Overview of Deepwater and Ultra-Deepwater Spar Risers

For more than a decade, Spar Top Tension Risers (TTRs) and Steel Catenary Risers (SCRs) have established a good track record through technology innovations. This paper describes how Spar TTR and SCR riser configurations have evolved to meet increasing industry demands and discusses the future of these riser systems. TTRs on the first Spar, Neptune, installed in the GOM in 1996, were supported by buoyancy cans. The next several Spar risers also used buoyancy cans with various improvements and modifications to the buoyancy can system design and installation method. In 2003, BP’s Holstein Spar was the first to use hydro-pneumatic tensioners to support its TTRs. The Kikeh and Perdido Spars also used tensioners. Optimization of TTRs is continuing with new construction methods such as the use of threaded and coupled (T&C) connectors instead of weld-on threaded connectors. Spar SCRs have also received widespread acceptance for deep and ultra-deepwater oil and gas production in recent years. The SCR has the advantages of relative low cost, conceptual simplicity, ease of fabrication and offshore installation. SCR hang-off options on a Spar include porch and pull tube. The pull tube option provides the most efficient technical solution for installation, brings the SCR interface above the water, which facilitates the piping hookup, and is better suited for the Spar’s architecture and transportation method. SCRs supported from a Spar have good fatigue performance in the touchdown region due to the relatively low motions of the Spar. As exploration and production activities move into deep and ultra-deepwater, and the metocean data increases in severity, Spar risers face additional design and analysis challenges. Adoption of high strength materials and strain-based design to meet these challenges is discussed.