Distributed Acoustic Sensing (DAS), the rapidly evolving optical fiber sensor technology for permanent geophysical monitoring uses fiber optic products to allow acoustic frequency strain signals to be detected over large distances and in a harsh environment. The principle of Distributed acoustic sensing is based on changes in the intensity of light reflections caused by sound waves radiating against a single-mode fiber optic cable. These changes can be detected and used to obtain a valuable information. The last decade is marked by growth in the distributed acoustic sensing market. The growth is stimulated by drivers such as the ability of the systems to operate in harsh working environments. Furthermore, Das systems based on the fiber optic equipment are not susceptible to electromagnetic interference and resistant to corrosion in humid conditions. Another driver for the DAS market is the ability of DAS technology to provide key data which helps to optimize oil and gas operations. DAS system is so sensitive that it can detect even a low-flying drone passing overhead, vandals damaging a railway line or someone probing the ground trying to find a pipeline from which to steal oil.
Walk-away data, which can be obtained with the help of the distributed acoustic sensing system, yield images that are nearly equivalent to images from traditional borehole geophones in terms of signal to noise ratio and resolution. Distributed acoustic sensing system can be used to monitor all sorts of sensitive locations, from oil and gas pipelines to railway tracks, military bases, and international borders because such system allows underground fiber optic devices to be converted into a giant string of microphones. Nowadays DAS capabilities are in use in the oil, gas, and border protection businesses. Permanently installed fiber optic infrastructure based on fiber optic devices will enable low-cost non-intrusive geophysical monitoring. Also, it should be noted, any single-mode fiber can quickly be turned into a series of listening fiber optic devices using distributed acoustic sensing with minimal fiber work at either and of the monitored fiber section. In addition to this, distributed acoustic sensing system is capable of creating a hydraulic fracturing or “fracking” that is very effective at releasing natural gas and oil trapped in rocks. This system works by sending sharply defined pulses of laser light down the cable: high-speed signal-processing techniques are used to analyze instantly what the sound is likely to be. Various seismic sensors can be used to monitor the fracking process, from test bores drilled nearby, but it is a costly and tricky process. Also, the Distributed acoustic sensing system can be used to monitor sounds coming from below ground, in particular, those produced by the water, sand, and chemicals pumped under high pressure to fracture rock during fracking.
The DAS technique relies on a phenomenon known as Rayleigh scattering, named after 19th-century British Lord Rayleigh, who discovered it. The first DAS operation was performed by Shell in 2009. Since then, this technique has been improved and widely tested in various field situations including the VSP (Vertical Seismic Profiling), microseismic measurements, well and reservoir surveillance, hydraulic fracturing monitoring and diagnostics. In addition, Shell and other oil companies are using the DAS system to monitor their fracking. It uses fiber optic devices inserted into a wellbore to build up an acoustic picture of the fracking fluid going into the rock at multiple levels. The fracking process can be constantly adjusted so that it runs in the most efficient way by having a clearer idea of how much fluid is going where. The DAS system is the ideal solution for the detection of this fluid and its pathways.
The DAS market is expected to be worth USD 440,2 Million by 2020. The major vertical in this market is oil and gas industry, followed by infrastructure and fire detection. In oilfield services, DAS is used in evaluation, completion, and production activities, and helps in cost optimization. The geographic analysis means America’s DTS manufacturers as leaders on the market. Asia Pacific (APAC) region is expected to grow the fastest during the forecast period.
Distributed acoustic sensing systems can be retrofitted to existing installations of permanent in-well fiber optics based monitoring systems with the addition of surface equipment. New installations of DAS systems are also possible and have already been performed.
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