Geo Imaging Solutions Inc.

San Mateo, CA, United States

Geo Imaging Solutions Inc.

San Mateo, CA, United States
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Guitton A.,Geoimaging Solutions Inc. | Diaz E.,Geo Imaging Solucoes Tecnologicas em Geociencias Ltda
Geophysical Prospecting | Year: 2012

For some acquisition geometries, the cost of Full Waveform Inversion (FWI) can be considerably reduced by inverting simultaneously encoded shots. Encoded-shot strategies have the undesirable effect of leaving crosstalk noise in the final result. For FWI, changing the coding sequence periodically mitigates this effect. Another alternative is to use preconditioning, whereby the gradient is smoothed at every iteration along predefined directions. Preconditioning steers the solution towards accurate models while attenuating crosstalk artefacts. It also increases convergence speed and robustness to noise present in the data. © 2011 European Association of Geoscientists & Engineers.


Guitton A.,Geoimaging Solutions Inc. | Ayeni G.,Stanford University | Diaz E.,Colorado School of Mines
Geophysics | Year: 2012

The waveform inversion problem is inherently ill-posed. Traditionally, regularization schemes are used to address this issue. For waveform inversion, where the model is expected to have many details reflecting the physical properties of the Earth, regularization and data fitting can work in opposite directions: the former smoothing and the latter adding details to the model. We propose constraining estimated velocity fields by reparameterizing the model. This technique, also called model-space preconditioning, is based on directional Laplacian filters: It preserves most of the details of the velocity model while smoothing the solution along known geological dips. Preconditioning also yields faster convergence at early iterations. The Laplacian filters have the property to smooth or kill local planar events according to a local dip field. By construction, these filters can be inverted and used in a preconditioned waveform inversion strategy to yield geologically meaningful models. We illustrate with 2D synthetic and field data examples how preconditioning with nonstationary directional Laplacian filters outperforms traditional waveform inversion when sparse data are inverted and when sharp velocity contrasts are present. Adding geological information with preconditioning could benefit full-waveform inversion of real data whenever irregular geometry, coherent noise and lack of low frequencies are present. © 2012 Society of Exploration Geophysicists.


Guitton A.,Geo Imaging Solutions Inc. | Claerbout J.,Stanford University
Geophysical Prospecting | Year: 2010

With the pyramid transform, 2D dip spectra can be characterized by 1D prediction-error filters (pefs) and 3D dip spectra by 2D pefs. These filters, contrary to pefs estimated in the frequency-space domain (ω, x), are frequency independent. Therefore, one pef can be used to interpolate all frequencies. Similarly, one pef can be computed from all frequencies, thus yielding robust estimation of the filter in the presence of noise. This transform takes data from the frequency-space domain (ω, x) to data in a frequency-velocity domain (ω, u=ω·x) using a simple mapping procedure that leaves locations in the pyramid domain empty. Missing data in (ω, x)-space create even more empty bins in (ω, u)-space. We propose a multi-stage least-squares approach where both unknown pefs and missing data are estimated. This approach is tested on synthetic and field data examples where aliasing and irregular spacing are present. © 2010 European Association of Geoscientists & Engineers.


Claerbout J.,Stanford University | Guitton A.,Geoimaging Solutions Inc
Geophysical Prospecting | Year: 2015

Ricker-compliant deconvolution spikes at the center lobe of the Ricker wavelet. It enables deconvolution to preserve and enhance seismogram polarities. Expressing the phase spectrum as a function of lag, it works by suppressing the phase at small lags. A by-product of this decon is a pseudo-unitary (very clean) debubble filter where bubbles are lifted off the data while onset waveforms (usually Ricker) are untouched. © 2014 European Association of Geoscientists & Engineers.


Guitton A.,Geo Imaging Solutions Inc | Claerbout J.,Stanford University
Geophysics | Year: 2015

Being disturbed by the discrepancy between the Ricker wavelet and minimum phase wavelets, we wondered if a sparseness criterion could get us deconvolved data with the event polarity being more clearly evident. Five data sets found it does. The sparseness criterion we used is a hyperbolic penalty function. It ranged from l2 at small residuals to l1 at large residuals. The main pitfall was that introducing negative filter lags introduced a null space (obviously so for Gaussian data). The null space demanded a regularization. We found a formulation in the domain of the Fourier transform of a log spectrum, in which a Ricker-style regularization appeared. Curiously, this regularization eliminated the leg jumps. A quasi-Newton solver was faster than that of our earlier work, a combination of conjugate directions with a Newton solver. © 2015 Society of Exploration Geophysicists.


Kirstetter O.H.,Repsol | Guitton A.,Geoimaging Solutions Inc.
76th European Association of Geoscientists and Engineers Conference and Exhibition 2014: Experience the Energy - Incorporating SPE EUROPEC 2014 | Year: 2014

We illustrate an example of FWI successfully applied on a regional dataset from the Santos Basin. FWI is run in a tomographic mode. The velocity field obtained after FWI updates the post-salt sediments zone. It allow us to detect the post-salt high velocity Albian unit and to better image sub-salt and intra-salt features with RTM. This case study allow us to establish a FWI workflow for real data, applicable even on dataset without the optimum parameters usually required for FWI.


Claerbout J.F.,Stanford University | Guitton A.,GeoImaging Solutions Inc.
75th European Association of Geoscientists and Engineers Conference and Exhibition 2013 Incorporating SPE EUROPEC 2013: Changing Frontiers | Year: 2013

Predictive deconvolution does not yield Ricker wavelets as source wavelets. Analytic theory here tells how to fix it. The theory is not inverse theory. It is computable in N. log(N) time. Results here confirm better seismogram polarities. Copyright © (2012) by the European Association of Geoscientists & Engineers All rights reserved.


Guitton A.,GeoImaging Solutions Inc.
SEG Technical Program Expanded Abstracts | Year: 2011

With ill-posed inverse problems such as Full-Waveform Inversion (FWI), regularization schemes are needed to constrain the solution. Whereas many regularization schemes end up smoothing the model, an undesirable effect with FWI where high-resolution maps are sought, blocky regularization doesn't: it identifies and preserves strong velocity contrasts leading to step-like functions. In addition, blocky models might be required in some geological settings. These models might be needed for imaging with wave-equation based techniques such as Reverse Time Migration (RTM). Enforcing blockiness in the model space amounts to enforcing sparseness in the derivative of the model. Sparseness can be obtained using the ℓ1 norm or Cauchy function which are related to long-tailed density functions. By using different directions for the derivatives, the model can be made blocky in more than one direction: horizontally, vertically, or both. Whereas the Cauchy function produces better blocky models, the ℓ1 norm has the advantage of being convex without any need for hyperparameter estimation. © 2011 Society of Exploration Geophysicists.


Kaelin B.,Geo Imaging Solutions Inc. | Carvajal C.,Geo Imaging Solucoes Tecnologicas em Geociencias Ltda
SEG Technical Program Expanded Abstracts | Year: 2011

Reverse time migration (RTM) has become the favorite imaging methods in areas of complex geology. However, RTM is also known for producing low frequency artifacts, where sharp velocity contrasts are present. We show that the imaging condition applied with time-shift gathers offers an excellent opportunity to remove artifacts based on properties of wave propagation. © 2011 Society of Exploration Geophysicists.


Guitton A.,Geoimaging Solutions Inc.
Geophysical Prospecting | Year: 2012

With ill-posed inverse problems such as Full-Waveform Inversion, regularization schemes are needed to constrain the solution. Whereas many regularization schemes end up smoothing the model, an undesirable effect with FWI where high-resolution maps are sought, blocky regularization does not: it identifies and preserves strong velocity contrasts leading to step-like functions. These models might be needed for imaging with wave-equation based techniques such as Reverse Time Migration or for reservoir characterization. Enforcing blockiness in the model space amounts to enforcing a sparse representation of discontinuities in the model. Sparseness can be obtained using the ℓ 1 norm or Cauchy function which are related to long-tailed probability density functions. Detecting these discontinuities with vertical and horizontal gradient operators helps constraining the model in both directions. Blocky regularization can also help recovering higher wavenumbers that the data used for inversion would allow, thus helping controlling the cost of FWI. While the Cauchy function yields blockier models, both ℓ 1 and Cauchy attenuate illumination and inversion artifacts. © 2012 European Association of Geoscientists & Engineers.

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