Full–waveform inversion using the excitation representation of the source wavefield

2018

GEOPHYSICS

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CitationOh J-W, Kalita M, Alkhalifah T (2017) 3D elastic full waveform inversion using P-wave excitation amplitude: Application to OBC field data. GEOPHYSICS: 1-87. AbstractWe propose an efficient elastic full waveform inversion (FWI) based on the P-wave excitation amplitude (maximum energy arrival) approximation in the source wavefields.Because, based on the P-wave excitation approximation (ExA), the gradient direction is approximated by the cross-correlation of source and receiver wavefields at only excitation time, it estimates the gradient direction faster than its conventional counterpart. In addition to this computational speedup, the P-wave excitation approximation automatically ignores SP and SS correlations in the approximated gradient direction. In elastic FWI for ocean bottom cable (OBC) data, the descent direction for the S-wave velocity is often degraded by undesired long-wavelength features from the SS correlation. For this reason, the P-wave excitation approach increases the convergence rate of multi-parameter FWI compared to the conventional approach. The modified 2D Marmousi model with OBC acquisition is used to verify the differences between the conventional method and ExA. Finally, the feasibility of the proposed method is demonstrated on a real OBC data from North Sea.

Section: Introductionmentioning

confidence: 99%

3D elastic full-waveform inversion using P-wave excitation amplitude: Application to ocean bottom cable field data

Kalita

2018

GEOPHYSICS

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“…For initial models, we use smoothed P-and S-wave velocities. As Kalita and Alkhalifah (2016) demonstrated, the gradient directions for P-wave velocity from the boundary saving method and ExA show quite similar features. This is because, in elastic FWI, the P-wave velocity perturbation still generates only PP waves (Tarantola, 1986).…”

Section: Automatic Mode Separation Using P-wave Examentioning

confidence: 51%

“…(2) requires both the source and adjoint wavefields to be present for the dot product operation, which is computationally cumbersome especially in large 3D problems. However, ExA mitigates those requirements using the following steps (Kalita and Alkhalifah, 2016): (I) Computation of the excitation time and amplitude, (II) modification in the adjoint source by a temporal cross-correlation process of source function, (III) evaluation of gradient direction only at the excitation time. Therefore, ExA does not require storing entire wavefields.…”

Section: P-wave Exa In Elastic Fwimentioning

confidence: 99%

“…To ameliorate the former, numerous solutions exist, including boundary saving (Raknes and Weibull, 2016) schemes, time-frequency domain approaches (Sirgue et al, 2008) and wavefield compression techniques (Boehm et al, 2016). Alternately, Kalita and Alkhalifah (2016) reduce the computational overhead by approximating the source wavefield with the excitation amplitude (the most energetic arrival) and its arrival time (excitation time) in acoustic FWI. In this abstract, we employ the excitation approach (ExA) under the elastic FWI realm to mitigate both the computational and convergence issues of large-scale 3D problems.…”

Section: Introductionmentioning

confidence: 99%

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3D elastic full-waveform inversion for OBC data using the P-wave excitation amplitude

Kalita

SEG Technical Program Expanded Abstracts 2017

2017

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SummaryWe suggest a fast and efficient 3D elastic full waveform inversion (FWI) algorithm based on the excitation amplitude (maximum energy arrival) of the P-wave in the source wavefield. It evaluates the gradient direction significantly faster than its conventional counterpart. In addition, it removes the long-wavelength artifacts from the gradient, which are often originated from SS correlation process. From these advantages, the excitation approach offers faster convergence not only for the S wave velocity, but also for the entire process of multi-parameter inversion, compared to the conventional FWI. The feasibility of the proposed method is demonstrated through the synthetic Marmousi and a real OBC data from North Sea.

Study on the full‐waveform inversion strategy for 3D elastic orthorhombic anisotropic media: application to ocean bottom cable data

Geophysical Prospecting

2019

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A B S T R A C TThe multi-parameter full waveform inversion is an essential tool to estimate subsurface anisotropic properties in a reservoir that may have complex geological behaviour requiring an elastic orthorhombic medium description. For such elastic orthorhombic media, finding a proper inversion strategy to mitigate parameter trade-off and reduce the Null space is crucial considering the large number of parameters describing the medium. We apply our recently developed strategy for orthorhombic medium inversion on synthetic and real ocean bottom cable data, and find the most efficient inversion strategy. At first, we analyse the trade-off patterns in three elastic orthorhombic parameterizations for a hockey-puck-shaped model. We, then, compare the performance of these orthorhombic parameterizations on a 3D synthetic ocean bottom cable data, which are obtained from a channel-shaped model. By interpreting the inverted models based on analytic radiation patterns of the nine elastic orthorhombic parameters in each parameterization, we observe that parameterizations, which have one P-wave velocity, one S-wave velocity and seven dimensionless parameters, can be optimal to recover subsurface isotropic properties in the early stages of inversion. Then, we show that the choice of three anisotropic parameters and their deviations along the horizontal plane helps us mitigate the complexity of the multi-parameter inversion by decoupling anisotropic features, which have vertical and horizontal symmetric axes, respectively. This decoupling of isotropic and anisotropic properties enables us to perform the multi-parameter anisotropic inversion in a multi-stage manner. In addition, for the marine acquisition, we show that the number of parameters can be reduced from 9 to 4, which makes the multi-parameter inversion more practical. Finally, we apply the elastic orthorhombic inversion to real ocean bottom cable data.