Mooring Integrity in Electrification Projects - Learning from the Floating Production Sector in Early Years of Harsh Environment Operations

There is a growing interest in electrification of offshore production assets using renewable energy devices. Typical configurations have arrays of power generating devices, located a short distance away from the platform and linked by subsea cables. To date, floating offshore wind turbines and wave energy converters have been trialed as sources of electrical power. With hulls, moorings and cables set out in close proximity, there is a unique station keeping risk profile that needs to be managed, to ensure fitness for service through the life of the field. When developing electrification schemes, there is a body of relevant research that can be accessed to help identify and control mooring risks. In the early days of North Sea floating production, the industry encountered multiple instances of accelerated mooring line degradation. The causes and mitigations were researched through joint industry projects, leading to the publication of operating guidance through OGUK, the HSE, ISO and others. This guidance, along with a series of milestone papers, offers a valuable body of learning that is available to electrification projects. In this paper, the authors survey the integrity threats and challenges affecting moorings in electrification schemes that are based around small arrays of wind turbines or wave energy converters. Through qualitative risk assessment, comparison is made to mooring integrity issues in the floating production sector. The relevance of guidance from oil and gas is reviewed. Consideration is given to the consequences of a line failure, and how in some cases these may represent intolerable risks. It is argued that a through-life integrity risk assessment is essential for successful deployments; also, that existing OGUK guidance on mooring integrity be extended, to reflect the specifics of electrification projects.