The successful development and deployment of a re-usable composite shape sensing mat to provide real time load and cumulative fatigue data on deep water production risers in the Gulf of Mexico
The paper describes the development and subsequent successful deployment of a shape sensing mat using fibreoptic sensors. Riser strain histories are obtained by simple deduction from the monitored riser bend shape. The system together with integral subsea electronics has been repeatedly deployed to 6000 ft water depth on one of BP's Gulf of Mexico completion riser since June 2004 and is currently in use. Furthermore, a similar system was designed and used to monitor movements of an SCR in another BP development in GOM. The technology does not require a bonding operation thus avoiding the timely, costly and unreliable aspects of traditional strain monitoring systems. The composite structure, the geometry of the sensor layout and the functionality of this 18ft long armoured composite mat is presented.
The system is designed, and subsequently demonstrated through operational experience, to be easy to install with minimum impact on deployment operations. The ability to produce real time simple data topside to the operator is confirmed. This data is of such high accuracy and reliability to contribute to topside decision making process relating to operational limits.
The confidence in the technology resulting from the successful repeated reuse of this first system has already led to other similar monitoring operations. Such systems will allow operators to accurately assess real time damage rates and to determine remaining life of risers and other similar assets. The technology also reports real i.e. experienced load conditions leading to reliable SHM analysis and validation/calibration of predictive programs. The system is robust and has also been retrofitted subsea. Unlike the conventional approach the system can be fully pressure tested and calibrated in controlled conditions prior to despatch offshore. Its cost effective deployment will open the door to the extensive riser and pipeline strain monitoring. Furthermore, it will lead to direct cost savings through reduction of damage and increase of operational windows. Tied in with predictive programs global riser response analysis in real time will become possible.
Typical data is presented from this highly successful first ever subsea deployment of this composite fibre-optic shape and load sensing technology and the paper will conclude with a brief prediction of future potential applications.
The drive to develop deeper fields coupled with environmental, legislation and financial expediency has led to increasing requirement to monitor loads real time and load histories of deep water riser and flow line systems. The demanding challenges of deep and extended subsea operations have challenged conventional strain gauging techniques. Practical difficulties of bonding and protecting the strain gauges and then the ongoing calibration issues have restricted the development of structural health monitoring technologies. Alternative techniques based on interpretation from second order effects that can be more readily measured (e.g. accelerometers and inclinometers) have been preferred.