Full-waveform inversion in acoustic orthorhombic media and application to a North Sea data set

2019

JGR Solid Earth

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Full‐waveform inversion (FWI) optimizes the subsurface properties of geophysical Earth models in such a way that the modeled data, based on these subsurface properties, match the observed data. The anisotropic properties, whether monoclinic, orthorhombic, triclinic, or vertical transversally isotropic (VTI), of the subsurface, be it a fractured reservoir or the core‐mantle boundary, are necessary to describe the observed wave phenomena. There are no principal limitations on the complexity of the anisotropy that can be inverted using FWI. However, the question remains—what kind of anisotropic descriptions of the elastic properties of the Earth can or cannot be inverted reliably from seismic waveforms? We reveal the resolution that can be achieved through reconstructions of each elastic parameter by building vertical resolution patterns from the scattering radiation patterns of body waves. A visual analysis of these patterns indicates “trade‐offs,” that is, perturbations of parameters that have the same reflection‐based scattering patterns as other perturbations. Each trade‐off leads to an apparent ambiguity in the inversion, which must be addressed by additional assumptions, constraints, or regularizations. For orthorhombic media, we find the exact trade‐offs that exist between parameters. Our parameterization isolates the VTI parameters, and therefore, we also obtain trade‐offs for every scattering mode for VTI media. We discover that only monoclinic parameters are recoverable from the first‐order scattering of monotypic waves. We summarize the trade‐offs in tables for easy reference. This paper is intended to be useful for researchers setting up anisotropic FWI problems, and interpreting or controlling the quality of such inversions.

Section: Possible Applicationsmentioning

confidence: 99%

Scattering Radiation Pattern Atlas: What Anisotropic Elastic Properties Can Body Waves Resolve?

Kazei

2019

JGR Solid Earth

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“…Note that C11 and C55 include only velocities, but C33 and C13 additionally include the anisotropic parameters one by one. As Oh and Alkhalifah (2018) and Masmoudi and Alkhalifah (2018) showed, this hierarchical parameterization enables the sequential inversion of the subsurface model parameters starting from the isotropic assumption and moving to the complex anisotropic assumption by adding the anisotropic parameters. In addition, for a surface seismic survey, we can reduce the number of influential parameters from seven to four in the elastic TTI case.…”

Section: Model Parameterizationmentioning

confidence: 99%

Multistage elastic full-waveform inversion for tilted transverse isotropic media

Shin

Geophysical Journal International

et al. 2020

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SUMMARY Seismic anisotropy is an important physical phenomenon that significantly affects wave propagation in complex sedimentary basins. When geological structures exhibit steep dips or severe folding, the symmetry axis of the transversely isotropic (TI) representation of the region can be rotated, leading to tilted transversely isotropic (TTI) media. We seek to find the optimal full-waveform inversion (FWI) strategy to estimate both the seismic velocities and the anisotropic parameters, including the tilt angle, in the presence of elastic TTI media. We first formulate the forward and inverse problems for elastic TTI media and analyse the radiation patterns of the model parameters. Based on the analyses of the radiation patterns, we propose two similar multistage FWI strategies that add inversion parameters over three stages, beginning with the isotropic parameters (horizontal P- and vertical S-wave velocity) and moving to the anisotropic parameters; the tilt angle is directly inverted in the last stage. Since diving waves, which are useful for providing long-wavelength updates, are mainly controlled by horizontal motion in anisotropic media, it is reasonable to choose the horizontal P-wave velocity rather than the vertical P-wave velocity. Then, the anisotropic parameters are inverted mainly using the reflected waves based on the isotropic background model built in the first stage. The main difference between the two multistage FWI strategies is whether the anisotropic parameter η is inverted. Comparing the two multistage FWI strategies with the simultaneous inversion strategy for a downsized version of the synthetic BP TTI model, we confirm that the multistage FWI strategies yield better inversion results than the simultaneous inversion strategy. When we compare the two multistage FWI strategies with each other for surface seismic data, ignoring η during the FWI process (focused multistage FWI) yields better inversion results for the tilt angle than those obtained with the inversion of η because η has less influence on the FWI than the other parameters and is not recovered well, which plays a role in degrading the tilt angle. Numerical examples support our conclusions that the focused multistage FWI strategy (neglecting η) is the optimal FWI strategy for TTI media and achieves computational efficiency for surface seismic data.

“…Therefore, anisotropic data often yield poor results when the isotropic approximation is used to perform an acoustic FWI. As high-performance computing and data acquisition (like large aperture) improve, anisotropic FWI is drawing considerable attention (Cheng et al 2014;Operto et al 2015;Wu and Alkhalifah 2016;Cheng et al 2016;Guitton and Alkhalifah 2017;Masmoudi and Alkhalifah 2018;Zhang et al 2018;Djebbi and Alkhalifah 2019).…”

Section: Introductionmentioning

confidence: 99%

Multi‐parameter reflection waveform inversion for acoustic transversely isotropic media with a vertical symmetry axis

Geophysical Prospecting

2020

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We would like to thank KAUST for its support and the members of Seismic Wave Analysis Group (SWAG) for their helpful discussions. The Shaheen supercomputing Laboratory in KAUST provides the computational support. We thank Statoil ASA and the Volve license partners ExxonMobil E&P Norway AS and Bayerngas Norge AS, for the release of the Volve data. We would like to thank Dr Noalwenn Dubos-Sallee as the Associate Editor and two anonymous reviewers for their helpful suggestions