scholarly journals Quasi-single mode operated few-mode fiber for distributed acoustic sensing

2019 ◽  
Author(s):  
Islam Ashry ◽  
Yuan Mao ◽  
Tien Khee Ng ◽  
Frode Hveding ◽  
Muhammad Arsalan ◽  
...  
Keyword(s):  
Single Mode ◽  
Acoustic Sensing ◽  
Distributed Acoustic Sensing

Distributed acoustic sensing of subsea wells

2020 ◽  
Vol 39 (11) ◽  
pp. 801-807
Author(s):  
Andreas Ellmauthaler ◽  
Brian C. Seabrook ◽  
Glenn A. Wilson ◽  
John Maida ◽  
Jeff Bush ◽  
...  
Keyword(s):  
Single Mode ◽  
Field Trials ◽  
Single Mode Fiber ◽  
Optical Losses ◽  
Acoustic Sensing ◽  
Well Integrity ◽  
Sand Control ◽  
Processing Algorithms ◽  
Distributed Acoustic Sensing ◽  
Optical Circulator

Topside distributed acoustic sensing (DAS) of subsea wells requires advanced optical engineering solutions to compensate for reduced acoustic bandwidth, optical losses, and back reflections that are accumulated through umbilicals, multiple wet- and dry-mate optical connectors, splices, optical feedthrough systems, and downhole fibers. To address these issues, we introduce a novel DAS solution based on subsea fiber topology consisting of two transmission fibers from topside and an optical circulator deployed in the optical flying lead at the subsea tree. This solution limits the sensing fiber portion to the downhole fiber, located below the subsea tree, and enables dry-tree-equivalent acoustic sampling frequencies of more than 10 kHz while eliminating all back reflections from multiple subsea connectors above the tree. When combined with enhanced backscatter single-mode fiber, this gives rise to a DAS interrogation system that is capable of providing dry-tree-equivalent acoustic sensing performance over the entire length of the subsea well, regardless of the tie-back distance. It also enables the same spectral-based DAS processing algorithms developed for seismic, sand control, injector/producer profiling, and well integrity on dry-tree wells to be applied directly to subsea DAS data. The performance of this subsea DAS system has been validated through a series of laboratory and field trials. We show the results of the tests and discuss how the system is deployed within subsea infrastructure.

Precise Distributed Acoustic Sensing measurements by using seafloor optical fiber cable system for seismic monitoring

2020 ◽  
Author(s):  
Masanao Shinohara ◽  
Tomoaki Yamada ◽  
Takeshi Akuhara ◽  
KImihiro Mochizuki ◽  
Shin'ichi Sakai
Keyword(s):  
Optical Fiber ◽  
Single Mode ◽  
Gauge Length ◽  
Observation System ◽  
High Signal ◽  
Seismic Observation ◽  
Acoustic Sensing ◽  
Seafloor Observation ◽  
Optical Fiber Cable ◽  
Distributed Acoustic Sensing

<p>Distributed Acoustic Sensing (DAS) measurements which utilize an optical fiber itself as a sensor can be applied for various purposes. An observation of earthquakes using an optical fiber deployed on the seafloor with DAS technology is attractive because DAS measurements enable a dense seismic observation as a long linear array. Spatial resolution of the observation reaches a few meters. The length of the array is determined by the measurement range of the DAS interrogator deployed on the optical fiber, and a fine spatial sensor interval can be configured. DAS measurements have become increasingly accurate and the current state of technology exhibit high signal quality. Because DAS measurement is useful for earthquake observation, there were some trials for an observation of earthquakes using an optical fiber deployed on the land or the seafloor. However, There are few observations using DAS technology on seafloor until the present.</p><p>In 1996, a seafloor seismic tsunami observation system using an optical fiber cable was deployed off the coast of Sanriku by Earthquake Research Institute, the University of Tokyo. The system has three seismic stations and two tsunami-meters, and a length of the cable is approximately 115 km. The system has six spare (dark) optical fibers which are dispersion shifted single mode type, and have been incorporated for future extension of the observation system. We have started development of a seafloor seismic observation system utilizing DAS technology on the Sanriku cable observation system as a next generation of marine seismic observation system. In 2019, we performed DAS measurements using a dark fiber from Sanriku seafloor observation system three times. An interrogator was installed in the cable landing station temporarily. Data were recorded with various values of parameters, such as length of data collection (array aperture), gauge length, ping rate, acquisition offset, for evaluation of data quality and signal to noise ratios. The total recording period for three measurements was approximately three weeks. As a result, many earthquakes including micro-earthquakes were recorded. The obtained data will be used to develop data processing techniques for seismic observations utilizing DAS measurements.</p><p> </p>

Combining Distributed Acoustic Sensing and Beamforming in a Volcanic Environment on Mount Meager, British Columbia.

2021 ◽  
Author(s):  
Sara Klaasen ◽  
Patrick Paitz ◽  
Jan Dettmer ◽  
Andreas Fichtner
Keyword(s):  
British Columbia ◽  
Power Distribution ◽  
High Frequency ◽  
Low Frequency ◽  
Volcanic Tremor ◽  
Extreme Environment ◽  
Volcanic Complex ◽  
Acoustic Sensing ◽  
Distributed Acoustic Sensing ◽  
Volcanic Environment

<p>We present one of the first applications of Distributed Acoustic Sensing (DAS) in a volcanic environment. The goals are twofold: First, we want to examine the feasibility of DAS in such a remote and extreme environment, and second, we search for active volcanic signals of Mount Meager in British Columbia (Canada). </p><p>The Mount Meager massif is an active volcanic complex that is estimated to have the largest geothermal potential in Canada and caused its largest recorded landslide in 2010. We installed a 3-km long fibre-optic cable at 2000 m elevation that crosses the ridge of Mount Meager and traverses the uppermost part of a glacier, yielding continuous measurements from 19 September to 17 October 2019.</p><p>We identify ~30 low-frequency (0.01-1 Hz) and 3000 high-frequency (5-45 Hz) events. The low-frequency events are not correlated with microseismic ocean or atmospheric noise sources and volcanic tremor remains a plausible origin. The frequency-power distribution of the high-frequency events indicates a natural origin, and beamforming on these events reveals distinct event clusters, predominantly in the direction of the main peaks of the volcanic complex. Numerical examples show that we can apply conventional beamforming to the data, and that the results are improved by taking the signal-to-noise ratio of individual channels into account.</p><p>The increased data quantity of DAS can outweigh the limitations due to the lower quality of individual channels in these hazardous and remote environments. We conclude that DAS is a promising tool in this setting that warrants further development.</p>

Capturing Glacier-Wide Cryoseismicity With Distributed Acoustic Sensing

2021 ◽  
Author(s):  
Fabian Walter ◽  
Patrick Paitz ◽  
Andreas Fichtner ◽  
Pascal Edme ◽  
Wojciech Gajek ◽  
...  
Keyword(s):  
Fiber Optic ◽  
Flow Line ◽  
Ground Deformation ◽  
Sensor Coverage ◽  
Mountain Glacier ◽  
Acoustic Sensing ◽  
Alpine Glacier ◽  
Glacier Ice ◽  
Distributed Acoustic Sensing ◽  
Ice Sheet Dynamics

<p>Over the past 1-2 decades, seismological measurements have provided new and unique insights into glacier and ice sheet dynamics. At the same time, sensor coverage is typically limited in harsh glacial environments with littile or no access. Turning kilometer-long fiber optic cables placed on the Earth’s surface into thousands of seismic sensors, Distributed Acoustic Sensing (DAS) may overcome the limitation of sensor coverage in the cryosphere.</p><p>First DAS applications on the Greenland and Antarctic ice sheets and on Alpine glacier ice have highlighted the technique’s superiority. Signals of natural and man-made seismic sources can be resolved with an unrivaled level of detail. This offers glaciologists new perspectives to interpret their seismograms in terms of ice structure, basal boundary conditions and source locations. However, previous studies employed only relatively small network scales with a point-like borehole deployment or < 1 km cable aperture at the ice surface.</p><p>Here we present a DAS installation, which aims to cover the majority of an Alpine glacier catchment: For one month in summer 2020 we deployed a 9 km long fiber optic cable on Rhonegletscher, Switzerland, and gathered continuous DAS data. The cable followed the glacier’s central flow line starting in the lowest kilometer of the ablation zone and extending well into the accumulation area. Even for a relatively small mountain glacier such as Rhonegletscher, cable deployment was a considerable logistical challenge. However, initial data analysis illustrates the benefit compared to conventional cryoseismological instrumentation: DAS measurements capture ground deformation over many octaves, including typical high-frequency englacial sources (10s to 100s of Hz) related to crevasse formation and basal sliding as well as long period signals (10s to 100s of seconds) of ice deformation. Depending on the presence of a snow cover, DAS records contain strong environmental noise (wind, meltwater flow, precipitation) and thus exhibit lower signal-to-noise ratios compared to conventional on-ice seismic installations. This is nevertheless outweighed by the advantage of monitoring ground unrest and ice deformation of nearly an entire glacier. We present a first compilation of signal and noise records and discuss future directions to leverage DAS data sets in glaciological research.</p><p> </p><p> </p><p> </p>

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