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CWP Seminars - 2012 Spring

CWP seminars discuss topics pertaining to CWP's various research topics. These seminars are led by CWP faculty, staff and, on occasion, by external guest presenters.

CWP seminars are held on each Monday at 4 p.m. in the Green Center on the Colorado School of Mines campus.

 

Date Speaker(s) Title Abstract
4/9 thru 5/21 Project Review Meeting preparation and rehearsals - no seminars
4/2

Nishant

Nishant Kamath

Full-waveform inversion of multicomponent data for layered VTI media We extend FWI to multicomponent (PP and PS) data from anisotropic media, with the current implementation limited to a stack of horizontal, homogeneous VTI (transversely isotropic with a vertical symmetry axis) layers. I will go over the initial-model-building using nonhyperbolic semblance analysis and Dix-type equations. I will discuss the tests and analyses performed for data (PP+PS and pure PP) from 2 models. The tests include studying the influence of the initial model, spreadlength-to-depth ratio, random noise, and the kind of data used (pure PP or PP+PS), on inversion. Eigenvalue/eigenvector decomposition of the approximate Hessian matrix gives us some insight into the inversion results.
3/26

Andrew

Johannes Douma

TR optimization using deconvolution and its application to microseismic Johannes will demonstrate a technique to optimize the ability of time reversal to both spatially and temporally focus, or compress, elastic wave energy. It allows for optimization of time reversal focusing for any number of channels including one. Additionally, the speed, simplicity and robust nature of this process provides the ability to enhance applications currently using time reversal. It is then presented that this can cause improvements on microseismic event locating and future microseismic work by showing a comparison of spatial subsurface images created using deconvolution method versus time reversal method on the received signal to calculate a optimal back propagating signal.
3/19

Andrew

Francesco Perrone

Full wavefield tomography based on local image correlation The most popular velocity analysis and velocity model building procedures currently used are based on the invariance of migrated images with respect to the experiment index (shot number, plane-wave take-off angle, etc.) or extension parameters (reflection angle, correlation lags in extended images, etc.). All the information available, i.e. the entire survey, is used for assessing the quality of the model used for imaging the data. This approach is effective but forces a clear separation between imaging and velocity model building. In this presentation, we ask a complementary question: how much information about the velocity model is contained in a minimum number of images? Starting from an alternative statement of the semblance principle, we propose a measure of velocity error based on local correlations of pairs of migrated images. We design an objective function and implement a local, gradient-based optimization scheme to reconstruct the velocity model. Our methodology is "full-wave" because it is not based on a linearization of the imaging operator (in contrast with linearized wave-equation migration velocity analysis techniques). The gradient of the objective function is efficiently computed using the adjoint-state method.
3/12 CSM Spring Break - no seminar
3/5

Andrew

Andrew Munoz

Automatically tying well logs to seismic data Integrating well logs and seismic data has become an industry standard for interpretation workflows. Seismic data is recorded and commonly interpreted in vertical two-way time, and well logs, measured in depth, must be tied to seismic using a time-depth curve. However, well ties contain a large amount of uncertainty due to errors in the generation of synthetic seismograms and manual correlations of synthetic seismograms to seismic traces. Using dynamic time warping, an algorithm that optimally aligns two non-linear sequences, we quantitatively shift and warp synthetic seismograms with a corresponding seismic trace to produce an accurate time-depth curve.
2/27

ross_hill

N. Ross Hill, Chevron Energy Technology Corporation

Seismic applications of Beam Imaging techniques The separation of a recorded seismic wavefield into beam components that travel along raypaths is useful for many aspects of seismic imaging. First, forming images by beam summation has many advantages as a migration method. There are several additional processing and analysis steps that can be performed by beam methods. For example, the beam components can be analyzed to identify and process non-primary coherent events such as multiples. Also, the analysis of the beam components of seismic energy is useful during the estimation of seismic velocities.
2/20 President's Day - no seminar
2/13

Clement

Clément Fleury

Increasing illumination and sensitivity of reverse-time migration with internal multiples Reverse-time migration is a two-way time-domain finite-frequency technique that accurately handles the propagation of complex scattered waves and produces a band-limited high-frequency representation of the subsurface structure that is conventionally assumed to be linear in the model parameters. Because of this underlying linear single-scattering assumption, most implementations of this method paradoxically do not satisfy energy conservation and do not optimally use illumination and sensitivity of multiply scattered waves. Migrating multiply scattered waves requires preserving the nonlinear relation between image and model parameters. We modify the extrapolation of source and receiver wavefields to more accurately reconstruct multiply scattered waves. We extend the concept of imaging condition in order to map into the subsurface structurally coherent seismic events which correspond to the interaction of both singly and multiply scattered waves. This results in an imaging process that we refer to as nonlinear reverse-time migration. We propose a strategy to analyze separated contributions to the final nonlinear image. Our goal is to provide a new tool suitable for seismic interpretation and potentially migration velocity analysis that benefits from increased illumination and sensitivity from multiply scattered seismic waves. Our method noticeably applies to migrating internal multiples which is a clear advantage for imaging challenging complex subsurface features, e.g., in salt and basalt environments. We illustrate our technique with synthetic seismic imaging experiments; one of which includes a subsalt imaging example.
2/6

Steve

Steve Smith

Global inversion method for compaction-induced traveltime shifts from multicomponent seismic data Analysis of compaction-induced time shifts estimated from coupled geomechanical and multicomponent seismic modeling demonstrates that changing stiffness coefficients generate elliptical anisotropy and time-shift values that vary with reservoir depth, reflector proximity to the reservoir, and the wavetype used for the measurement. P-wave time shifts demonstrate offset dependency at reflection points around the reservoir, while much larger (sensitive) S-wave time shifts occur at reflection points primarily below the reservoir. Converted waves exhibit a combination of these effects. He discusses an inversion methodology intended to exploit and qualify the sensitivity of each wavetype (P, S, PS) around compacting reservoir using our established modeling process and resulting time shifts at reflectors above, below, and at the top interface of the reservoir. Fast-approximation modeling is used for development and testing. An interval bisection method similar to genetic or "nearest neighbor" algorithms results in fast convergence while exploring and establishing misfit for a wide range of parameter values (in this case reservoir pressure). He will demonstrate the procedure for the approximation models. Inversion results on geomechanical/elastic models should demonstrate the most sensitive combinations of wavetype and reflector proximity for estimating the pressure values inside the reservoir, and compaction induced stress in the overburden.
1/30

Ashley

Ashley Fish

Effects of microseimsic aperture and velocity model accuracy with respect to automatic wavefield-based event detection Picking arrivals in noisy microseismic data is not always possible, but it is a reality faced by the industry. To overcome the difficulties associated with picking arrivals, we advocate for automatic techniques based on reverse time imaging which eliminate the need for arrival identification. Reverse time imaging is capable, in principle, to focus microseismic energy at its source position and at its trigger time, even when data are corrupted by high levels of noise. However, time-reverse focusing relies on a good understanding of the models used for wave propagation, as well as on a broad acquisition aperture. We explore the benefits and pitfalls associated with reverse time imaging and emphasize the need for wide aperture in microseismic acquisition.
1/23 Brad Artman, Spectraseis

Spectraseis: new research projects

Spectraseis is a provider of microseismic and ambient wave field surveys to the oil and gas industry. After relocating from Zurich last year, Spectraseis is continuing a history of industry-academic partnership projects with the launch of a new consortia with CWP and other academic and industry collaborators. We will present the concept and participants in the project and explain a range of potential projects to pursue within the 3 year project that will acquire a unique shared data set the first year to allow in-depth research for the duration of the project.

 

 

 

 

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