Polarization measurement uncertainty on three‐component VSP

Knowlton, Kelly B.; Spencer, T. W.

doi:10.1190/1.1443985

Cited by 8 publications

(8 citation statements)

References 4 publications

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“…For our approach to be valid, it is necessary that traveltimes and polarizations of direct P-waves are accurately measured from VSP data and that the separation of different arrivals is possible. In practice, the uncertainty in polarization measurement on VSP is unknown and a value of a few degrees is assumed here, in agreement with values found in the literature (de Parscau 1991;Hu & Menke 1992;Knowlton & Spencer 1996). Moreover, because in most VSP experiments the horizontal orientation of receivers is unknown, we parametrize the polarization by its incidence angle, 8, measured from the vertical axis.…”

Section: Introductionmentioning

confidence: 53%

P-wave traveltime and polarization tomography of VSP data

Bégat¹,

Farra²

1997

Geophysical Journal International

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S U M M A R YThe presence of anisotropy requires that tomographic methods be generalized to account for anisotropy. This generalization allows geological structure to be correctly imaged and allows the anisotropic parameters to be estimated. Use of isotropic inversion for imaging anisotropic structures gives systematic trends in the traveltime and polarization residuals. However, due to the limited directional coverage, the traveltimes alone may not be sufficient to study the anisotropic properties of the structure. Polarizations can provide independent information on the structure. Traveltime and polarization inversion are applied to synthetic examples simulating VSP experiments. Transverse isotropy and 1-D structure are assumed. Plots of traveltime and polarization residuals are a n important tool to detect the anomalies due to the presence of anisotropy. For receivers located in anisotropic layers, polarization residuals display consistent anomalies of several degrees. The synthetic examples show that even the simple 1-D problem is difficult, when using direct arrivals only. Large a posteriori errors in anisotropic parameters are obtained by traveltime inversion in layers where available incidence angles are less than 45". Resolution of the tomographic image of VSP data is greatly improved by a combination of traveltime and polarization information. I n order to obtain accurate inversion results, the measurement error of polarization data should be kept to within a few degrees.

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Section: Introductionmentioning

confidence: 53%

P-wave traveltime and polarization tomography of VSP data

Bégat¹,

Farra²

1997

Geophysical Journal International

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“…Minimal preprocessing was done before the inversion. For 2-D FWI, orientation of three-component VSP data into radial and vertical components is required, which is performed using polarization analysis [Knowlton and Spencer, 1996]. Since the forward problem in FWI requires a causal wavelet, the vibroseis data set is converted to minimum phase by a phase-shifting filter [Gibson and Larner, 1984].…”

Section: Preprocessingmentioning

confidence: 99%

Time‐lapse full waveform inversion of vertical seismic profile data: Workflow and application to the CO2CRC Otway project

Egorov

Pevzner

Bóna

et al. 2017

Geophysical Research Letters

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Vertical seismic profile (VSP) is one of the technologies for monitoring hydrocarbon production and CO2 geosequestration. However, quantitative interpretation of time‐lapse VSP is challenging due to its irregular distribution of source‐receiver offsets. One way to overcome this challenge is to use full waveform inversion (FWI), which does not require regular offsets. We present a workflow of elastic FWI applied to offset vertical seismic profile data for the purpose of identification and estimation of time‐lapse changes introduced by injection of 15,000 t of CO2‐rich gas mixture at 1.5 km depth. Application of this workflow to both synthetic and field data shows that elastic FWI is able to detect and quantify the time‐lapse anomaly in P wave velocity with the magnitude of 100–150 m/s.

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“…Error estimation is here obtained using a method similar to the one proposed by Knowlton & Spencer (1996) to estimate azimuth uncertainties. It consists in the perturbation of the initial time and the length of the window containing the part of waveform used to estimate rotation angles.…”

Section: Orientations Of Seismic Sensors 1245mentioning

confidence: 99%

A complex linear least-squares method to derive relative and absolute orientations of seismic sensors

Grigoli

Cesca

Dahm

et al. 2012

Geophysical Journal International

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S U M M A R YDetermining the relative orientation of the horizontal components of seismic sensors is a common problem that limits data analysis and interpretation for several acquisition setups, including linear arrays of geophones deployed in borehole installations or ocean bottom seismometers deployed at the seafloor. To solve this problem we propose a new inversion method based on a complex linear algebra approach. Relative orientation angles are retrieved by minimizing, in a least-squares sense, the l 2 -norm between the complex traces (hodograms) of adjacent pairs of sensors. This methodology can be applied without restrictions only if the wavefield recorded by each pair of sensors is very similar. In most cases, it is possible to satisfy this condition by lowpass filtering the recorded waveforms. The main advantage of our methodology is that, in the complex domain, the relative orientations of seismic sensors can be viewed as a linear inverse problem, which ensures that the preferred solution corresponds to the global minimum of a misfit function. It is also possible to use simultaneously more than one independent data set (other seismic events) to better constrain the solution of the inverse problem. Furthermore, by a computational point of view, our method results faster than the relative orientation methods based on waveform cross-correlation. After several tests on synthetic data sets we applied successfully our methodology to different types of real data. These applications include the alignment of borehole sensors relative to a Vertical Seismic Profiling (VSP) acquisition and the orientation of Ocean Bottom Seismometers (OBS) relative to a neighbouring land station of known orientation. Using land stations, the absolute orientation of OBS can be retrieved. Finally, as a last application, we checked the correct orientation for land stations of a seismological array in Germany.

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Polarization measurement uncertainty on three‐component VSP

Cited by 8 publications

References 4 publications

P-wave traveltime and polarization tomography of VSP data

P-wave traveltime and polarization tomography of VSP data

Time‐lapse full waveform inversion of vertical seismic profile data: Workflow and application to the CO2CRC Otway project

A complex linear least-squares method to derive relative and absolute orientations of seismic sensors

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