Rizwan Sheikh, Senior Data Analyst at BMT, has shared BMT’s attempt to answer the challenge surrounding mooring integrity monitoring.
Within the oil and gas industry, pressure is growing to reconsider mooring integrity monitoring. This is, in part, due to the prediction that use of floating production systems in the offshore oil and gas industry will grow significantly until 2017. Failure on a floating production unit could lead to vessel drifting, riser ruptures, production shutdown and hydrocarbon release. And so, mooring integrity management should be effective in order to avoid the above.
With the support of operators, contractors and vendors, a recent industry guideline regarding mooring integrity has been issued by Oil & Gas UK. This guideline reinforces how, through effective monitoring and data management, integrity management both assist with the validation of mooring design strength and fatigue analyses, and detect mooring line failure.
A clear business case for effective mooring integrity monitoring
Mooring systems perform essential field station keeping. Current design practice is to engineer mooring systems that can withstand extreme environments with single, or even multiple, line failure scenarios.
The offshore industry has experienced many unexpected mooring line failures which have, in some cases, have resulted in mooring system failure. Between 2001 and 2011, there were more than two mooring system failures on average per year. During this period, nine were multiple line failures1 and other mooring incidents resulted in riser failures and hence extended field shut down2. Based on these statistics alone, there is a clear business case for effective mooring integrity monitoring.
With mooring integrity now under a renewed emphasis in the oil and gas industry, there is more of a need for a robust and cost-effective mooring integrity monitoring solution for both new-build and existing installations.
Monitoring mooring line break detection
One challenge that has emerged from these failings is the need to monitor mooring system integrity reliably for the life of the facility, without the need for costly inspection or maintenance of subsea sensors. Most mooring line monitoring systems that have been deployed to monitor mooring line tension have themselves experienced sensors failures. Now, the industry is assessing ways of monitoring mooring line break detection as opposed to measuring mooring tension in a hope that the sensors will be more robust.
Many challenges still need to be addressed
Monitoring systems for permanently moored floating systems must be able to withstand high structural loads as well as harsh sea-states for the design life of the facility. This is achieved through robust design, proper installation and periodic maintenance and servicing once in service.
BMT’s proposed solution
To meet demand for a cost-effective and reliable means of monitoring mooring system integrity, BMT has developed a system to assimilate data from a range of topside-based sensors into a topside response learning system (RLS). This uses machine learning and cognitive science to learn responses. As a result, the RLS is able to estimate the behaviour of a floating production facility given a set of impulses. Excursion monitoring can also be used as an indirect way of monitoring the integrity of the mooring system.
1. K. Ma, A. Duggal, P. Smedley, D. L’Hostis, H. Shu. “A Historical Review on Integrity Issues of Permanent Mooring Systems.” OTC 2013-24025, 2013.
2. S. Majhi, R. D’Souza. “Application of Lessons Learned from Field Experience to Design, Installation and Maintenance of FPS Moorings.” OTC 2013-24181, 2013.
Adapted from press release by Cecilia Rehn