Accuracy of Distributed Optical Fiber Temperature Sensing for Use in Leak Detection of Subsea Pipelines

Accurate and rapid detection of leaks is important for subsea oil pipelines to minimize environmental risks and operational/repair costs. Temperature-sensing optical fiber cables can provide economic, near real-time sensing of leaks in subsea oil pipeline networks. By employing optical time domain reflectometry and detecting the Brillouin scattered components from a laser source, the temperature gradients can be detected at any location along an optical fiber cable attached to the oil pipeline. The feasibility of such technology has been established in the literature along with a case study on a land-based pipeline. In this paper the accuracy of an optical fiber-based temperature sensing system is investigated. A mathematical model that simulates the process of temperature sensing is developed and the results are presented. An experimental investigation is carried out with two different laboratory setups to establish the spatial resolution and accuracy of the optical fiber cable detection system, and the experimental results are compared with predictions from the theoretical model. Based on these comparisons it has been established that the optical fiber cable detection system is capable of providing an accurate and rapid assessment of the location of a leak along a subsea pipeline. Furthermore, the sensing system can be used to give an indication of the scale of the oil leak using the temperature gradients detected by the system.