The First Dry Tree Semisubmersible Drilling and Production Platform Sold

Abstract

Abstract This paper discusses the Octabuoy®, which is the first semisubmersible drilling and production platform for dry tree field developments that has been sold and is being built. Its design, which is based on proven semisubmersible technology, has been validated theoretically and by extensive model testing, features excellent motions characteristics, and has been integrated by select major and independent operators as part of their tool kits. The platform meets oil and gas industry needs:For dry tree field developments in diverse environments, from benign to harsh, particularly when large topside loads carrying capacity and deepwater applications are needed.For a real alternative to other dry tree platforms in operation today.Suitability for fabrication, installation, and integration for field developments in Gulf of Mexico (GOM), North Sea, Brazil, West Africa, and Far East. The paper describes the platform's design, components, and performance characteristics. It summarizes the results of theoretical analyses and testing programs that validate its suitability for all environments including Brazilian metocean conditions. It also addresses its cost-effectiveness and flexibility regarding fabrication, installation, and integration. The platform's hull profile minimizes first order motions, parametric motions and, ultimately, fatigue problems in risers, moorings, and platform structure. Extensive model testing—including seakeeping, wind tunnel, towing, Vortex Induced Motions, and comparative tests—has validated the platform's performance. Test results have also confirmed analytical calculations, including hydrodynamic, mooring, and riser analyses. The platform features flexible topside designs and a very favorable topside-to-hull weight ratio. It accommodates conventional top-tensioned riser systems with manageable stroke ranges and steel catenary risers. It can be fabricated at shipyards worldwide using conventional shipbuilding methods and can be installed by floatover, heavy lift, or quayside. The platform can be relocated at the end of field life, thereby amortizing platform costs over multiple fields, and it can store oil in its hull. This paper summarizes the platform's value and key contribution to the oil and gas industry: It meets a need as the industry moves further offshore and into deeper waters, and it does so cost-effectively. Introduction The Octabuoy drilling and production platform is the first dry tree semisubmersible platform to be sold. One Octabuoy was sold to ATP Oil and Gas (ATP) in 2008 for deployment on ATP's Cheviot field in the UK sector of the North Sea. The Octabuoy is a deep-draft semisubmersible platform that was engineered and designed specifically to serve as a floating production unit with excellent motions performance for dry tree field developments. The Octabuoy concept evolved from three decades of semisubmersible platform experience, and it is based on proven principles and technology. Suitable for use in both benign and the harshest of environmental conditions, the Octabuoy can accommodate both production facilities and complete drilling or workover rig packages. Its design allows for flexibility of fabrication, installation, and integration methods and the possibility of relocation to multiple fields.