Technical Paper: Subsea Sensors for Nonintrusive Monitoring of Temperature, Pressure and Asset Integrity

Society: OTC
Paper Number: 20980
Presentation Date: 2010
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The growth in deepwater field developments and the need for increased oil recovery with reduced capital expenditure are pushing the technical boundaries of subsea asset design. One of the challenges facing these new developments is monitoring the structural health of their subsea production asset in an inherently inaccessible location. This is usually done through structural modeling, and either spot monitoring campaigns using micro-electro-mechnical system (MEMS) accelerometers or through subsea conventional strain gauges. Both techniques present weaknesses: MEMS sensors usually require a lot of data processing to obtain functional strain information at a desired location. And strain gauges are complicated to install in a marine environment, many failing during pressure testing or installation. Both are also susceptible to electromagnetic fields which can bias their measurement.

This paper presents details of a new, nonintrusive integrity monitoring sensor systems recently deployed in the Gulf of Mexico and West Africa on production lines. Inherently reliable, presenting no moving parts, these sensors use optical fibers embedded within a composite frame for their measurements. Using field-proven subsea fiber-optic mapping technology, these systems have delivered high frequency unbiased, on the pipe strain measurements, from which is derived pipe bending and axial loading in addition to temperature and pressure monitoring.

By providing electromagnetic-immune, low noise, and unbiased strain measurements to structural engineers so that they can verify and improve their fatigue behavior models, the non-intrusive integrity monitoring system has proven a reliable alternative to MEMS and strain gauges. Furthermore, unlike alternative solutions, this system also monitors pressure, providing production and flow assurance data in addition to integrity data making it an ideal tool within a subsea production surveillance strategy.