Freestanding risers have become an increasing familiar riser solution for deepwater field developments in West Africa and more recently Brazil. A total of 4 field developments in West Africa will utilize the freestanding riser concept by the end of 2007, with a total of 14 risers installed that includes a combination of bundled risers and single pipe or pipe in pipe arrangements. To date, the Gulf of Mexico market has focused on the use of deepwater dry tree units with direct access vertical risers, or with flowlines and steel catenary risers to tieback subsea developments to the host facility. With the industry striding into ultra deepwater, evaluating the use of FPSOs with shuttle tankers, and the increased value in tying back smaller fields to existing platforms, the riser design is a critical component that must be thoroughly evaluated to accommodate ever changing design parameters such as the consideration of extreme vessel motions, temporary riser abandonment and host facility payload limitations. This paper will describe the basic design arrangement of single line freestanding risers and address the following key considerations for challenging deepwater field developments in the GOM:
- Installation methods and contract strategies;
- Accommodation of extreme vessel motions;
- Ability to accommodate temporary abandonment (transfer from Early Production System to Full Field Development);
- Field layout considerations and positive impact on flowline design issues;
- HP/HT issues;
- Suitability for tieback to existing facilities.
In addition, a case study is presented for a HPHT single line freestanding riser tied back to a payload sensitive facility, to demonstrate the riser performance in potentially harsh Gulf of Mexico environment.
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