scholarly journals Imaging an Underwater Basin and its Resonance Modes using Optical Fiber Distributed Acoustic Sensing

2021 ◽  
Author(s):  
Itzhak Lior ◽  
Diego Mercerat ◽  
Diane Rivet ◽  
Anthony Sladen ◽  
Jean-Paul Ampuero
Keyword(s):  
Wave Propagation ◽  
Ambient Noise ◽  
Wave Dispersion ◽  
Velocity Model ◽  
Acoustic Sensing ◽  
Resonance Modes ◽  
Power Spectral ◽  
Basin Edge ◽  
Ideal Tool ◽  
Distributed Acoustic Sensing

Distributed acoustic sensing is an ideal tool for ambient noise tomography owing to the dense spatial measurements and the ability to continuously record in harsh environments, such as underwater. We demonstrate the ability to image a complex underwater basin using ambient noise recorded on a fiber deployed offshore Greece. A two-dimensional shear-wave velocity model was derived by analyzing Scholte-wave dispersion. In addition, extremely detailed frequency-dependent resonance and wave propagation characteristics were revealed by computing power spectral densities (PSD) and auto-correlations (AC), respectively. These observations provide crucial information on lateral and vertical wave propagation, and were used to further constrain the velocity model. The analysis reveals significant lateral variations across the short 2.5 km long fiber segment, including basin edge effects and scattered waves. Waveform simulations further support the obtained model. Our results demonstrate the advantages of incorporating PSD and AC observations into ambient noise-based imaging.

Backward piping erosion detection in levees by fiber optic acoustic sensing

2020 ◽  
Author(s):  
Juan Pablo Aguilar-López ◽  
Andres Garcia-Ruiz ◽  
Thom Bogaard ◽  
Miguel Gonzalez-Herraez
Keyword(s):  
Ambient Noise ◽  
Fiber Optic ◽  
Geophysical Methods ◽  
Innovative Technology ◽  
Fiber Optic Cable ◽  
Acoustic Sensing ◽  
Characteristic Frequencies ◽  
Distributed Acoustic Sensing ◽  
Piping Erosion ◽  
Set Up

<p>Backward piping erosion (BEP) is considered the most dangerous failure mode for levees due to its unpredictable nature. This erosive process happens most of the time underneath the impermeable layers on which levees are commonly founded. This makes it very difficult to detect as conventional geophysical methods are either too expensive or too imprecise for real time monitoring of longitudinal soil made structures such as Dams or levees. Fiber optic based distributed acoustic sensing (DAS) is an innovative technology which allows to retrieve information from an acoustic propagating medium in a spatially dense manner by using a fiber optic cable. The present study aimed to explore the potential of DAS for early detection of BEP  under levees based on the frictional emissions of the sand grains during the erosive process. The tests were performed in the lab under controlled ambient noise conditions. The technology was tested by embedding fiber optic based microphones underneath and outside a laboratory scaled aquifer set up capable of recreating BEP. The results show that indeed the process emits certain characteristic frequencies which may be located between 1200 to 1600 Hz and and that they can easily be captured by the fiber optic cables.</p>

Dual-well 3D vertical seismic profile enabled by distributed acoustic sensing in deepwater Gulf of Mexico

2015 ◽  
Vol 3 (3) ◽  
pp. SW11-SW25 ◽  
Author(s):  
Han Wu ◽  
Wai-Fan Wong ◽  
Zhaohui Yang ◽  
Peter B. Wills ◽  
Jorge L. Lopez ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Velocity Model ◽  
Seismic Profile ◽  
Seismic Survey ◽  
Vertical Seismic Profile ◽  
Acoustic Sensing ◽  
Velocity Models ◽  
Vsp Data ◽  
Distributed Acoustic Sensing

We have acquired and processed 3D vertical seismic profile (VSP) data recorded simultaneously in two wells using distributed acoustic sensing (DAS) during the acquisition of the 2012 Mars 4D ocean-bottom seismic survey in the deepwater Gulf of Mexico. The objectives of the project were to assess the quality of DAS data recorded in fiber-optic cables from the surface to the total depth, to demonstrate the efficacy of the DAS VSP technology in a deepwater environment, to derisk the use of the technology for future water injection or production monitoring without intervention, and to exploit the velocity information that 3D VSP data provide for evaluating and updating the velocity model. We evaluated the advantages of DAS VSP to reduce costs and intrusiveness, and we determined that high-quality images can be obtained from relatively noisy raw 3D DAS VSP data, as evidenced by the well 1 image, probably the best 3D VSP image we have ever seen. Our results also revealed that the direct arrival traveltimes can be used to assess the quality of an existing velocity model and to invert for an improved velocity model. We identified issues with the DAS acquisition and the processing steps to mitigate them and to handle problems specific to DAS VSP data. We described the steps for conditioning the data before migration, reverse time migration, and postmigration processing to reduce noise artifacts. We outlined a novel first-break picking procedure that works even in the absence of a strong first arrival and a velocity diagnosis method to assess and validate velocity models and velocity updates. Finally, we determined potential applications to 4D monitoring of fluid movement around producer or injector wells, identification of active salt movements, and more accurate imaging and monitoring of complex structures around the wells.

scholarly journals Horizontally orthogonal distributed acoustic sensing array for earthquake- and ambient-noise-based multichannel analysis of surface waves

2020 ◽  
Vol 222 (3) ◽  
pp. 2147-2161
Author(s):  
Bin Luo ◽  
Whitney Trainor-Guitton ◽  
Ebru Bozdağ ◽  
Lisa LaFlame ◽  
Steve Cole ◽  
...  
Keyword(s):  
Rayleigh Wave ◽  
Surface Waves ◽  
Love Wave ◽  
Ambient Noise ◽  
Wave Dispersion ◽  
Wave Component ◽  
Multichannel Analysis ◽  
Distributed Acoustic Sensing ◽  
Love Wave Dispersion

SUMMARY A 2-D orthogonal distributed acoustic sensing (DAS) array designed for seismic experiments was buried horizontally beneath the Kafadar Commons Geophysical Laboratory on the Colorado School of Mines campus at Golden, Colorado. The DAS system using straight fibre-optic cables is a cost-efficient technology that enables dense seismic array deployment for long-term seismic monitoring, favouring both earthquake-based and ambient-noise-based surface wave analysis for subsurface characterization. In our study, the horizontally orthogonal DAS array records ambient noise data for a period of about two months from November 2018 to January 2019. During this time, the array also detected seismic signals from an ML3.6 earthquake at Glenwood Springs, Colorado, which exhibit opposite signal polarities in the orthogonal DAS section recordings. We derive the transformation matrix for DAS strain measurements in horizontally orthogonal cables to retrieve both Rayleigh and Love wave dispersion information from the single-component DAS signals using the 2-D multichannel analysis of surface waves method. In addition, ambient noise interferometry is applied to long-term DAS noise recordings. Our theoretical derivation demonstrates that Rayleigh and Love wave Green's functions are coupled in the noise cross-correlation functions (NCFs) of DAS receiver pairs. Stacking NCFs over the horizontally orthogonal DAS array can constructively recover the radial Rayleigh wave component but destructively suppress the Love wave component. The multimodal Monte Carlo inversion of the earthquake-based Rayleigh wave and Love wave dispersion measurements and the noise-based Rayleigh wave measurement reveals a 1-D layered structure that agrees qualitatively with geological surveys of the site. Our study demonstrates that although straight fibre-optic cables lack broadside sensitivity, using appropriate DAS array configuration and seismic array methods can extend the seismic acquisition ability of DAS and enable its application to a broad range of scenarios.

Interferometry of ambient noise from a trenched distributed acoustic sensing array

2015 ◽  
Author(s):  
E.R. Martin* ◽  
J. Ajo-Franklin ◽  
S. Dou ◽  
N. Lindsey ◽  
T.M. Daley ◽  
...  
Keyword(s):  
Ambient Noise ◽  
Acoustic Sensing ◽  
Distributed Acoustic Sensing

Surface-wave dispersion spectrum inversion method applied to Love and Rayleigh waves recorded by distributed acoustic sensing

Geophysics ◽  
2021 ◽  
Vol 86 (1) ◽  
pp. EN1-EN12 ◽  
Author(s):  
Zhenghong Song ◽  
Xiangfang Zeng ◽  
Clifford H. Thurber
Keyword(s):  
Surface Wave ◽  
Wave Velocity ◽  
Love Wave ◽  
Wave Dispersion ◽  
Dynamic Strain ◽  
Inversion Method ◽  
Data Sets ◽  
Surface Wave Dispersion ◽  
Acoustic Sensing ◽  
Distributed Acoustic Sensing

Recently, distributed acoustic sensing (DAS) has been applied to shallow seismic structure imaging providing dense spatial sampling at a relatively low cost. DAS on a standard straight fiber-optic cable mostly records axial dynamic strain, which makes it difficult to separate the Rayleigh and Love wavefields. As a result, the mixed Rayleigh and Love wave signals cannot be used in the conventional surface-wave dispersion inversion method. Therefore, it is often ensured that the source and the cable are in the same line and only Rayleigh wave dispersion is used, which limits the constraints on structure and model resolution. We have inverted surface-wave dispersion spectra instead of dispersion curves. This inversion method can use mixed Rayleigh and Love waves recorded when the source and receiver array are not aligned. The multiple-channel records are transformed to the frequency domain, and a slant stack method is used to construct the dispersion spectra. The genetic algorithm method is used to obtain an optimal S-wave velocity model that minimizes the difference between theoretical and observed dispersion spectra. A series of synthetic tests are conducted to validate our method. The results suggest that our method not only improves the flexibility of the acquisition system design, but the Love wave data also provide additional constraints on the structure. Our method is applied to the active source and ambient noise data sets acquired at a geothermal site and provides consistent results for different data sets and acquisition geometries. The sensitivity of the dispersion spectra to layer thickness, density, and P-wave velocity is also discussed. With our method, the amount of usable data can be increased, helping deliver better subsurface images.

A Field Test of Distributed Acoustic Sensing for Ambient Noise Recording

2015 ◽  
Author(s):  
J. Ajo-Franklin* ◽  
N. Lindsey ◽  
T.M. Daley ◽  
B. Freifeld ◽  
M. Robertson ◽  
...  
Keyword(s):  
Field Test ◽  
Ambient Noise ◽  
Acoustic Sensing ◽  
Distributed Acoustic Sensing
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