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CWP Seminars - 2014 Fall

CWP seminars discuss topics pertaining to our broad areas of research interests. These seminars are led by CWP faculty, students and, on occasion, by guest presenters. CWP seminars are held every Monday at 4 p.m. in the Green Center on the Colorado School of Mines campus. Click here to see previous CWP Seminars.

Note: To view weekly seminar schedules of individual CWP teams, click a link below:

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Fall 2014 CWP seminars

Date Speaker(s) Title Abstract
10/20 SEG Annual Meeting discussion (CWP administrative topics)


Vladimir Kazei

Spectral sensitivities technique for full-waveform inversion

I extend a technique originally proposed for diffraction tomography spectral coverage analysis (Devaney, 1984) to sensitivity analysis. After investigating the spectral resolution possibilities of full-wavefield in several horizontally uniform models I show some general consequences on roles of several types of waves for full-waveform inversion applications. The results on the role of free surface multiples obtained I discuss in details and suggest a preconditioning algorithm exploiting the spectral sensitivities technique.


No seminar - CSM Fall Break



Yuting Duan

A scalar imaging condition for elastic reverse-time migration

Polarity changes in converted-wave images constructed by elastic reverse-time migration cause destructive interference when stacking images computed for different experiments in a seismic survey. We derive a simple imaging condition for converted waves to correct the image polarity and reveal the conversion strength from one wave mode to another. Compared to alternative methods for correcting polarity reversals in PS and SP images, our imaging condition is simple and robust, and does not add significantly to the cost of reverse-time migration. Our imaging condition requires computing the divergence and curl of source P and S wavefields, respectively, which provide information regarding the directionality of the wavefields. However, computing the gradient and curl distorts the amplitude spectrum as well as the phase of the wavefields, and as a result, it distorts the amplitude and phase of the migrated images. We design a simple filter to correct for this ampli!
tude and phase distortion. In addition, this filter can also be applied to correct for the amplitude and phase distortion resulting from the Helmholtz decomposition, which also involves the computation of the divergence and curl of wavefields.



Ali Knaak

Error propagation with synthetic aperture for CSEM

Controlled-source electromagnetics (CSEM) is a geophysical method used to de-risk and find hydrocarbon reservoirs in marine settings. The size of the target, low resolution, and the depth of the target limit the detection of the target by the method. I have previously shown how the technique of optimally weighted synthetic aperture applied to CSEM responses increases the detectability and resolution of reservoirs. In the seminar, I will show how we have incorporated error propagation theory into our optimization method to decrease the level of noise while still increasing the anomaly from the reservoir. I will demonstrate the benefits of the optimization with synthetic electromagnetic responses.




Xinming Wu

Horizon volumes and unconformities

I will discuss two methods for constructing seismic horizons. The first method generates horizons one at a time; the second generates an entire volume of horizons at once. Rather than gradually building a horizon by extending one or more seed points to a surface along seismic reflectors, both of the two methods generate horizons by solving partial differential equations. The most significant new aspect of both methods is the ability to interactively specify a small number of control points to more accurately construct horizons. I will also discuss a 3D method to automatically detect unconformities from a seismic image, then use the detected unconformities as constraints to more accurately estimate seismic normal vectors at unconformities, and better flatten seismic images containing unconformities. All methods were implemented when I worked at Transform Software/Drillinginfo last summer.



Tariq Alkhalifah

FWI+MVA the natural way

Integrating migration velocity analysis (MVA) and full waveform inversion (FWI) can help reduce the high nonlinearity of the classic FWI objective function. The combination of inverting for the long and short wavelength components of the velocity model using a dual objective function that is sensitive to both components is still very expensive and have produced mixed results. We develop an approach that includes both components integrated to complement each other. We specifically utilize the image to generate reflections in our synthetic data only when the velocity model is not capable of producing such reflections. As a result, we get the MVA working when we need it, and mitigate it's influence when the velocity model produces accurate reflections (possibly first for the low frequencies). This is achieved using a novel objective function that includes both objectives. Applications to a layered model, as well as, the Marmousi model demonstrate the approach main features.



Hui Wang

Prestack exploding reflector modeling and migration in TI media

Prestack depth migration in anisotropic media, especially those that exhibit tilt, can be costy using reverse time migration (RTM). I will present a two-way spectral wavefield extrapolation using prestack exploding reflector model (PERM) in acoustic transversely isotropic (TI) media. This technique can naturally export the common image gathers compared to cross-correlation imaging condition and poynting vectors approaches. I construct systematic ways to evaluate phase angles and phase velocities in dip oriented TI (DTI), vertical TI (VTI) and tilted TI (TTI) media, which are required by the spectral time-steppings of wavefields. I will show migration results from the Marmousi VTI model and the BP2007 TTI model.



Chinaemerem Kanu

Sensitivity to time-lapse velocity change using multiply elastic scattered waves

Multiply scattered waves provide the potential for increased illumination or increased detectability of the weak perturbations presence within a medium. One of the proven use of the multiply scattered waves is in the detection of the weak time-lapse changes, such as velocity changes due geomechanical processes within the sub-surface or localized defects/cracks within mechanical structures. However, using multiply scattered waves to resolve localized weak changes within a medium requires the characterization of the distribution of the scattered waves within the medium. In a couple of meetings back we explored the characteristics of acoustic sensitivity kernel that can be used to resolve weak changes within a scattering medium. In this presentation, we will look at the computation of the elastic sensitivity kernels and explore their characteristics.


1st CWP seminar of the Fall 2014 semester (CWP administrative topics)


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