Beyond Watch Circle Alerts: A Case Study in Mooring Failure Detection Using GPS Position Monitoring Data for a Deepwater Spar

Abstract Safe and reliable access to offshore energy, whether it be through hydrocarbon or renewable sources, often requires floating infrastructure that is held on station by well designed, well installed and closely monitored mooring systems. The bounds of what is possible with mooring integrity monitoring technology has expanded in recent years, providing stakeholders with improved risk mitigation over the life of the floating facility. GPS-based position monitoring systems are a common feature of offshore facilities. This paper presents how position monitoring data is being leveraged to go beyond excursion-limit alerts and achieve automated mooring integrity monitoring. The case study presented in this paper is for a deep-water spar facility that recently experienced a mooring line failure. A numerical model was developed to represent the as-built condition of the facility and its mooring system. Static and modal analyses were conducted to characterise the response of the facility in both the intact and mooring line failed conditions. This characterisation was then used to tune an algorithm to detect mooring failures based on GPS position data for the facility. In-field observations of GPS position data were provided to this algorithm as test data. The outputs of the failure detection algorithm using these in-field observations are presented in this paper. In addition to the algorithm being validated against an observed mooring failure, several storms were present in the data set, to test if the algorithm would raise false positive failure alerts; none were triggered. The paper also discusses how mooring integrity monitoring can be deployed in practice as a 24/7 web-based automated system, accessible to key stakeholders both on and offshore. An outline architecture for how such a system may be connected to operational data sources is provided. Adequate consideration of data security and data integrity issues are important in the deployment of such a web-based solution and an outline of the challenges that may need to be addressed are provided. By presenting a case study on how GPS data can be successfully used to monitor mooring integrity and reliably detect mooring failures whilst avoiding false positive alerts, this paper demonstrates an approach for improved risk visibility and risk mitigation for floating facility mooring systems, at lower cost and complexity than traditional mooring monitoring techniques.