Numerical evaluation of an efficient deep-water mooring configuration designed to allow a fast identification of failure events

Abstract

This work proposes a taut-leg deep-water mooring configuration with buoys, designed specifically to allow a quick and easy visual identification of the rupture of any mooring line of the system. This addresses one of the main concerns of the offshore oil & gas industry: the significant number of events of mooring line failure that has been recently observed in actual operations in deep and ultra-deep water scenarios; field experience indicates that, in current spread-mooring systems, several weeks may pass until a failure is detected. The proposed configuration also presents the additional advantages of reducing the mooring radius and the tensions on the top of the lines. The configuration is evaluated and compared with a standard taut-leg system, considering the same base case study of a typical deep-water FPSO, and using up-to-date numerical methods implemented into an in-house fully coupled nonlinear time-domain dynamic analysis tool. The results indicated that the proposed configuration provided significant improvements in the cost and performance of the mooring system, in terms of line lengths, mooring radii, tensions and offsets; and confirmed that the buoy emerges and reaches the surface in the event of a line rupture, irrespective of the point where the line has broken. This indicates that the resulting configuration is a promising technical alternative to traditional standard taut-leg systems in deep and ultra-deep water scenarios.