Frontier Deepwater Developments – The Impact on Riser Systems Design in Water Depths Greater than 3,000m

May 2015
N. Saglar, B. Toleman, R. Thethi

The offshore industry anticipates the need for production riser systems in ultra-deepwater fields where water depths are between 3,000m to 4,500m. The development of ultra-deepwater fields leads to many challenges on the selection of the riser concept and in some instances such applications may require extending riser technology beyond its current limits. Consequently, there is a need to understand the feasibility of riser systems in such ultra-deepwater applications and the technology gaps that exist.

In ultra-deepwater, long suspended riser lengths will significantly increase the riser weight potentially leading to challenges with offshore installation related to laying vessel capability. High external and internal pressure on the riser will lead to the need for heavy wall pipes. Thick-wall riser pipe will bring about riser design challenges in fabrication of pipes, riser pipe welding, riser hang-off system selection, long-term fatigue design, and fabrication of specialty riser joints. By looking into these challenges, it is very important to select the most appropriate riser concept for the ultra-deepwater fields and understand the current pipe manufacturing limits, enabling technology needed for such systems, and technology gaps considering the critical points mentioned above.

This paper addresses the key riser design issues considering wall thickness sizing, top tension, axial dynamics, selection of pipe material, design of key components, and installation issues. This paper evaluates feasibility of a number of production and export riser configurations for ultra-deepwater applications based on existing technology, identifies current technology limits, and determines technology gaps that exist. Methods of advancing the current capability to meet the requirements of frontier deepwater applications are also proposed in the paper.

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