Oil pipelines used to transport hydrocarbons from the wellbore to an offshore or onshore platform are subject to stringent monitoring for two main reasons: leak detection and plugging. Leaks represent both an economic loss and an environmental disaster. For onshore pipelines, it is possible to carry out this surveillance using a helicopter capable of visual inspection from the air. However, this is not enough, as a leak can occur at any time, and the speed of the operator's response is crucial to limiting economic losses and environmental impact. Thanks to distributed temperature measurement (DTS) Raman systems, it is possible to continuously monitor these installations. The product inside the pipelines is transported at high pressure. When there is a leak, the pressure drops sharply, causing a sharp drop in temperature which is detected by DTS Raman. These systems are capable of distributed temperature measurements over kilometers, with measurement steps down to the meter! The other incident that can occur in a pipeline, this time off-shore (submarine cable), is a solid plug blocking the pipe. Water at the bottom of the ocean can reach 4°C, so a defect in the insulation of the structure can lead to a local cold spot where certain chemical elements can solidify and obstruct the passage of fluid. When this happens, the costs associated with shutting down operations and having to call in a vessel to unblock the pipes are very high. That's why it's not uncommon today to find pipelines equipped with a retroactive system consisting of a Raman DTS that measures the temperature along the pipeline, linked by a servo-control system to heating cables to prevent such blockages.

Still in the field of power transmission, but this time in electrical form, very-high-voltage transmission cables (225kV to 400kV) can benefit from integrated fiber optics to measure the temperature distributed over the entire cable (see picture below). With ever-increasing energy demand, thermal monitoring of the electrical network is desirable for operators, as it enables them to maximize the electrical power transported, while avoiding localized overheating which would damage the cable and lead to costly and time-consuming maintenance operations. Here again, as in the case of pipeline monitoring, it makes little sense to place a multitude of point sensors over tens of kilometers to monitor the network infrastructure. The use of a Raman DTS is a perfect solution, bypassing the cost and complexity of installing a large number of point sensors. The optical fiber can be integrated directly into the electrical cable architecture (see figure below) at the design stage. So, when the cable is laid, the sensor is also installed!

When the operator wishes to monitor this type of infrastructure over longer distances (tens of kilometers), it is necessary to change technology and use DTS Brillouin. As with DTS Raman, Brillouin technology is capable, for pipelines for example, of detecting local temperature variations and relaying the information to the operator to avoid an accident or plant shutdown. This technology, because of the greater range it is able to cover, has a lower spatial resolution. This loss of spatial resolution is not due to the Brillouin technology itself, but to the number of points. For example, covering 5km with a spatial resolution of 1m results in 5,000 measurement points, whereas covering 50km with the same resolution naturally results in a factor of 10, i.e. 50,000 points. To optimize data processing, it's best to play with the spatial resolution of the measurement.

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