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AuthorAlkhalifah, Tariq Ali (59)Schuster, Gerard T. (40)Hanafy, Sherif M. (8)Wang, Xin (8)Dai, Wei (7)View MoreDepartment

Physical Sciences and Engineering (PSE) Division (117)

Earth Science and Engineering Program (113)KAUST Solar Center (KSC) (4)Extreme Computing Research Center (3)Environmental Science and Engineering Program (2)View MoreJournalSEG Technical Program Expanded Abstracts 2018 (23)SEG Technical Program Expanded Abstracts 2016 (20)SEG Technical Program Expanded Abstracts 2013 (17)SEG Technical Program Expanded Abstracts 2017 (17)SEG Technical Program Expanded Abstracts 2014 (15)View MoreKAUST Grant NumberOCRF-2014-CRG3-2300 (1)Publisher
Society of Exploration Geophysicists (117)

Subjectfull-waveform inversion (27)anisotropy (19)inversion (19)migration (16)wave equation (15)View MoreType
Conference Paper (117)

Year (Issue Date)2018 (25)2017 (20)2016 (20)2015 (1)2014 (16)View MoreItem AvailabilityOpen Access (114)Metadata Only (3)

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Imaging near-surface heterogeneities by natural migration of surface waves

Liu, Zhaolun; AlTheyab, Abdullah; Hanafy, Sherif M.; Schuster, Gerard T. (SEG Technical Program Expanded Abstracts 2016, Society of Exploration Geophysicists, 2016-09-06) [Conference Paper]

We demonstrate that near-surface heterogeneities can be imaged by natural migration of backscattered surface waves in common shot gathers. No velocity model is required because the data are migrated onto surface points with the virtual Green's functions computed from the shot gathers. Migrating shot gathers recorded by 2D and 3D land surveys validates the effectiveness of detecting nearsurface heterogeneities by natural migration. The implication is that more accurate hazard maps can be created by migrating surface waves in land surveys.

Workflow for near-surface velocity automatic estimation: Source-domain full-traveltime inversion followed by waveform inversion

Liu, Lu; Fei, Tong; Luo, Yi; Guo, Bowen (SEG Technical Program Expanded Abstracts 2017, Society of Exploration Geophysicists, 2017-08-17) [Conference Paper]

This paper presents a workflow for near-surface velocity automatic estimation using the early arrivals of seismic data. This workflow comprises two methods, source-domain full traveltime inversion (FTI) and early-arrival waveform inversion. Source-domain FTI is capable of automatically generating a background velocity that can kinematically match the reconstructed plane-wave sources of early arrivals with true plane-wave sources. This method does not require picking first arrivals for inversion, which is one of the most challenging aspects of ray-based first-arrival tomographic inversion. Moreover, compared with conventional Born-based methods, source-domain FTI can distinguish between slower or faster initial model errors via providing the correct sign of the model gradient. In addition, this method does not need estimation of the source wavelet, which is a requirement for receiver-domain wave-equation velocity inversion. The model derived from source-domain FTI is then used as input to early-arrival waveform inversion to obtain the short-wavelength velocity components. We have tested the workflow on synthetic and field seismic data sets. The results show source-domain FTI can generate reasonable background velocities for early-arrival waveform inversion even when subsurface velocity reversals are present and the workflow can produce a high-resolution near-surface velocity model.

Elastic reflection waveform inversion with variable density

Li, Yuanyuan; Li, Zhenchun; Alkhalifah, Tariq Ali; Guo, Qiang (SEG Technical Program Expanded Abstracts 2017, Society of Exploration Geophysicists, 2017-08-17) [Conference Paper]

Elastic full waveform inversion (FWI) provides a better description of the subsurface than those given by the acoustic assumption. However it suffers from a more serious cycle skipping problem compared with the latter. Reflection waveform inversion (RWI) provides a method to build a good background model, which can serve as an initial model for elastic FWI. Therefore, we introduce the concept of RWI for elastic media, and propose elastic RWI with variable density. We apply Born modeling to generate the synthetic reflection data by using optimized perturbations of P- and S-wave velocities and density. The inversion for the perturbations in P- and S-wave velocities and density is similar to elastic least-squares reverse time migration (LSRTM). An incorrect initial model will lead to some misfits at the far offsets of reflections; thus, can be utilized to update the background velocity. We optimize the perturbation and background models in a nested approach. Numerical tests on the Marmousi model demonstrate that our method is able to build reasonably good background models for elastic FWI with absence of low frequencies, and it can deal with the variable density, which is needed in real cases.

Interferometric full-waveform inversion of time-lapse data

Sinha, Mrinal (SEG Technical Program Expanded Abstracts 2017, Society of Exploration Geophysicists, 2017-08-17) [Conference Paper]

One of the key challenges associated with time-lapse surveys is ensuring the repeatability between the baseline and monitor surveys. Non-repeatability between the surveys is caused by varying environmental conditions over the course of different surveys. To overcome this challenge, we propose the use of interferometric full waveform inversion (IFWI) for inverting the velocity model from data recorded by baseline and monitor surveys. A known reflector is used as the reference reflector for IFWI, and the data are naturally redatumed to this reference reflector using natural reflections as the redatuming operator. This natural redatuming mitigates the artifacts introduced by the repeatability errors that originate above the reference reflector.

Multiscale phase inversion of seismic marine data

Fu, Lei (SEG Technical Program Expanded Abstracts 2017, Society of Exploration Geophysicists, 2017-08-17) [Conference Paper]

We test the feasibility of applying multiscale phase inversion (MPI) to seismic marine data. To avoid cycle-skipping, the multiscale strategy temporally integrates the traces several times, i.e. high-order integration, to produce low-boost seismograms that are used as input data for the initial iterations of MPI. As the iterations proceed, higher frequencies in the data are boosted by using integrated traces of lower order as the input data. Results with synthetic data and field data from the Gulf of Mexico produce robust and accurate results if the model does not contain strong velocity contrasts such as salt-sediment interfaces.

Skeletonized wave-equation Qs tomography using surface waves

Li, Jing; Dutta, Gaurav; Schuster, Gerard T. (SEG Technical Program Expanded Abstracts 2017, Society of Exploration Geophysicists, 2017-08-17) [Conference Paper]

We present a skeletonized inversion method that inverts surface-wave data for the Qs quality factor. Similar to the inversion of dispersion curves for the S-wave velocity model, the complicated surface-wave arrivals are skeletonized as simpler data, namely the amplitude spectra of the windowed Rayleigh-wave arrivals. The optimal Qs model is then found that minimizes the difference in the peak frequencies of the predicted and observed Rayleigh wave arrivals using a gradient-based wave-equation optimization method. Solutions to the viscoelastic wave-equation are used to compute the predicted Rayleigh-wave arrivals and the misfit gradient at every iteration. This procedure, denoted as wave-equation Qs tomography (WQs), does not require the assumption of a layered model and tends to have fast and robust convergence compared to Q full waveform inversion (Q-FWI). Numerical examples with synthetic and field data demonstrate that the WQs method can accurately invert for a smoothed approximation to the subsur-face Qs distribution as long as the Vs model is known with sufficient accuracy.

Acoustic VTI wavefield tomography of P-wave surface and VSP data

Li, Vladimir; Tsvankin, Ilya; Guitton, Antoine; Alkhalifah, Tariq Ali (SEG Technical Program Expanded Abstracts 2017, Society of Exploration Geophysicists, 2017-08-17) [Conference Paper]

Transversely isotropic (TI) models have become standard in depth imaging and are often used in waveform inversion. Here, we develop a robust wave-equation-based tomographic algorithm for building acoustic VTI (transversely isotropic with a vertical symmetry axis) velocity models from P-wave surface reflection and vertical seismic profiling (VSP) data. Wavefield extrapolation is performed with an integral operator to avoid generating shear-wave artifacts. Focusing energy in extended images produced by reverse-time migration (RTM) makes it possible to update the zero-dip NMO velocity Vnmo and the anellipiticity parameter η. To constrain the anisotropy coefficient δ and improve the accuracy in Vnmo and η, we employ borehole information by introducing an additional objective-function term designed to fit VSP data. Image-guided smoothing is applied to both data- and image-domain gradients to steer the inversion towards geologically plausible solutions. Testing on the VTI Marmousi model shows that the joint inversion of surface and VSP data helps estimate all three relevant medium parameters.

Multiparameter Elastic Full Waveform Inversion With Facies Constraints

Zhang, Zhendong; Alkhalifah, Tariq Ali; Naeini, Ehsan Zabihi (SEG Technical Program Expanded Abstracts 2017, Society of Exploration Geophysicists, 2017-08-17) [Conference Paper]

Full waveform inversion (FWI) aims fully benefit from all the data characteristics to estimate the parameters describing the assumed physics of the subsurface. However, current efforts to utilize full waveform inversion as a tool beyond acoustic imaging applications, for example in reservoir analysis, faces inherent challenges related to the limited resolution and the potential trade-off between the elastic model parameters. Adding rock physics constraints does help to mitigate these issues, but current approaches to add such constraints are based on including them as a priori knowledge mostly valid around the well or as a boundary condition for the whole area. Since certain rock formations inside the Earth admit consistent elastic properties and relative values of elastic and anisotropic parameters (facies), utilizing such localized facies information in FWI can improve the resolution of inverted parameters. We propose a novel confidence map based approach to utilize the facies-based constraints in both isotropic and anisotropic elastic FWI. We invert for such a confidence map using Bayesian theory, in which the confidence map is updated at each iteration of the inversion using both the inverted models and a prior information. The numerical examples show that the proposed method can reduce the trade-offs and also can improve the resolution of the inverted elastic and anisotropic properties.

Wavefield separation by energy norm Born scattering

Sun, Bingbing; Alkhalifah, Tariq Ali (SEG Technical Program Expanded Abstracts 2017, Society of Exploration Geophysicists, 2017-08-17) [Conference Paper]

In Reflection Based Waveform Inversion, the gradient is computed by cross-correlating the direct and Born scattered wavefield with their adjoints applied to the data residuals. In this case, the transmitted part of the Born scattered wavefield produces high wavenumber artifacts, which would harm the convergence of the inversion process. We propose an efficient Energy Norm Born Scattering (ENBS) to attenuate the transmission components of the Born modeling, and allow it to produce only reflections. ENBS is derived from the adjoint of the Energy Norm (inverse scattering) imaging condition and in order to get deeper insights of how this method works, we show analytically that given an image, in which reflectivity is represented by a Dirac delta function, ENBS attenuates transmission energy perfectly. We use numerical examples to demonstrate that ENBS works in both the time and the frequency domain. We also show that in reflection waveform inversion (RWI) the wave path constructed by ENBS would be cleaner and free of high wavenumber artifacts associated with conventional Born scattering.

Waveform inversion for acoustic VTI media in frequency domain

Wu, Zedong; Alkhalifah, Tariq Ali (SEG Technical Program Expanded Abstracts 2016, Society of Exploration Geophysicists, 2016-09-06) [Conference Paper]

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 e to derive the relative reflected waveform inversion formulation. To reduce the number of parameters, we assume the background part of η = ε and work with a single variable to describe the anisotropic part of the wave propagation. Thus, the optimization variables are the horizontal velocity v, η = ε and the e perturbation. Application to the anisotropic version of Marmousi model with a single frequency of 2.5 Hz shows that this method can converge to the accurate result starting from a linearly increasing isotropic initial velocity. Application to a real dataset demonstrates the versatility of the approach.

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