Apr. 2002 Vol. 223 No. 4  European Technology Round Up
Norway
Using composite technology offshore

Ove F. Jahnsen, Kvaerner Oilfield Products

Kvaerner and Conoco formed an alliance in 1995 to investigate developing composite products for oilfield use. Two main products resulted: composite riser joints and composite tethers. These products are now marketed and produced by a new Conoco / Kvaerner joint venture company, Deepwater Composites. Only riser joints are discussed herein.

The Deepwater Composites drilling-riser program involved designing, manufacturing, and testing four, full-diameter 22-in. composite joints under static, fatigue and impact loading conditions prior to finalizing the joint design for offshore use. The composite riser joints, developed for both production and drilling operations in deep waters, have a fiber-composite body with metal end connections made of carbon fibers and epoxy resin. The weight is less than half that of a steel riser. The production-riser program involved testing four, full-diameter 10-3/4-in. composite joints that were instrumented with fiber optics. These tests confirmed that current, state-of-the-art composites are strong enough to allow reliable design and manufacture of composite risers.

The full-scale, high-pressure composite drilling riser, developed for field demonstration, is a world first. Sponsored by EU Thermie, Norsk Hydro, Shell, Chevron, Statoil and Petrobrás, Deepwater Composites has successfully tested the riser joint during operations at the Statoil-operated Heidrun tension-leg platform in the Norwegian Sea.

The opportunity to demonstrate the composite drilling-riser application on the Heidrun TLP was important because it imposed severe loading and operational conditions coupled with strict North Sea regulatory requirements. A key requirement for the composite-riser field demonstration was that operators not need additional requirements to run the system.

Installation at Heidrun. Installation in the Heidrun TLP A-41 well in July 2001 was followed by two more wells in October and December. The composite riser joint was pressure tested before and after all runs. The drillstring composite joint has been successfully tested at three locations within the string, each replacing a 22-in. titanium joint. The composite joint was first installed at the riser-string bottom, above the taper joint. Subsequently, it was installed in the middle of the string and finally, moved to a location in the splash zone, where it was subject to the highest bending load. Based on the results – which successfully met all requirements – the joint is now in normal service at the platform.

The offshore industry will adopt new technology only if it improves profitability, enhances safety or provides some enabling capability. Lowering capital investment and reducing operating and maintenance costs improves profitability. Since cost of composite riser joints is often higher than equivalent steel riser joints, improving project profitability is only realized by improving life-cycle costs.

Composite risers can impact life-cycle economics by improving payload capacity, increasing water-depth capability, improving overall system safety and reliability, and reducing maintenance cost. They can even be an enabling technology for deepwater TLP and Spar concepts or for rig upgrades. As an example, composite drilling risers require less buoyancy and have a smaller diameter than steel, enable more riser joints to be stored, and the riser joints can fit through a smaller rotary table. Also, composite riser joints are lighter; thus, they required less tension and a smaller deck load, allowing a rig to carry extra casing.