Imaging under edges of salt sheets: A raytracing study

Muerdter, David R.; Lindsay, Richard O.; Ratcliff, Davis W.

doi:10.1190/1.1826707

Cited by 5 publications

(3 citation statements)

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“…That is, the workflow is equally valid if the medium is smooth without reflections (in this case the refraction (DC) TTT will be key to define the background), or if it has numerous reflections or few but separate ones, which according to their dimensions will be recovered with either TTT and/or FWI. Our synthetic results show that using our workflow even vertical V P boundaries and V P inversions, similar to those expected across steep faults or salt diapirs (in [9], [11], [41]), can be properly mapped with limited-offset data sets, but the maximum target depth to be resolved has to be evaluated from the V P structure and experiment design (Figs. 1, 4).…”

Section: Discussionmentioning

confidence: 89%

Toward a Practical Appraisal for Waveform Tomography of Band- and Offset-Limited Marine Seismic Data

Gras¹,

Tejero

Sallarès

et al. 2022

IEEE Trans. Geosci. Remote Sensing

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We present a generalized workflow to retrieve highresolution P-wave velocity (VP ) models of complex Earths subsurface structures from traditional marine near-vertical seismic reflection experiments. These records have typically offsets too short to map refraction phases and lack low frequency information. The workflow is composed of three steps: (1) downward continuation (DC) of seismic records to the seafloor to recover diving wave information; (2) travel-time tomography (TTT) of first arrivals obtained from DC data, to retrieve a kinematically correct model, and (3) full-waveform inversion (FWI) of the original streamer data set, starting with the model obtained with TTT and sequentially introducing higher wavenumber details into the model. We show that the TTT allows overcoming the issues associated to the non-linearity intrinsic to FWI. We also disentangle envelope and phase from the waveform to choose the objective function most suitable for FWI. We assess the accuracy of initial models and predict the quality of the FWI results by quantifying the early-arrival cycle skipping between original and simulated data. The efficiency of the workflow is tested with a challenging synthetic target model, containing vertical boundaries with a strong velocity contrasts and velocity inversions embedded in a checkerboard-like pattern. We show that workflow steps (1) and ( 2) provide a TTT model that is not cycle-skipped at the frequencies available in most marine seismic experiments, and thus allow step (3) FWI to obtain highresolution VP models of the subsurface using band-and offsetlimited field data sets, traditionally collected in marine airgun and streamer acquisitions.

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Section: Discussionmentioning

confidence: 89%

Toward a Practical Appraisal for Waveform Tomography of Band- and Offset-Limited Marine Seismic Data

Gras¹,

Tejero

Sallarès

et al. 2022

IEEE Trans. Geosci. Remote Sensing

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“…In media with lateral velocity variations, however, another important phenomena comes into play: lateral focusing and defocusing of the seismic wavefield. Even if the wavefield is regularly sampled on the surface, illumination below a complex salt structure may be sparse and irregular (Muerdter et al, 1996;Wyatt et al, 1997;Bear et al, 1999). Even U ¡ D shot-profile imaging conditions (Claerbout, 1971) based on deconvolving the downward-going source wavefield (D) from the upward-going receiver wavefield (U ) do not take into account limitations in the recording geometry that can also affect subsurface illumination.…”

Section: Introductionmentioning

confidence: 99%

Illumination‐based normalization for wave‐equation depth migration

Rickett

2003

GEOPHYSICS

168

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Illumination problems caused by finite-recording aperture and lateral velocity lensing can lead to biased amplitudes in migrated seismic images. I calculate weighting functions that compensate for illumination problems in wave-equation depth migration. The methodology takes into account reflector dip as well as both shot and receiver geometries, and because it is based on wave-equation migration, it naturally models the finite-frequency effects of wave propagation. The first step in the process is to model synthetic data with the true recording geometry over a reference model. Migrating the synthetic data then produces an image whose amplitude can be compared to the reference image to produce an illumination-based weighting function. These weighting functions can be applied directly to the migrated images to mitigate the effects of poor subsurface illumination. The reference model should be as close to the true model as possible; good choices include the migrated image, or a synthetic image with a single known dip that corresponds to the expected dip of a reflector of

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“…When such energy has not been recorded, due to its escape from the survey area or becoming evanescent (as it may at salt boundaries), the migrated image will have shadow zones (Muerdter et al, 1996) where the signal is weak or non-existent. Even improved migration methods such as downward continuation migration that generates angle-domain common image gathers (Prucha et al, 1999) cannot properly image such areas.…”

Section: Introductionmentioning

confidence: 99%

Regularized least‐squares inversion for 3‐D subsalt imaging

Clapp

Biondi

2005

SEG Technical Program Expanded Abstracts 2005

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SUMMARYObtaining seismic images of the subsurface near and beneath salt is very difficult due to seismic energy that is lost by propagating outside of the survey area or becoming evanescent at salt boundaries (poor illumination). We demonstrate an iterative regularized least-squares inversion for imaging that helps to compensate for illumination problems. We show the use of a regularization operator that acts to regularize amplitudes along reflection angles (or equivalent offset ray parameters) to compensate for the sudden, large amplitude changes caused by poor illumination. This regularization operator has the effect of filling in the gaps created in the reflection angle range due to the lost seismic energy. We discuss the use of this regularization operator in an iterative least-squares inversion scheme to improve imaging for a poorly illuminated 3-D seismic dataset. We introduce a new type of joint inversion problem that will allows us to simultaneously invert two or more datasets. For this iterative inversion scheme, we design a different regularization operator that allows us to share illumination information between images created from the different datasets involved. This regularized inversion allows us to create images that share the illumination information from the different datasets.

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Imaging under edges of salt sheets: A raytracing study

Cited by 5 publications

References 0 publications

Toward a Practical Appraisal for Waveform Tomography of Band- and Offset-Limited Marine Seismic Data

Toward a Practical Appraisal for Waveform Tomography of Band- and Offset-Limited Marine Seismic Data

Illumination‐based normalization for wave‐equation depth migration

Regularized least‐squares inversion for 3‐D subsalt imaging

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