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Abstract
ABSTRACTThe application of distributed acoustic sensing in borehole measurements allows for the use of fibre optic cables to measure strain. This is more efficient in terms of time and costs compared with the deploying of conventional borehole seismometers. Nevertheless, one known drawback for temporary deployment is represented by the freely hanging wireline cable slapping and ringing inside the casing, which introduces additional coherent coupling noise to the data. The present study proposes an explanation for the mechanism of noise generation and draws an analogy with similar wave propagation processes and phenomena, such as ghost waves in marine seismics. This observation allows to derive a ringing noise filter function, to study its behaviour and to consider known effects of the gauge length filter. After examining existing methods aimed at eliminating ringing noise and results of their application, we propose a two‐step approach: (1) developing a denoising method based on a matching pursuit decomposition with Gabor atoms and (2) subtracting the noise model for imaging improvement. The matching pursuit method focuses on decomposing the original input signal into a weighted sum of Gabor functions. Analysing Gabor atoms properties for frequency, amplitude and position in time provides the opportunity to distinguish parts of the original signal denoting noise caused by the vibrating cable. The matching pursuit decomposition applied to the distributed acoustic sensing‐vertical seismic profiling data at the geothermal test site Groß Schönebeck provides a versatile processing instrument for noise suppression.
Highlights
During the last decade, distributed acoustic sensing (DAS), a technology of seismic data acquisition using fibre optic cable as a linearly arranged array of sensors, has gained a wide range of application in geoscience (Dou et al, 2017; Henninges et al, 2017; Jousset et al, 2018; Mondanos and Coleman, 2019; Kobayashi et al, 2020; Naldrett et al, 2020)
We propose a physical model of so-called ringing noise and a means for its elimination based on a matching pursuit decomposition (MPD) with Gabor atoms
We briefly summarize the first two approaches here, being accompanied by the application to the Groß Schönebeck distributed acoustic sensing vertical seismic profiling (VSP) data
Summary
During the last decade, distributed acoustic sensing (DAS), a technology of seismic data acquisition using fibre optic cable as a linearly arranged array of sensors, has gained a wide range of application in geoscience (Dou et al, 2017; Henninges et al, 2017; Jousset et al, 2018; Mondanos and Coleman, 2019; Kobayashi et al, 2020; Naldrett et al, 2020). One of the possible explanations to this fact might be that the temporary cable installation causes problems with proper cable coupling and, as a result, it increases additional coherent noise in the data. Miller et al (2012) showed for the first-time data acquired using a temporarily installed fibre optic cable at Devine test site near San Antonio, Texas. For noise suppression a single-channel notch filter and orthogonal projection operators were applied
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