As production systems extend to water depths beyond 3,000 feet, the effects of mooring and riser become increasingly significant when predicting a Spar's response. For these water depths, the viscous damping, inertial mass, current loading and restoring effects from both the mooring and riser system should be included to accurately solve the system's motion response. For some systems, these effects can magnify the extreme response, but for Spar platforms, coupling the mooring and riser with the vessel motion typically results in a reduction in extreme motion response.The ability to predict a significant reduction in the extreme motions can directly result in a smaller and less expensive mooring and riser system and indirectly in a lighter Spar platform through a reduction in payload requirements. Given the limitations of current model basins for deepwater Spar systems, quantification of the coupling effect of the mooring and riser system with the Spar hydrodynamic response can best be done through analytical software. This paper will describe recent efforts to predict and quantify these effects.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFloating Production, Storage and Offloading (FPSO) facilities have developed over the last 40 years to become an increasingly popular solution worldwide for offshore field development. To date no FPSO has been deployed within the US Gulf of Mexico (GOM) where the dominant production facilities have been fixed structures and floating production system based on Spar, TLP, and Semi-submersible platforms. Higher oil prices and significant ultra-deepwater prospects extending farther beyond established pipeline infrastructure, make FPSOs an increasingly viable option. Operators, Contractors and new entrepreneurs worldwide want to capture that market and are committing to the FPSO solution by placing orders for speculative builds. Many of these build contracts are signed without a specific field destination or production contract in hand and are contracted with a "generic" FPSO specification. The design specification of a generic FPSO presents many challenges. Selecting a workable environmental design envelope and the type of regulatory environment the vessel should satisfy are some of the early decisions that will determine the success of the investment. This paper discusses the challenges of developing a speculative build in view of regulatory requirements worldwide and in the US GOM.