Liuhua 11-1 FPSO & FPS Mooring System Life Extension Evaluation and Challenging Issues

Mooring system life extension for offshore floating production installation has become a hot topic for offshore industry as more and more floating units approach the end of their design lives. Some mooring system life extension projects have already been completed successfully, there are still some issues upon which the mooring industry has not reached consensus, such as field inspection capability/accuracy, uninspected items assessment, component degradation assessment, and acceptance criteria for numerical evaluation. This paper demonstrates two mooring system life extension processes located at Liuhua (LH) 11-1 oil field, following ABS rules as well as industry best practices. It also presents the challenging issues met during this long period of operation, initiated in 2016 and to be completed by end of 2019. Nanhai Shengli (NHSL) FPSO and Nanhai Tiaozhan (NHTZ) FPS are located in Liuhua 11-1 oil field. Both of the mooring systems were installed in 1995 with an originally designed life of 10 years, and already upgraded/replaced partially to extend their lives for continual safety operation. Thus, this is the second life extension for them, and some special challenges are presented. The upgrade of the mooring system is proposed based on inspection, testing, and analysis results for the existing mooring components. This paper focuses on some of the work that has been performed. These experiences may be helpful for the life extension of other similar mooring systems.