<i>PP</i>/<i>PS</i>anisotropic stereotomography

Nag, Steinar; Alerini, M.; Ursin, Bjørn

doi:10.1111/j.1365-246x.2010.04501.x

Cited by 9 publications

(2 citation statements)

References 49 publications

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“…In the present study, we assess stereotomography (Billette and Lambaré 1998;Billette et al 2003;Lambaré et al 2004a;Alerini et al 2007;Lambaré 2008;Nag et al 2010) as a tool to build an initial model for full waveform inversion from long-offset data. Stereotomography is a ray-based slope tomographic method, where the velocity macro-model is estimated from locally coherent events that are characterized by their slopes and traveltimes in a pre-stack data cube.…”

Section: Introductionmentioning

confidence: 99%

Building starting models for full waveform inversion from wide‐aperture data by stereotomography

Prieux

Lambaré

Operto

et al. 2012

Geophysical Prospecting

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Building an accurate initial velocity model for full waveform inversion (FWI) is a key issue to guarantee convergence of full waveform inversion towards the global minimum of a misfit function. In this study, we assess joint refraction and reflection stereotomography as a tool to build a reliable starting model for frequency‐domain full waveform inversion from long‐offset (i.e., wide‐aperture) data. Stereotomography is a slope tomographic method that is based on the inversion of traveltimes and slopes of locally‐coherent events in a data cube. One advantage of stereotomography compared to conventional traveltime reflection tomography is the semi‐automatic picking procedure of locally‐coherent events, which is easier than the picking of continuous events, and can lead to a higher density of picks. While conventional applications of stereotomography only consider short‐offset reflected waves, we assess the benefits provided by the joint inversion of reflected and refracted arrivals. Introduction of the refracted waves allows the construction of a starting model that kinematically fits the first arrivals, a necessary requirement for full waveform inversion. In a similar way to frequency‐domain full waveform inversion, we design a multiscale approach of stereotomography, which proceeds hierarchically from the wide‐aperture to the short‐aperture components of the data, to reduce the non‐linearity of the stereotomographic inversion of long‐offset data. This workflow which combines stereotomography and full waveform inversion, is applied to synthetic and real data case studies for the Valhall oil‐field target. The synthetic results show that the joint refraction and reflection stereotomography for a 24‐km maximum offset data set provides a more reliable initial model for full waveform inversion than reflection stereotomography performed for a 4‐km maximum offset data set, in particular in low‐velocity gas layers and in the deep part of a structure below a reservoir. Application of joint stereotomography, full waveform inversion and reverse‐time migration to real data reveals that the FWI models and the reverse‐time migration images computed from the stereotomography model shares several features with FWI velocity models and migrated images computed from an anisotropic reflection‐traveltime tomography model, although stereotomography was performed in the isotropic approximation. Implementation of anisotropy in joint refraction and reflection stereotomography of long‐offset data is a key issue to further improve the accuracy of the method.

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Section: Introductionmentioning

confidence: 99%

Building starting models for full waveform inversion from wide‐aperture data by stereotomography

Prieux

Lambaré

Operto

et al. 2012

Geophysical Prospecting

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“…Our aim is now to express the remaining derivatives in terms of physically intuitive wavefront attributes like in Müller's (1999) result for the isotropic case.…”

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Wavefront attributes in anisotropic media

Vanelle

Abakumov

Gajewski

2018

Geophysical Journal International

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Surface-measured wavefront attributes are the key ingredient to multiparameter methods, which are nowadays standard tools in seismic data processing. However, most operators are restricted to application to isotropic media. Whereas application of an isotropic operator will still lead to satisfactory stack results, further processing steps that interpret isotropic stacking parameters in terms of wavefront attributes will lead to erroneous results if anisotropy is present but not accounted for. In this paper, we derive relationships between the stacking parameters and anisotropic wavefront attributes that allow us to apply the common reflection surface type operator to 3-D media with arbitrary anisotropy for the zero-offset and finiteoffset configurations including converted waves. The operator itself is expressed in terms of wavefront attributes that are measured in the acquisition surface, that is, no model assumptions are made. Numerical results confirm that the accuracy of the new anisotropic operator is of the same magnitude as that of its isotropic counterpart.

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