The world’s highest-pressure large-bore drilling riser

4 August 2008

04 August 2008

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

The riser is of a unique design. It will be the world’s first full-bore access (18¾-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 – the first time this technology has been used in this application.

The riser will enable Venture to drill and complete HP/HT 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 HP/HT campaign.

Alistair Montgomery, senior drilling engineer, Venture Production, said, “With HP/HT drilling on the increase across the industry, and given the tight rig market, a solution that allows us to use a jackup rig and have the full-bore access necessary to carry out subsea completions is highly significant. The contract award is the result of months of collaboration with the three Acteon companies, as well as tree supplier FMC and drilling contractor Noble Drilling. During this process safety, operational efficiency and ensuring effective systems interfaces were among our top concerns.”

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.

2H and SRP have undertaken an exhaustive development and testing programme to qualify this technology, which is likely to find broad application for both shallow and deepwater riser systems in the future. (For an explanation of this aspect of the project, see the attached technical note.)

Dannie Claxton, engineering director, Claxton Engineering, said, “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 others to follow.”

As well as acting as the lead contractor, equipment integrator and offshore service supplier, Claxton 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 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 has 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 programme will be carried out before delivery to Venture in September 2009.

Venture expects to begin using the riser immediately thereafter to drill HP/HT development and appraisal wells in several of its Central North Sea assets in water depths to 120 m.