FIBER SENSING DISTRIBUTED ACOUSTIC SENSING (DAS)
ASN OPENS A NEW ERA IN SUBSEA INTELLIGENT SENSING BASED ON ADVANCED DAS TECHNOLOGY
Access to a single optical fibre in a subsea cable can provide :
– Protection of submarine cables and infrastructure
– Seismic measurements and recording of seismic events
– Monitoring of marine life and oceanographic conditions
The OptoDAS interrogator is using a unique interrogation technique providing low-noise and long-range quantitative phase measurements in single mode optical fibers.
OPTODAS
- Real-time distortion free measurements of fibre strain modulation over distances in excess of 150 km by having one-way loss budget of 28 dB
- Extremely low inherent phase noise for fibre lengths up to 70-80 km
- No practical impact from connector reflections
- Configurable gauge length with spatial sampling of 1 m
- The unit can be delivered for permanent installation in a 19″ rack or packaged as a portable unit
- A dedicated software suite provides extensive functionality and flexibility for instrument control, data management, processing and display
ASN targets applications within the oil and gas industry and the subsea telecom and power cable industry
Offshore Oil and Gas DAS Applications
In-well monitoring
Platform and subsea well monitoring
• VSP, flow, sand, valves, integrity, micro-seismic
Seabed monitoring
Pipeline leak detection
• Flexible pipes used in seabed fields
Overburden monitoring
• Low-frequency seabed surface waves
Reservoir monitoring
• PP imaging for 4D seismic
Subsea infrastructure monitoring
• Health monitoring
• Electrical fault monitoring
Applications for offshore oil and gas
Subsea Cable DAS Applications
Monitoring of integrity threats to subsea cables and associated infrastructure
• Trawl activities
• Anchoring
• Dredging activities
• Vortex induced vibration
Earthquake detection
Measurment of oceanographic conditions
Reservoir monitoring
• Ocean currents
• Seabed rock slides etc
Monitoring of marine mammal activities
Localization of electrical failures
• Partial discharge effects
Applications subsea telecom and power cables
In addition, DAS is currently being used for several terrestrial applications from safety/security to rail and road monitoring.
APPLICATIONS FOR OFFSHORE OIL AND GAS
Borehole monitoring is a mature application of DAS, now entering the offshore production fields. Optical cables are being permanently installed for distributed borehole monitoring. The cables are normally clamped to the outside of production tubing or cemented into the casing annulus.
Distributed acoustic sensing is becoming a recognized monitoring tool for VSP, flow profiling, well integrity, valve control and micro-seismic.
The OptoDAS interrogator has extremely low instrument noise making it very suitable for in-well measurements. The very high optical power budget also facilitates monitoring of subsea wells with long tie-back cables without the need for specialized or engineered in-well fibre.
Seabed monitoring is an application under development. Seabed cables are very sensitive to acoustic seabed surface modes and ground movements. A single fibre in any optical cable installed on the seabed (trenched or un-trenched) can be utilized for various distributed sensing applications with high spatial sampling.
DAS recordings on seabed cables can be utilized for overburden monitoring, pipe leakage detection, time- lapsed seismic reservoir monitoring as well as health monitoring of seabed infrastructure. These applications are currently under development based on access to optical fibres on the seabed through existing riser cable solutions. Dedicated optical fibres in umbilicals, PRM cable networks, DC/FO cables, telecom cables or separate DAS cables may be used in combination with existing cable branching solutions.
The strong benefit of the OptoDAS interrogator for these applications is the low-noise characteristics and the high-power budget capability in combination of high spatial sampling.
APPLICATION FOR SUBSEA TELECOM AND POWER CABLES
Dark fibre in subsea telecom cables can be used to protect the cables against third party activities such as trawling, anchoring and dredging. Such fibre can also be used for environmental and scientific monitoring such as earthquake and tsunami detection, various oceanographic conditions and mammal monitoring.
On-line DAS monitoring with an optical cable next to an electrical high-power cable might provide an instant localization of partial discharge effects.
The OptoDAS interrogator has an extremely long range (in excess of 150 km with low attenuation fibre) making it very suitable for these seabed measurements. The interrogator has very low frequency capability (detecting signals below 0.01 Hz) and can also be used for temperature rate measurements.
DAS is currently widely used for monitoring of onshore pipelines including leak detection, external interference and ground movement monitoring.
DAS is also an attractive solution for perimeter intrusion detection targeted at the protection of critical assets in different market segments. With the long- range capability, it also provides an effective solution for border control.
By using existing optical cable networks in urban areas, DAS can provide sensing grids for high resolution traffic monitoring (including vehicle and road condition).
Railway monitoring is also an emerging application of DAS. With an optical cable along the track, DAS can provide information about moving trains, detect third party activity and locate rocks and landslide events.
The strong benefit of the OptoDAS interrogator for most of these applications is the low-noise characteristics and the high-power budget capability.
Need more information ?
The performance of the OptoDAS unit has been verified by a complete SEAFOM testing and the key results are included in the datasheet. You can request a copy of the OptoDAS datasheet by using the form below.
