A parametric level-set approach for seismic full-waveform inversion

Kadu, Ajinkya; Leeuwen, Tristan van; Mulder, W.A.

doi:10.1190/segam2016-13870276.1

Cited by 17 publications

(11 citation statements)

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“…The maximum velocity value found in a radius related to the local wavelength is used as a flooding constant. This improves the robustness of the workflow by avoiding the need to create domains with artificial salt values, like single level set methods would do (Kadu et al, 2016).…”

Section: Methodsmentioning

confidence: 99%

“…Several approaches to solve the problem have been proposed. Most of them are relatively expensive and rely on either additional regularization terms (Esser et al, 2015) or explicit assumptions about the model velocity distribution (Kadu et al, 2016). Here, we attempt to locate areas in which updates are determined to correspond to cycle-skipped wavepaths and update them differently until the background model is mature enough for them to be handled.…”

Section: Th Eage Conference and Exhibition 2017mentioning

confidence: 99%

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Variance-based Salt Body Reconstruction

Ovcharenko¹,

Kazei²,

Peter³

et al. 2017

Proceedings

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SummarySeismic inversions of salt bodies are challenging when updating velocity models based on Born approximationinspired gradient methods. We propose a variance-based method for velocity model reconstruction in regions complicated by massive salt bodies. The novel idea lies in retrieving useful information from simultaneous updates corresponding to different single frequencies. Instead of the commonly used averaging of single-iteration monofrequency gradients, our algorithm iteratively reconstructs salt bodies in an outer loop based on updates from a set of multiple frequencies after a few iterations of full-waveform inversion. The variance among these updates is used to identify areas where considerable cycle-skipping occurs. In such areas, we update velocities by interpolating maximum velocities within a certain region. The result of several recursive interpolations is later used as a new starting model to improve results of conventional full-waveform inversion. An application on part of the BP 2004 model highlights the evolution of the proposed approach and demonstrates its effectiveness.Topics: Full Waveform Seismic Inversion, Seismic Imaging -Theory, Velocity and Seismic Velocity Parameter Estimation -Theory Main objectives: Introduce a computationally inexpensive semi-automated method for inverting salt bodies. New aspects covered: We consider updates from different single frequencies through several iterations instead of commonly used single-iteration single-frequency gradients averaging. We propose a computationally inexpensive way to build an initial model for full-waveform inversion from relatively high frequencies. th EAGE Conference & Exhibition 2017Paris, France, 12 -15 June 2017Introduction Seismic inversions of salt bodies are one of the major challenges in full waveform inversion (FWI). In acoustic inversions, the salt-induced challenge is primarily plagued with cycle-skipping phenomena (Bunks et al., 1995). Cycle-skipping occurs when a phase shift on the wavepath from the source to the receiver is larger than half of the dominant period of the signal, and thus, depends on both the wavepath and the wavelength of the signal. Signals corresponding to long wavepaths in which energy travels through deeper parts of the model are more prone to cycle-skipping. This guides FWI to a local minima of the objective function and prevents further model improvements, especially in deep explorations. Gradual offset increase (Brossier et al., 2009) or various misfit functions (Choi and Alkhalifah, 2015, e.g.) can help mitigate the problem in the data domain. Gradient conditioning can serve the same purpose through scattering angle-based filters (Alkhalifah, 2016;Kazei et al., 2016), image-guided inversion (Ma et al., 2012) or gradient optimization (Wu and Alkhalifah, 2016). Nowadays, in high-contrast salt regions the preferred approach is utilizing imaging along with salt flooding to obtain a reasonable velocity model for FWI. Such a flooding process requires a considerable amount of user intervention including...

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Section: Methodsmentioning

confidence: 99%

Section: Th Eage Conference and Exhibition 2017mentioning

confidence: 99%

Variance-based Salt Body Reconstruction

Ovcharenko¹,

Kazei²,

Peter³

et al. 2017

Proceedings

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“…Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/ de Hoop (2013), who used a total variation norm to invert a salt-a↵ected subsurface using FWI. Regularized inversion methods could be computationally expensive when multiple runs on a fine mesh are needed and these methods often require prior assumptions about the subsurface structure (Kadu et al, 2016).The second approach involves image or gradient manipulations with single iteration updates of FWI. Processed gradients can lead to shorter paths toward the global minimum without being trapped in the local minima (Alkhalifah, 2015b.…”

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confidence: 99%

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confidence: 99%

Variance-based model interpolation for improved full-waveform inversion in the presence of salt bodies

et al. 2018

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When present in the subsurface salt bodies impact the complexity of wave-equation-based seismic imaging techniques, such as least-squares reverse-time migration, and full-waveform inversion (FWI). Typically, the Born approximation used in every iteration of least-squaresbased inversions is incapable of handling the sharp, high-contrast boundaries of salt bodies.We develop a variance-based method for reconstruction of velocity models to resolve the imaging and inversion issues caused by salt bodies. Our main idea lies in retrieving useful information from independent updates corresponding to FWI at di↵erent frequencies. After several FWI iterations we compare the model updates by considering the variance distribution between them to identify locations most prone to cycle skipping. We interpolate velocities from the surrounding environment into these high-variance areas. This approach allows the model to gradually improve from identifying easily resolvable areas and extrapolating the model updates from those to the areas that are di cult to resolve at early FWI iterations. In numerical tests, our method demonstrates the ability to obtain convergent FWI results at higher frequencies.Downloaded 08/06/18 to 109.171.137.210. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/ de Hoop (2013), who used a total variation norm to invert a salt-a↵ected subsurface using FWI. Regularized inversion methods could be computationally expensive when multiple runs on a fine mesh are needed and these methods often require prior assumptions about the subsurface structure (Kadu et al., 2016).The second approach involves image or gradient manipulations with single iteration updates of FWI. Processed gradients can lead to shorter paths toward the global minimum without being trapped in the local minima (Alkhalifah, 2015b. Image-guided inversion (Ma et al., 2012), gradient optimization (Wu and Alkhalifah, 2016) or gradient conditioning through scattering angle-based filters (Alkhalifah, 2015a;Kazei et al., 2016) can serve the same purpose.The objective of FWI is to minimize both amplitude and phase di↵erences between observed and modeled seismic data. For successful inversion the Born approximation requires the initial velocity model to deliver mismatches in travel times less than half the period (Beydoun and Tarantola, 1988). Larger errors cause cycle-skipping artifacts on the wavepaths specific to each source-receiver pair. These artifacts in the image domain can be identified as repeated contrast velocity anomalies that, in turn, lead the inversion to convergence toward a local minimum on an objective function (Virieux and Operto, 2009).Inversion of mono-frequency data allows features to be resolved at a specific scale. The inversion results from di↵erent mono-frequencies therefore do not match exactly.When mono-frequency data are modeled, the phase of a harmonic plane wave at a given point on a wavepath depends on the frequency and travel time. Hence, at di↵erent frequencies, the phases of ...

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“…Previously, we presented a robust implementation that dynamically adapts the width of the level-set boundary to obtain faster convergence (Kadu et al, 2016). This approach implicitly avoids flattening and steepening of level-set function near boundary by adjusting the width according to an approximate level-set gradient.…”

Section: Introductionmentioning

confidence: 99%

Parametric level-set full-waveform inversion in the presence of salt bodies

Kadu

Mulder

Leeuwen

2017

SEG Technical Program Expanded Abstracts 2017

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SUMMARYFull-waveform inversion attempts to estimate a high-resolution model of the Earth by inverting all the seismic data. This procedure fails if the Earth model contains high-contrast bodies such as salt and if su ciently low frequencies are absent from the data. Salt bodies are important for hydrocarbon exploration because oil or gas reservoirs are often located on their sides or underneath. We represent the shape of the salt body with a level set, constructed from radial basis functions to keep its dimensionality low. We have shown earlier that the salt body can be completely recovered if the sediment structure is already known. In this paper, we propose a strategy to simultaneously reconstruct the sediment and the salt. The sediment is implicitly represented by a bilinear interpolation kernel with a small number of variables. An alternating minimization technique solves the resulting optimization problem. The results on a synthetic model using Gauss-Newton approximation of the Hessian shows the feasibility of the approach.

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A parametric level-set approach for seismic full-waveform inversion

Cited by 17 publications

References 17 publications

Variance-based Salt Body Reconstruction

Variance-based Salt Body Reconstruction

Variance-based model interpolation for improved full-waveform inversion in the presence of salt bodies

Parametric level-set full-waveform inversion in the presence of salt bodies

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