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The lack of low frequency components in seismic data usually leads full waveform inversion into the local minima of its objective function. An exponential damping of the data, on the other hand, generates artificial low frequencies, which can be used to admit long wavelength updates for waveform inversion. Another feature of exponential damping is that the energy of each trace also exponentially decreases with source-receiver offset, where the least-square misfit function does not work well. Thus, we propose a deconvolution-based objective function for waveform inversion with an exponential damping. Since the deconvolution filter includes a division process, it can properly address the unbalanced energy levels of the individual traces of the damped wavefield. Numerical examples demonstrate that our proposed FWI based on the deconvolution filter can generate a convergent long wavelength structure from the artificial low frequency components coming from an exponential damping.

Presentation Date: Wednesday, October 19, 2016

Start Time: 11:35:00 AM

Location: 143/149

Presentation Type: ORAL

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

Full-waveform inversion in anisotropic media using reflected waves suffers from the strong non-linearity of the objective function and trade-offs between model parameters. Estimating long-wavelength model components by fixing parameter perturbations, referred to as reflection-waveform inversion (RWI), can mitigate nonlinearity-related inversion issues. Here, we extend RWI to acoustic VTI (transversely isotropic with a vertical symmetry axis) media. To minimize trade-offs between the model parameters, we employ a new hierarchical two-stage approach that operates with the P-wave normal-moveout velocity _{nmo} and anisotropy coefficents _{nmo} is estimated using a fixed perturbation in _{nmo}. The proposed 2D algorithm is tested on a horizontally layered VTI model.

Presentation Date: Wednesday, October 19, 2016

Start Time: 8:25:00 AM

Location: 150

Presentation Type: ORAL

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

Li, Vladimir (Colorado School of Mines) | Wang, Hui (Colorado School of Mines) | Tsvankin, Ilya (Colorado School of Mines) | Diaz, Esteban (Colorado School of Mines) | Alkhalifah, Tariq (King Abdullah University of Science and Technology (KAUST))

Wavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a pseudospectral operator that employes a separable approximation of the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified stack-power objective functions. We also obtain the gradient expressions for the data-domain objective function, which can incorporate borehole information necessary for stable VTI velocity analysis. These gradients are compared to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations. Whereas the kernels computed with the two wave-equation operators are similar, the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show that the modified stack-power objective function produces cleaner gradients than the more conventional DSO operator.

Presentation Date: Wednesday, October 19, 2016

Start Time: 8:50:00 AM

Location: 150

Presentation Type: ORAL

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

Full waveform inversion (FWI) is an iterative method of data-fitting, aiming at high resolution recovery of the unknown model parameters. However, it is a cumbersome process, requiring a long computational time and large memory space/disc storage. One of the reasons for this computational limitation is the gradient calculation step. Based on the adjoint state method, it involves the temporal cross-correlation of the forward propagated source wavefield with the backward propagated residuals, in which we usually need to store the source wavefield, or include an extra extrapolation step to propagate the source wavefield from its storage at the boundary. We propose, alternatively, an amplitude excitation gradient calculation based on the excitation imaging condition concept that represents the source wavefield history by a single, specifically the most energetic arrival. An excitation based Born modeling allows us to derive the adjoint operation. In this case, the source wavelet is injected by a cross-correlation step applied to the data residual directly. Representing the source wavefield through the excitation amplitude and time, we reduce the large requirements for both storage and the computational time. We demonstrate the application of this approach on a 2-layer model with an anomaly and the Marmousi II model.

Presentation Date: Monday, October 17, 2016

Start Time: 3:45:00 PM

Location: 162/164

Presentation Type: ORAL

Alkhalifah, Tariq (King Abdullah University of Science and Technology (KAUST)) | Masmoudi, Nabil (King Abdullah University of Science and Technology (KAUST)) | Oh, Ju-Won (King Abdullah University of Science and Technology (KAUST))

Multi parameter full waveform inversion (FWI) usually suffers from the inherent tradeoff in the multi parameter nature of the model space. In orthorhombic anisotropy, such tradeoff is magnified by the large number of parameters involved in representing the elastic or even the acoustic approximation of such a medium. However, using a new parameterization with distinctive scattering features, we can condition FWI to invert for the parameters the data are sensitive to at different stages, scales, and locations in the model. Specifically, with a combination made up of a velocity and particular dimensionless ratios of the elastic coefficients, the scattering potential of the anisotropic parameters have stationary scattering radiation patterns as a function of the type of anisotropy. With our new parametrization, the data is mainly sensitive to the scattering potential of 4 parameters: the horizontal velocity in the _{1} direction, _{1} − _{3} vertical plane, _{d}_{1} and _{2} direction, and δ_{3} describing the anellipticity in the horizontal plane. Since, with this parametrization, the radiation pattern for the horizontal velocity and _{h}_{3}, and _{d}_{1}, _{d}_{3}, in the transmission to or from reflectors (especially, in the presence of large offsets). They are also sensitive to the short wavelength component of _{h}

Presentation Date: Monday, October 17, 2016

Start Time: 4:10:00 PM

Location: 166

Presentation Type: ORAL

Reflected waveform inversion (RWI) provides a method to reduce the nonlinearity of the standard full waveform inversion (FWI) by inverting for the background model using a single scattered wavefield from an inverted perturbation. However, current RWI methods are mostly based on isotropic media assumption. We extend the idea of the combining inversion for the background model and perturbations to address transversely isotropic with a vertical axis of symmetry (VTI) media taking into consideration of the optimal parameter sensitivity information. As a result, we apply Born modeling corresponding to perturbations in only for the variable

Presentation Date: Tuesday, October 18, 2016

Start Time: 1:25:00 PM

Location: 146

Presentation Type: ORAL

Oilfield Places: Oceania > Australia > Western Australia > North West Shelf > Carnarvon Basin (0.99)

The scattering angle between the source and receiver wave-fields can be utilized in full-waveform inversion (FWI) and in reverse-time migration (RTM) for regularization and quality control or to remove low frequency artifacts. The access to the scattering angle information is costly as the relation between local image features and scattering angles has non-stationary nature. For the purpose of a more efficient scattering angle information extraction, we develop techniques that utilize the simplicity of the scattering angle based filters for constant-velocity background models. We split the background velocity model into several domains with different velocity ranges, generating an "extension in velocity". We establish an analytical relation between the proposed extension and conventional RTM images extended in time and show that extending with a few samples in the newly introduced dimension is sufficient to create a scattering angle based filter. Finally the new efficient algorithm is used in a conventional FWI scheme to filter the misfit gradients and improve inversion results.

Presentation Date: Tuesday, October 18, 2016

Start Time: 10:20:00 AM

Location: 162/164

Presentation Type: ORAL

Elastic full waveform inversion (EFWI) embodies the original intention of waveform inversion at its inception as it is a better representation of the mostly solid Earth. However, compared with the acoustic P-wave assumption, EFWI for P- and S-wave velocities using multi-component data admitted mixed results. Full waveform inversion (FWI) is a highly nonlinear problem and this nonlinearity only increases under the elastic assumption. Reflection waveform inversion (RWI) can mitigate the nonlinearity by relying on transmissions from reflections focused on inverting low wavenumber components of the model. In our elastic endeavor, we split the P- and S-wave velocities into low wavenumber and perturbation components and propose a nonlinear approach to invert for both of them. The new optimization problem is built on an objective function that depends on both background and perturbation models. We utilize an equivalent stress source based on the model perturbation to generate reflection instead of demigrating from an image, which is applied in conventional RWI. Application on a slice of an ocean-bottom data shows that our method can efficiently update the low wavenumber parts of the model, but more so, obtain perturbations that can be added to the low wavenumbers for a high resolution output.

Presentation Date: Monday, October 17, 2016

Start Time: 4:35:00 PM

Location: 141

Presentation Type: ORAL

Addressing anisotropy in full wavenumber inversion (FWI) is crucial to obtaining credible models, and it is extremely challenging considering the multi parameter nature of the inversion. A successful FWI in anisotropic media takes into account the sensitivity of the data (or the wave) to the long and short wavelength components of the anisotropic parameters. Considering the low sensitivity of FWI to the anellipticity parameter

Presentation Date: Wednesday, October 19, 2016

Start Time: 2:20:00 PM

Location: 162/164

Presentation Type: ORAL

For the purpose of extracting higher resolution information from a 3D field data set, we apply a 3D elastic orthorhombic (ORT) anisotropic full waveform inversion (FWI) to hopefully better represent the physics of the Earth. We utilize what we consider as the optimal parameterization for surface acquired seismic data over a potentially orthorhombic media. This parameterization admits the possibility of incorporating a hierarchical implementation moving from higher anisotropy symmetry to lower ones. From the analysis of the radiation pattern of this new parameterization, we focus the inversion of the 3D data on the parameters that may have imprint on the data with minimal tradeoff, and as a result we invert for the horizontal P-wave velocity model, an _{1} model, its orthorhombic deviation, and the shear wave velocity. The inverted higher resolution models provide reasonable insights of the medium.

Presentation Date: Tuesday, October 18, 2016

Start Time: 3:45:00 PM

Location: 146

Presentation Type: ORAL

Oilfield Places:

- Europe > Norway > North Sea > Central North Sea > Volve Oil Field (0.99)
- Europe > Norway > North Sea > Central North Sea > Block 2/8 > Valhall Oil Field > Tor Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > Block 2/8 > Valhall Oil Field > Hod Formation (0.99)
- (2 more...)