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Results
ABSTRACT Multiple-scattered waves contain information that is commonly disregarded during imaging and tomography. Marchenko wavefields are superior to time-reverse wave-fields by handling primaries together with internal and surface-related multiples. Using all types of waves for imaging can greatly improve the illumination and augment the sensitivity of the data to errors in the background velocity model. We compare extended images computed with reverse time and Marchenko wavefields, and investigate the potential of using multidimensional deconvolution for extended images in order to obtain higher image resolution. Our experiments show that the Marchenko wavefields are sensitive to errors in the background model in a way that is similar to the sensitivity of time-reverse wavefields. The main difference between these imaging strategies is the improved angle illumination with the Marchenko wavefields due to the correct use of multiples; this improvement can eliminate the bias of tomography operators towards lower velocities when the data are contaminated with multiples. Presentation Date: Monday, October 17, 2016 Start Time: 1:25:00 PM Location: 142 Presentation Type: ORAL
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.90)
ABSTRACT Two-way wavefields generated with the Marchenko method are able to reproduce complex wave phenomena that includes primaries, internal multiples and surface-related multiples. The wavefield contains reflections and information from the true model, but propagating with the kinematics of an input background velocity model. We design an inverse problem to find a model that explains the scattering phenomena present in the reconstructed wavefield. The two-way nature of the Marchenko wavefields allows us to use them with the homogeneous wave equation and obtain images that are indicative of subsurface model parameters. Unlike conventional imaging methods, where the image is indicative of the interfaces in the subsurface, our method inverts for the properties within the subsurface. Our tests show that one can invert for images indicative of the true model even when the background velocity model is partially inaccurate. Furthermore, we are able to image properties from the true model that are not part of the inputs used to generate the wavefield. Presentation Date: Wednesday, October 19, 2016 Start Time: 2:20:00 PM Location: 155 Presentation Type: ORAL
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.91)
Gradient computation for VTI acoustic wavefield tomography
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))
ABSTRACT 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
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (0.97)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.90)
ABSTRACT A major challenge for multiparameter full-waveform inversion (FWI) is the inherent trade-offs (or cross-talk) between model parameters. Here, we perform FWI of multicomponent data generated for a synthetic VTI (transversely isotropic with a vertical symmetry axis) model based on a geologic section of the Valhall field. A horizontal displacement source, which excites intensive shear waves in the conventional offset range, helps provide more accurate updates to the SV-wave vertical velocity. We test three model parameterizations, which exhibit different radiation patterns and, therefore, create different parameter trade-offs. The results show that the choice of parameterization for FWI depends on the availability of long-offset data, the quality of the initial model for the anisotropy coefficients, and the parameter that needs to be resolved with the highest accuracy. Presentation Date: Monday, October 17, 2016 Start Time: 2:15:00 PM Location: 166 Presentation Type: ORAL
- Europe > United Kingdom > North Sea > Central North Sea > Moray Firth > Moray Firth Basin > Moray Firth Basin > Witch Ground Graben > P.213 > Block 16/26a > Brae Field > Alba Field > Caran Sandstone Formation (0.99)
- Europe > United Kingdom > North Sea > Central North Sea > Moray Firth > Moray Firth Basin > Moray Firth Basin > Witch Ground Graben > P.213 > Block 16/26a > Brae Field > Alba Field > Alba Sandstone Formation (0.99)
- Europe > United Kingdom > North Sea > Central North Sea > Moray Firth > Moray Firth Basin > Fladen Ground Spur > Witch Ground Graben > P.213 > Block 16/26a > Brae Field > Alba Field > Caran Sandstone Formation (0.99)
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