Mooring systems utilizing polyester ropes have facilitated exploration and production of deepwater fields and represent a step-change in mooring system design. As the industry expands into deeper and deeper water, the next logical step is to determine the effectiveness of additional advancements in mooring technology. One of the possibilities to enhance mooring system performance is the utilization of advanced fiber ropes constructed from such materials as aramids, high-modulus polyethylene (HMPE) and polyethylene naphthalate (PEN). These advanced fiber ropes have axial stiffness (EA) properties up to three times an equivalent polyester rope. The effect of mooring ropes with different levels of stiffness on the overall mooring system performance are evaluated for a semi-submersible floating production system located in water depths ranging 5000 feet to 15000 feet (1524 m to 4572 m). The basis for the semi-submersible floating production system (FPS) used in this study was developed previously as part of DeepStar CTR 7404, as reported in OTC 18467. The key learning from this study is that the steel components in the mooring leg create a catenary effect between fiber rope segments, so the mooring system is not a perfectly taut line. As a result the axial stiffnesses of the rope segments are less of a factor affecting mooring system response than may be expected. The results shown in this paper are part of a study performed for the Minerals Management Service (MMS).
Renzi, D.F. and Ayers, R.R., “Evaluation of Advanced Fibers for Deepwater Synthetic Fiber Mooring Systems,” Proceedings of OTC 2011 (Paper No. OTC-22218) presentation at Offshore Technology Conference Brazil, October 4–6, 2011, Rio de Janeiro, Brazil.