Exploratory drilling is conducted in increasingly greater water depth, with recent records in 3,000 m. New technologies for ultra-deepwater drilling demand increased performance from mooring systems, such as tight watch circle, enhanced reliability, and ease of deployment. Synthetic fiber mooring lines are essential components to help meet these demands. Because of the relative lack of industry experience with this new material, advanced studies are required to confirm the suitability of polyester-based mooring systems for ultra-deepwater drilling. This paper provides information on the performance of polyester mooring lines, and compares proposed design methodologies, such as API RP 2SM, with fully coupled nonlinear mooring analyses.
As offshore drilling is conducted in increasingly deeper waters, the need for cost effective, robust station keeping systems becomes more critical. For deepwater applications, conventional mooring may not satisfy required offset limitations, mainly because of the low lateral stiffness. Consequently, conventional moorings may give large offsets under moderate weather conditions when used in deepwater locations. Taut leg mooring systems prove advantageous for deepwater applications. Some of the merits of taut systems are:
higher stiffness compared with conventional moorings leads to smaller lateral offsets, which simplifies riser design. In addition, taut mooring systems with tighter offsets lead to considerable improvements in operability,
smaller footprint reduces clash risks with subsea and other installations in the vicinity,
although the volume required to store polyester ropes on an anchor handling vessel is large, lightweight is an added value during mobilization and installation,
fairlead tensions are moderate, therefore platform payload can be increased.
In recent years, taut leg mooring systems with synthetic fiber ropes have received considerable attention since they have proved to be the only alternative to dynamic positioning for station keeping in ultra-deepwater locations.
