Field testing of fiber-optic distributed acoustic sensing (DAS) for subsurface seismic monitoring
TL;DR: The use of fiber-optic cable for measurement of ground motion is a relatively recent development in distributed acoustic sensing (DAS) as mentioned in this paper, with the fiber cable itself as a sensor.
Abstract: Distributed acoustic sensing (DAS) is a relatively recent development in the use of fiber-optic cable for measurement of ground motion. Discrete fiber-optic sensors, typically using a Bragg diffraction grating, have been in research and development and field testing for more than 15 years with geophysical applications at least 12 years old (Bostick, 2000, and summary in Keul et al., 2005). However, developments in recent years have sought to remove the need for point sensors by using the fiber cable itself as a sensor (Mestayer et al., 2011; Miller et al., 2012).
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TL;DR: In this paper, the authors explain how DAS works and demonstrate its usability for typical Vertical Seismic Profiling applications such as checkshots, imaging, and time-lapse monitoring.
Abstract: Distributed Acoustic Sensing is a novel technology for seismic data acquisition, particularly suitable for Vertical Seismic Profiling. It is a break-through for low-cost, on-demand, seismic monitoring of reservoirs, both onshore and offshore. In this article we explain how Distributed Acoustic Sensing works and demonstrate
its usability for typical Vertical Seismic Profiling applications such as checkshots, imaging, and time-lapse monitoring. We show numerous data examples, and discuss Distributed Acoustic Sensing as an enabler of seismic monitoring with 3D Vertical Seismic Profiling.
Key words: Borehole geophysics, Acquisition, Seismics, Time lapse, Monitoring.
314 citations
Cites result from "Field testing of fiber-optic distri..."
...For example, results from a Silixa IU are shown in Parker et al. (2012, 2013), Miller et al. (2012), Madsen et al. (2013), and Daley et al. (2013)....
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TL;DR: Lindsey et al. as discussed by the authors analyzed cataloged earthquake observations from three distributed acoustic sensing (DAS) arrays with different horizontal geometries to demonstrate some possibilities using this technology, and showed that stacking ground motion records along 20nm of fiber yield a waveform that shows a high degree of correlation in amplitude and phase with a colocated inertial seismometer record at 0.8-1.6nHz.
Abstract: Author(s): Lindsey, NJ; Martin, ER; Dreger, DS; Freifeld, B; Cole, S; James, SR; Biondi, BL; Ajo-Franklin, JB | Abstract: Our understanding of subsurface processes suffers from a profound observation bias: seismometers are sparse and clustered on continents. A new seismic recording approach, distributed acoustic sensing (DAS), transforms telecommunication fiber-optic cables into sensor arrays enabling meter-scale recording over tens of kilometers of linear fiber length. We analyze cataloged earthquake observations from three DAS arrays with different horizontal geometries to demonstrate some possibilities using this technology. In Fairbanks, Alaska, we find that stacking ground motion records along 20nm of fiber yield a waveform that shows a high degree of correlation in amplitude and phase with a colocated inertial seismometer record at 0.8–1.6nHz. Using an L-shaped DAS array in Northern California, we record the nearly vertically incident arrival of an earthquake from The Geysers Geothermal Field and estimate its backazimuth and slowness via beamforming for different phases of the seismic wavefield. Lastly, we install a fiber in existing telecommunications conduits below Stanford University and show that little cable-to-soil coupling is required for teleseismic P and S phase arrival detection.
285 citations
TL;DR: Distributed fiber-optic sensing technology coupled to existing subsea cables (dark fiber) allows observation of ocean and solid earth phenomena and highlights this method’s potential for marine geophysics.
Abstract: Distributed fiber-optic sensing technology coupled to existing subsea cables (dark fiber) allows observation of ocean and solid earth phenomena. We used an optical fiber from the cable supporting the Monterey Accelerated Research System during a 4-day maintenance period with a distributed acoustic sensing (DAS) instrument operating onshore, creating a ~10,000-component, 20-kilometer-long seismic array. Recordings of a minor earthquake wavefield identified multiple submarine fault zones. Ambient noise was dominated by shoaling ocean surface waves but also contained observations of in situ secondary microseism generation, post-low-tide bores, storm-induced sediment transport, infragravity waves, and breaking internal waves. DAS amplitudes in the microseism band tracked sea-state dynamics during a storm cycle in the northern Pacific. These observations highlight this method's potential for marine geophysics.
263 citations
TL;DR: One of the first case studies demonstrating the use of distributed acoustic sensing deployed on regional unlit fiber-optic telecommunication infrastructure (dark fiber) for broadband seismic monitoring of both near-surface soil properties and earthquake seismology is presented.
Abstract: We present one of the first case studies demonstrating the use of distributed acoustic sensing deployed on regional unlit fiber-optic telecommunication infrastructure (dark fiber) for broadband seismic monitoring of both near-surface soil properties and earthquake seismology. We recorded 7 months of passive seismic data on a 27 km section of dark fiber stretching from West Sacramento, CA to Woodland, CA, densely sampled at 2 m spacing. This dataset was processed to extract surface wave velocity information using ambient noise interferometry techniques; the resulting VS profiles were used to map both shallow structural profiles and groundwater depth, thus demonstrating that basin-scale variations in hydrological state could be resolved using this technique. The same array was utilized for detection of regional and teleseismic earthquakes and evaluated for long period response using records from the M8.1 Chiapas, Mexico 2017, Sep 8th event. The combination of these two sets of observations conclusively demonstrates that regionally extensive fiber-optic networks can effectively be utilized for a host of geoscience observation tasks at a combination of scale and resolution previously inaccessible.
257 citations
TL;DR: In this article, a modular borehole monitoring concept has been implemented to provide a suite of well-based monitoring tools that can be deployed cost effectively in a flexible and robust package.
Abstract: A modular borehole monitoring concept has been implemented to provide a suite of
well-based monitoring tools that can be deployed cost effectively in a flexible and robust
package. The initial modular borehole monitoring system was deployed as part
of a CO2 injection test operated by the Southeast Regional Carbon Sequestration
Partnership near Citronelle, Alabama. The Citronelle modular monitoring system
transmits electrical power and signals, fibre-optic light pulses, and fluids between the
surface and a reservoir. Additionally, a separate multi-conductor tubing-encapsulated
line was used for borehole geophones, including a specialized clamp for casing clamping
with tubing deployment. The deployment of geophones and fibre-optic cables allowed
comparison testing of distributed acoustic sensing. We designed a large source
effort (>64 sweeps per source point) to test fibre-optic vertical seismic profile and
acquired data in 2013. The native measurement in the specific distributed acoustic
sensing unit used (an iDAS from Silixa Ltd) is described as a localized strain rate.
Following a processing flow of adaptive noise reduction and rebalancing the signal
to dimensionless strain, improvement from repeated stacking of the source was observed.
Conversion of the rebalanced strain signal to equivalent velocity units, via
a scaling by local apparent velocity, allows quantitative comparison of distributed
acoustic sensing and geophone data in units of velocity. We see a very good match
of uncorrelated time series in both amplitude and phase, demonstrating that velocityconverted
distributed acoustic sensing data can be analyzed equivalent to vertical
geophones. We show that distributed acoustic sensing data, when averaged over an
interval comparable to typical geophone spacing, can obtain signal-to-noise ratios of
18 dB to 24 dB below clamped geophones, a result that is variable with noise spectral
amplitude because the noise characteristics are not identical. With vertical seismic profile
processing, we demonstrate the effectiveness of downgoing deconvolution from
the large spatial sampling of distributed acoustic sensing data, along with improved
upgoing reflection quality. We conclude that the extra source effort currently needed
for tubing-deployed distributed acoustic sensing vertical seismic profile, as part of a
modular monitoring system, is well compensated by the extra spatial sampling and
lower deployment cost as compared with conventional borehole geophones.
204 citations
References
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TL;DR: In this article, a multichannel shot gather is decomposed into a swept-frequency record, allowing the fast generation of an accurate dispersion curve, which can then be examined and its effects appraised in both frequency and offset space.
Abstract: The frequency-dependent properties of Rayleigh-type surface waves can be utilized for imaging and characterizing the shallow subsurface. Most surface-wave analysis relies on the accurate calculation of phase velocities for the horizontally traveling fundamental-mode Rayleigh wave acquired by stepping out a pair of receivers at intervals based on calculated ground roll wavelengths. Interference by coherent source-generated noise inhibits the reliability of shear-wave velocities determined through inversion of the whole wave field. Among these nonplanar, nonfundamental-mode Rayleigh waves (noise) are body waves, scattered and nonsource-generated surface waves, and higher-mode surface waves. The degree to which each of these types of noise contaminates the dispersion curve and, ultimately, the inverted shear-wave velocity profile is dependent on frequency as well as distance from the source. Multichannel recording permits effective identification and isolation of noise according to distinctive traceto-trace coherency in arrival time and amplitude. An added advantage is the speed and redundancy of the measurement process. Decomposition of a multichannel record into a time variable-frequency format, similar to an uncorrelated Vibroseis record, permits analysis and display of each frequency component in a unique and continuous format. Coherent noise contamination can then be examined and its effects appraised in both frequency and offset space. Separation of frequency components permits real-time maximization of the S/N ratio during acquisition and subsequent processing steps. Linear separation of each ground roll frequency component allows calculation of phase velocities by simply measuring the linear slope of each frequency component. Breaks in coherent surface-wave arrivals, observable on the decomposed record, can be compensated for during acquisition and processing. Multichannel recording permits single-measurement surveying of a broad depth range, high levels of redundancy with a single field configuration, and the ability to adjust the offset, effectively reducing random or nonlinear noise introduced during recording. A multichannel shot gather decomposed into a sweptfrequency record allows the fast generation of an accurate dispersion curve. The accuracy of dispersion curves determined using this method is proven through field comparisons of the inverted shear-wave velocity (vs) profile with a downholevs profile.
2,131 citations
"Field testing of fiber-optic distri..." refers methods in this paper
...Considering the strength of the ground roll (consisting largely of Rayleigh waves) observed in the DAS surface array, similar deployments may have utility for measuring near-surface soil properties using multichannel analysis of surface waves (MASW) techniques (Park et al., 1999)....
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TL;DR: The CO 2 SINK pilot project at Ketzin is aimed at a better understanding of geological CO 2 storage operation in a saline aquifer as discussed by the authors, which consists of fluvial deposits with average permeability ranging between 50 and 100mDarcy.
156 citations
153 citations
"Field testing of fiber-optic distri..." refers background in this paper
...However, developments in recent years have sought to remove the need for point sensors by using the fiber cable itself as a sensor (Mestayer et al., 2011; Miller et al., 2012)....
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TL;DR: The Ketzin project as mentioned in this paper is Europe's longest-operating on-shore CO2 storage site with the aim of increasing the understanding of geological storage of CO2 in saline aquifers located near Berlin.
Abstract: The Ketzin pilot site, led by the GFZ German Research Centre for Geosciences, is Europe’s longest-operating on-shore CO2 storage site with the aim of increasing the understanding of geological storage of CO2 in saline aquifers Located near Berlin, the Ketzin pilot site is an in situ laboratory for CO2 storage in an anticlinal structure in the Northeast German Basin Starting research within the framework of the EU project CO2SINK in 2004, Ketzin is Germany’s first CO2 storage site and fully in use since the injection began in June 2008 After 39 months of operation, about 53,000 tonnes of CO2 have been stored in 630–650 m deep sandstone units of the Upper Triassic Stuttgart Formation An extensive monitoring program integrates geological, geophysical and geochemical investigations at Ketzin for a comprehensive characterization of the reservoir and the CO2 migration at various scales Integrating a unique field and laboratory data set, both static geological modeling and dynamic simulations are regularly updated The Ketzin project successfully demonstrates CO2 storage in a saline aquifer on a research scale The results of monitoring and modeling can be summarized as follows: (1) Since the start of the CO2 injection in June 2008, the operation has been running reliably and safely (2) Downhole pressure data prove correlation between the injection rate and the reservoir pressure and indicates the presence of an overall dynamic equilibrium within the reservoir (3) The extensive geochemical and geophysical monitoring program is capable of detecting CO2 on different scales and gives no indication for any leakage (4) Numerical simulations (history matching) are in good agreement with the monitoring results
151 citations
"Field testing of fiber-optic distri..." refers background in this paper
...At Ketzin, Germany, a pilot CO 2 storage project was started in 2004 by the European CO2SINK group (currently operated by GFZ) at a site with multiple monitoring wells (Wuerdmann et al., 2010; Martens et al., 2012)....
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TL;DR: It is shown that the spatial distribution along the fiber of an external phase modulation can be measured with a spatial resolution close to that of optical time-domain reflectometry.
Abstract: The technique of optical time-domain reflectometry is analyzed to determine the effect of an optical phase modulation on light backscattered in an optical fiber. It is shown that the spatial distribution along the fiber of an external phase modulation can be measured with a spatial resolution close to that of optical time-domain reflectometry. A distributed interferometric sensor arrangement that employs this technique is investigated experimentally, and a satisfactory interrogation of more than 1000 resolution intervals is demonstrated.
151 citations