Distributed Acoustic Sensing (DAS) (DAS) is an emerging optical fibre sensing technology that has the potential to revolutionise pipeline monitoring. This new technology promises to significantly enhance safety and integrity monitoring of critical energy infrastructure.
What is Distributed Acoustic Sensing (DAS)?
Distributed Acoustic Sensing (DAS) (DAS) utilizes the principle of optical time domain reflectometry to listen to acoustic waves travelling along an optical fibre cable. In DAS, laser pulses are sent down the fibre and any sound waves interacting with the cable cause slight variations in the backscattered light. Sophisticated signal processing can translate these subtle variations into acoustic data along the entire length of the fibre with sampling intervals as small as one meter.
In essence, the fibre optic cable acts as a distributed array of microphones. This allows DAS to continuously monitor acoustic activity along kilometres of pipeline with very high spatial resolution. Traditional acoustic monitoring techniques require discrete sensor placement and can miss events between sensor locations. DAS overcomes this limitation by turning the entire fibre into a continuous acoustic sensor.
Applications of DAS in Pipeline Monitoring
With its unique ability to constantly listen along an entire pipeline route, DAS is ideally suited for various critical monitoring applications:
One of the primary uses of DAS is to detect pipeline leaks by continuously listening for characteristic acoustic signatures. Even small leaks produce detectable low frequency sound that DAS can pick up with very high location accuracy. This allows leaks to be found much quicker than traditional techniques.
Third Party Interference Monitoring
DAS can monitor for any acoustic activity caused by third parties working near or interacting with the pipeline. Events like excavation, drilling or even gun shots in the vicinity are easily detected. This improves safety and protects pipelines from accidental damage or interference.
Pipeline Route Survey
The high spatial resolution of Distributed Acoustic Sensing (DAS) enables comprehensive acoustic surveys of pipeline routes. Changes in environmental conditions, ground movement or unauthorized construction can be identified. This helps maintain pipeline integrity and catch issues before they become problems.
Certain flow conditions within pipelines like slugging, cavitation or gas injection can create tell-tale acoustic signatures. DAS monitoring of these signatures helps operators optimize flow conditions and pipeline operations in real-time.
Advantages over Traditional Technology
DAS provides some clear advantages over traditional vibrational technologies used for pipeline monitoring:
- It offers truly continuous monitoring capability along the entire length of a fibre cable in both directions, whereas traditional technologies rely on placement of discrete vibration sensors at intervals.
- The spatial resolution of DAS (around 1 meter) is much higher than traditional acoustic monitoring systems. This allows issues to be pinpointed accurately.
- A single installed fibre can replace many vibration sensors, lowering installation and maintenance costs significantly over long distances.
- As it passively listens using existing fibre cables, no external power is required at sensor locations. This improves reliability in remote areas.
- Acoustic data from the entire length of fibre is transmitted to a central location simultaneously without loss of resolution between sensing points.
- Additional fibre can be fusion spliced as required, allowing seamless extension of the monitoring zone without limits on length.
Future Applications of DAS
As DAS technologies continue to evolve and integrate machine learning models, their applications are expected to grow exponentially. Some emerging application areas being explored include:
- Simultaneous monitoring of multiple pipeline corridors or adjacent assets from a single fibre installation to improve situational awareness.
- Pipeline third party damage prevention by coupling DAS with distributed temperature sensing for enhanced leak/excavation detection.
- Permanent reservoir monitoring using fibres installed in injection & production wells to optimize operations through continuous downhole acoustic monitoring.
- Structural health monitoring of above-ground pipeline assets, tanks, production facilities etc. through intelligent acoustic pattern recognition.
- Underground utility mapping by burying distributed fibre grids and using DAS to listen to characteristic vibrations from other buried infrastructure like cables during excavation work nearby.
- Seismic monitoring along critical energy corridors by leveraging the continuous acoustic monitoring capabilities of DAS to augment traditional sparse nodal seismic arrays.
As the capabilities of DAS advance, it has potential to transform safety, integrity and operational management across multiple industrial sectors in the coming decade.
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