the agenda are field testing of a composite riser, and qualification of a composite tether system. These are the most notable products to emerge so far from the Composite Alliance Agreement, entered into by the two companies in 1995.
"We are close to seeing a quantum leap in this field," says Harald Wiken, vice president for R&D at Kværner Oilfield Products (KOP). "The technology we are talking about here is past the drawing board. Now, it just needs demonstration."
The CompRiser development was initiated as a joint industry project (JIP) in 1997 with the aim of qualifying composite drilling riser technology through the testing and field demonstration of a high-pressure drilling riser joint. The joint is due to be installed later this year on Statoil's Heidrun Field as part of the drilling riser. During the field test, it will be exposed to a minimum of three drilling cycles in different locations along the riser.
The main components of the CompRiser are the internal protection layer, the titanium liner for pressure integrity, the composite laminate for main structural strength, the Traplock metal-to-composite interface, the titanium end-flange and an external protection layer.
Due to the combination of different materials, extreme operating conditions, and the lack of guidelines and rules for composite materials in offshore applications, an extensive program has been carried out to qualify the riser, including burst, fatigue and impact tests. In the course of the project, valuable experience has been gained in the design and fabrication of composite materials, Kværner reports. One striking example is that optimum weight design has resulted in a weight reduction of 53% for the Heidrun joint, from 5,440 kg to 2,540 kg.
Meanwhile, a full-scale test of the advanced composite tether system is due to take place this year, following successful testing of the basic elements at the NTNU and SINTEF research institutes in 1999. A join industry project is now being established to support this work, which should see the tether system qualified for offshore use in 2001. The tether will be built at KOP's umbilical factory at Moss in Norway.
Kværner has attempted to quantify the benefits offered by composite material technology. The firm calculated that incorporating composite risers and tethers in a deepwater mini-tension-leg platform would reduce displacement by about one third in a water depth of 1,400 meters, and about half in 2,000 meters compared with the use of steel tethers and risers. The use of composites can be extended to depths of 3,000 meters and above, at which point, steel is no longer an option. The capital savings for an ultra deepwater TLP, without drilling facilities, is of the order of 20-25%.
But the composite story is just beginning, says Wiken. Work is already underway with Conoco on the application of composite materials to both the hull and topsides of deepwater installations, with a view to achieving further weight and cost savings.
