Claxton delivers world-beating riser technology to Venture Production

Claxton Engineering Services, along with Acteon group companies 2H Offshore (2H) and Subsea Riser Products (SRP), has received an order from Venture Production plc to provide an ultra-high-pressure riser for use during a high-pressure, high-temperature (HPHT) drilling campaign in the North Sea, which is scheduled for the fourth quarter of 2009.

The riser is of a very unusual design. It will be the world’s first full-bore-access (18.75 -in.) riser capable of working at pressures in excess of 12,000 PSI. Linked to this, the flanges used to connect the individual pipe sections will be attached using a shrink-fit process – another world first. As a direct result of the new riser, Venture will be able to drill and complete HPHT subsea wells from a jackup drilling rig employing a surface blowout preventer (BOP), which will provide significant cost benefits and operational efficiencies. Venture has already contracted the Noble Scott Marks, which is currently under construction in China, for the HPHT campaign.

Designing a riser of this large diameter for use at such high pressures poses considerable challenges. Engineers are forced to use either high-wall-thickness or high-strength steel, both of which are very difficult to weld, especially in cases, such as the current one, where NACE sour service requirements are cited. The proposed solution, shrink fitting the flanges to the pipes, is the key to this entire project. Shrink fitting eliminates the need for welding; high strength and fatigue-resistant connections can be made in essentially non-weldable materials.

Dannie Claxton, Technical Director, is understandably positive about the prospects of the new riser: “We have worked closely with our Acteon colleagues to offer Venture this very practical solution to the challenges of drilling high-pressure wells. The first of its type in the world, the riser is important because it gives Venture the opportunity to make a cost-effective step out in drilling practice: one we expect other companies to follow.”

As well as acting as the lead contractor, equipment integrator and offshore service supplier, Claxton Engineering Services will provide a range of ancillary equipment, including an umbilical, wellhead and BOP connectors, a tensioning ring and a hydraulic power and control system. A team from Claxton Engineering Services will be responsible for running and pulling the riser on the rig, and for its inspection and maintenance. 2H carried out the initial riser design and analysis work, and SRP led the development of the new shrink-fit technology. SRP is ultimately responsible for supplying the riser, which has 13 main sections plus fatigue-critical, tapered stress and tension joints.

Forging the main pipe sections has already commenced at two plants in France and Italy. The flanges will be forged once the main pipes are finished, and then extensive machining will be required before the flanges are shrink fitted. Once the riser is complete, a detailed testing program will be carried out before delivery to Venture in September 2009. Venture expects to begin using the riser immediately thereafter to drill HPHT development and appraisal wells in several of its Central North Sea assets in water depths to 120 m.

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