Deepwater Riser Technology

Abstract

Abstract The development of oil and gas reserves in water depths greater than 450 metres has seen a clear trend develop in the types of platform selected for production purposes. Floating production systems (semi-submersibles and floating production, storage and offloading facilities, FPSOs), spars and tension leg platforms (TLPs) dominate this trend. Until recently, the use of flexible marine risers has been largely unquestioned when floating structures have been employed to develop offshore oil and gas reserves. A major advantage of using a flexible riser was seen to be its compliancy with a vessel's motion. In deeper water, however, the ratio of a vessel's vertical movement to the water depth decreases. This reduces the effective strains applied to a riser due to a vessel's motion and allows alternative riser configurations to be adopted. Steel catenary risers (SCRs) and, to a lesser extent, hybrid risers are favourable configurations for use in deepwater for both production and export purposes. Flexible pipe is inherently expensive to manufacture and is restricted in the range of environments in which it can be employed (including high temperatures and for chemically aggressive product). The use of steel, and materials such as titanium, for these alternative configurations can overcome many of the disadvantages associated with flexible risers and offer promising solutions for marine risers in deeper water.