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CWP Seminars - 2015 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:

A-Team seminars

C-Team seminars

iTeam seminars

Steam seminars

 

Fall 2015 CWP seminars

Date Speaker(s) Title Abstract
12/14

No seminar - Mines winter semester final exams

12/7

E;oas Arias

Elias Arias

1) A simple approach to image guided inversion


2) Turning seismic images into usable seismic data using machine learning

1) Ideally, the solution to an inverse problem would penalize not only derivatives along the axes of the model, but also penalize the derivatives along the structure of a model. To include such a term, we must first find a way to determine the structure of a model. Hale (2009) describes a way to delineate structure from an image using structure tensors. The structural information can be used in the model objective function to penalize large derivatives in the direction parallel to structure along the model. For the simple example shown in this talk, the model obtained using structural information better honors the shape of the anomaly.

2) The creators and contributors to the Madagascar software package, SEG, and others promote reproducibility. However, seldom do authors provide the data that produced the results in their paper. In this talk, I will describe a method for turning pictures or screenshots of seismic images into seismic data. We first build a library of color bars in RGB space. Then, using self organizing maps we can determine the color bar that best fits the image. Finally, we add values to the color bar and match colors to the image to obtain usable seismic data. The implications of the work presented include borrowing interesting seismic images for one's own research and further pushing the limits of reproducibility.

11/30

Thomas Planès

Thomas Planès

CWP Visiting Scholar

Can we create a virtual source in the deep earth?

An informal discussion of a research idea, about the possibility of creating a virtual seismic source in the deep earth.

11/23

Hui Wang

Hui Wang

Some aspects of low-rank modeling in orthorhombic media

Low-rank based wave equation modeling seems a good candidate for the waveform inversion engine in orthorhombic media. I will discuss several aspects of the low-rank modeling in orthorhombic media, including the adjoint mode modeling, absorbing boundary condition, and the parallelism of implementations. Tutorial examples will be given to illustrate the concepts and some migrated images will be shown to test the adjoint modeling codes.

11/16

Yuting Duan

Yuting Duan

Time-lapse azimuthal depth shift analysis

Time-lapse (4D) seismic is focused on production and changes in the reservoir, and it plays an important role in reservoir management. This presentation will focus on understanding and expanding the use of azimuthal data for 4D interpretation. The study of the subsurface illumination shows that the quality of partial azimuthal images is strongly affected by the acquisition geometry. This depthshift analysis will be focused on a specific target in the data. Using partial azimuth stacks instead of the full stack of all azimuths, I show the possibility to more precisely define the boundaries of 4D depthshift anomalies.

11/9

Chris Graziano

Chris Graziano

Compressional and converted wave data evaluation at Bell Creek

The Bell Creek oil field is located in the southern part of Montana in the Powder River Basin. The field was discovered in 1967 and heavily drilled, which resulted in 530 wells by 1969. What was thought to be a simple field to produce, ended up being a highly compartmentalized field. When flooding the field with CO2, which is what Denbury Resources specializes in, the boundaries between compartments needs to be known to help explain why certain wells are not communicating with each other. Through the use of well logs and PP seismic data, the boundaries between different compartments can be better identified than when simply well logs are used. Also, the use of PS seismic data can help shed some more light on rock quality issues at the Bell Creek oil field.

11/2

CWP faculty and students

Reflections of 2015 SEG Annual Meeting

CWP students will each present a brief overview of the presentations s/he attended during the 2015 SEG Annual Meeting.

10/26

Michael Wakin

Michael Wakin

Associate Professor,
Dept. of Electrical Engineering and Computer Science,
Colorado School of Mines

An overview of compressive sensing

A great deal of attention has been paid to developing effective low-dimensional models for the structure inherent in high-dimensional signals. Indeed, such models are key to addressing the growing challenges of acquiring, storing, and processing ever larger and higher resolution data sets. Recently, an exciting byproduct of this work has been the emergence of a field known as Compressive Sensing (CS). CS is based on the revelation that certain high-dimensional signals obeying low-dimensional models can actually be recovered from small numbers of nonadaptive (even random) linear measurements. In this talk I will provide an introduction to CS and survey some its many potential applications, both within and outside of geophysics.

10/19

No seminar - 2015 SEG Annual Meeting

10/12

Satyan Singh

Satyan Singh

Marchenko imaging and application of the Green's function for virtual source and reciever wavefield reconstruction

Imagine placing a receiver at any location in the Earth and recording the response at that location to sources on the surface. In such a world, we could place receivers around our reservoir to better image the reservoir and understand its properties. Realistically, this is not a feasible approach for understanding the subsurface. Here, we present an alternative and realizable approach to obtaining the response of a buried virtual receiver for sources at the surface. This method, called autofocusing, is capable of retrieving the Green's function for a virtual point in the subsurface to the acquisition surface. In our case, a physical receiver is not required at the subsurface point; instead, we require the reflection measurements for sources and receivers at the surface of the Earth and a macro-model (no small-scale details of the model are necessary). We can interpret the retrieved Green's function as the response to sources at the surface for a virtual receiver in the subsurface. We obtain this Green's function by solving the Marchenko equation, an integral equation pertinent to inverse scattering problems. Our derivation of the Marchenko equation for the Green's function retrieval takes into account the free-surface reflections. At today's CWP seminar I will show some examples of Marchenko imaging and also a new application of using the Green's function for virtual source and reciever wavefield reconstruction. With time pending I will also discuss the intuition behind the Marchenko equations.

10/5

Vladimir Li

Vladimir Li

Gradient calculation for image-domain wavefield tomography in acoustic VTI media

I will first talk about my short visit to Tongji University in Shanghai this August and briefly describe the research of the Dr. Jiubing Cheng's group at Tongji. After that, I will discuss gradient calculation for image-domain wavefield tomography in acoustic VTI media and show the gradients for anisotropy parameters obtained with the first-order adjoint-state method. I will mention the influence of these parameters on the residual moveout in the image domain and discuss the challenges of the VTI parameter estimation from P-wave reflections. As one of the solutions, I will show the derivations of the Hessian-vector product using the second-order adjoint-state method. Incorporating Hessian into parameter estimation is supposed to help compensate for illumination and mitigate the tradeoff between model parameters, which could be particularly relevant for multi-parameter inversion.

9/28

John Scales

John Scales

Professor,
Department of Physics,
Colorado School of Mines

Non-contacting ultrasonic and electromagnetic measurements of waves

 

In this talk I will give an overview of the technology we use to excite and measure ultrasonic and electromagnetic waves of sub-millimeter wavelength in in solids, liquids and gases. The focus of our work is both material characterization and fundamental studies of waves in random media as it relates to quantum or wave chaos. I will show applications in both areas.

 

9/21

Daniel Rocha, Jr.

Daniel Rocha, Jr.

Elastic wavefield imaging using the energy norm

From the elastic wave equation and the energy conservation principle, we derive an energy norm that is applicable to imaging with elastic wavefields. Extending the concept of the norm to an inner product enables us to compare two related wavefields. For example, the inner product of source and receiver wavefields at each spatial location leads to an imaging condition. This new imaging condition outputs a single image representing the total reflection energy, and contains individual terms related to the kinetic and potential energy (strain energy) from both extrapolated wavefields. An advantage of the proposed imaging condition compared to alternatives is that it does not suffer from polarity reversal at normal incidence, as do conventional images obtained using converted waves. Our imaging condition also accounts for the directionality of the wavefields in space and time. Based on this information, we modify the imaging condition for attenuation of backscattering artifacts in elastic reverse-time migration images. Numerical experiments show the quality of the energy images compared to their conventional counterparts, and the effectiveness of the imaging condition in attenuating backscattering artifacts even in media characterized by high spatial variability.

9/14

Elias Arias

Elias Arias

Estimating slopes - an integration of smooth dynamic warping at PGS

Image enhancing processes and filters require accurate estimates of reflection slopes. Areas in an image containing steep, conflicting, or rapid changes in slope, or areas with high noise have proven difficult to accurately estimate using current methods. Slope estimates in these areas often contain undesirable discontinuities that introduce errors in the processes and filters that use them as input. By adapting the smooth dynamic warping algorithm to estimate slopes, we constrain the change in slope which prevents these undesirable discontinuities. As compared to the current methods for slope estimation, smooth dynamic warping requires more user input through additional parameters. These parameters allow the user to balance the smoothness of the solution, and the time and memory required to compute the solution. Different combinations of parameters demonstrate how faster solutions produce less smooth results that require more computer memory.

9/7

Thomas Planès

Thomas Planès

CWP Visiting Scholar

Monitoring the tidal response of a sea levee with ambient seismic noise

Internal erosion, a major cause of failure of earthen dams and levees, is often difficult to detect at early stages using traditional visual inspection. The passive and non-invasive seismic interferometry technique could enable the detection of internal changes taking place within these structures. The technique is here tested on the Dutch sea levee of Colijnsplaat, which presents signs of concentrated seepage in the form of sandboils. Using passive ambient seismic data collected over a 12 hour period, surface waves propagating along the levee are reconstructed through seismic interferometry. Two dominant ambient seismic noise sources are identified, the traffic on the Zeeland bridge and a nearby wind turbine. Time lapse variations of the surface wave velocities are then computed during the 12 hour tidal cycle for different frequency bands, i.e. depth ranges. The velocity variations correlate with on site pore water pressure measurements. Some spatially localized relative velocity variations of up to 5% are observed.

8/31

Antoine Guitton

Antoine Guitton

Stanford University

Full or not-so-full waveform inversion?

In the past few years, the number of Full Waveform Inversion (FWI) applications and results has increased dramatically with the premise that FWI can yield high resolutions models. However, given the number of approximations that are being made by practitioners to make FWI feasible, are high resolution models a wishful thinking or a tangible goal to attain? It is my observation that the best FWI results with the most impact on imaging are usually coming from the inversion of medium/long wavelengths of the model, inverting mostly long offsets, post-critical events or diving waves. Results showing a high degree of details in the velocity model, one of the selling points of FWI, are often questionable. For an acoustic medium parameterized with both Vp and density, this talk will review basic principles of FWI and one of its pitfalls: the inherent ambiguity between Vp and density, especially at short offsets. The importance of "parameterization" will also be discussed.

1st CWP seminar of the Fall 2015 semester (CWP administrative topics)

 

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