(Seminar for Fall, 2011)
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Date |
Speaker |
Subject |
Notes |
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01/24/12 |
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Round table meeting. |
Discussion about work done and proposed work. |
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01/31/12 |
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. |
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02/07/12 |
Pengfei Cai. |
Joint velocity analysis of PP- and PS-waves for TI media. |
He implements the "PP+PS=SS" method to produce pseudo shear data. Then he flattens the PP and SS CIGs generated from PSDM and tie PP image and SS image. His algorithm has been tested on a layered VTI model and a more complicated model will be presented. |
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02/14/12 |
Round table meeting. |
Discussion about work done and proposed work. |
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02/21/12 |
Round table meeting. |
Discussion about work done and proposed work. |
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02/28/12 |
Bharath Shekar. |
Real ray tracing in anisotropic viscoelastic media. |
He will discuss the algorithm presented in Vavrycuk (2008) for ray tracing in anisotropic viscoelastic media. Anisotropic viscoelastic media are commonly characterized by frequency dependent complex stiffness coefficients. The Eikonal equation for such media is a non-linear partial differential equation in the complex plane. This is handled by complex ray theory, which treats rays as trajectories in complex space (e.g., Thomson, 1997). However, material properties are specified for real space, and this complicates application of complex ray theory to practical problems. Vavrycuk (2008) proposes a method which treats rays as trajectories in real space. He presents ray tracing equations for anisotropic viscoelastic media that satisfy the complex Eikonal equation approximately. In this setting, the complex energy velocity vector is homogeneous. The slowness vector which makes the complex energy velocity vector homogeneous is called the stationary slowness vector. The stationary slowness vector may be inhomogeneous. Bharath will briefly discuss the above concepts, and show ray tracing examples for homogeneous and heterogeneous anisotropic attenuative media. In his numerical examples for smooth media, he finds that the inhomogeneity angle of the stationary slowness vector is small (the maximum value is within 5 degrees). Vavrycuk's (2008) algorithm is for ray tracing in cartesian coordinates. In order to compute geometrical spreading, it is necessary to perform dynamic ray tracing. However, since attenuation does not have a significant influence on geometrical spreading, the geometrical spreading factor may be computed for the reference elastic media. In summary, for the purposes of inversion for attenuation (if the velocity field is known), it is sufficient to perform dynamic ray tracing in elastic media once, followed by multiple iterations of ray tracing in viscoelastic media. |
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03/06/12 |
Bharath Shekar. |
Real ray tracing in anisotropic viscoelastic media. |
Numerical examples of previous week's talk. |
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03/20/12 |
No meeting (Spring Break). |
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03/27/12 |
Natalya Patrikeeva. |
Sensitivity analysis of wide-azimuth angle decomposition in isotropic and TI media. |
She extends a technique of Sava and Alkhalifah for wide-azimuth angle decomposition for general TI media. Natalya decomposes extended CIPs into angle gathers but also preserves the time-lag axis. Gathers are constructed with correct model and incorrect model parameters. She performs sensitivity analysis for incorrect velocity, anisotropic parameter eta, and TI symmetry axis. This sensitivity analysis will allow her to determine which parameter is the most relevant for wide-azimuth angle decomposition in general TI medium. |
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04/03/12 |
No meeting. |
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04/10/12 |
No meeting (Rehearsal). |
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04/17/12 |
No meeting (Rehearsal). |
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04/24/12 |
No meeting (Rehearsal). |
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05/01/12 |
No meeting (Rehearsal). |
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05/08/12 |
No meeting. |