A Technique for Joint Determination of Lateral Velocity Variations and Azimuthal Anisotropy for Surface Waves

2013 ◽  
pp. 200-209
Author(s):  
T. B. Yanovskaya
Keyword(s):  
Surface Waves ◽  
Azimuthal Anisotropy ◽  
Lateral Velocity ◽  
Joint Determination ◽  
Velocity Variations

scholarly journals Stable wide‐angle Fourier finite‐difference downward extrapolation of 3‐D wavefields

Geophysics ◽  
2002 ◽  
Vol 67 (3) ◽  
pp. 872-882 ◽  
Author(s):  
Biondo Biondi
Keyword(s):  
Finite Difference ◽  
Continuation Method ◽  
Phase Error ◽  
Azimuthal Anisotropy ◽  
Laplacian Operator ◽  
Lateral Velocity ◽  
Data Set ◽  
Frequency Dependent ◽  
Reference Velocity ◽  
Velocity Variations

I present an unconditionally stable, implicit finite‐difference operator that corrects the constant‐velocity phase‐shift operator for lateral velocity variations. The method is based on the Fourier finite‐difference (FFD) method. Contrary to previous results, my correction operator is stable even when the medium velocity has sharp discontinuities, and the reference velocity is higher than the medium velocity. The stability of the new correction enables the definition of a new downward‐continuation method based on the interpolation of two wavefields: the first wavefield is obtained by applying the FFD correction starting from a reference velocity lower than the medium velocity; the second wavefield is obtained by applying the FFD correction starting from a reference velocity higher than the medium velocity. The proposed Fourier finite‐difference plus interpolation (FFDPI) method combines the advantages of the FFD technique with the advantages of interpolation. A simple and economical procedure for defining frequency‐dependent interpolation weight is presented. When the interpolation step is performed using these frequency‐dependent interpolation weights, it significantly reduces the residual phase error after interpolation, the frequency dispersion caused by the discretization of the Laplacian operator, and the azimuthal anisotropy caused by splitting. Tests on zero‐offset data from the SEG‐EAGE salt data set show that the FFDPI method improves the imaging of a fault reflection with respect to a similar interpolation scheme that uses a split‐step correction for adapting to lateral velocity variations.

3D velocity-independent elliptically anisotropic moveout correction

Geophysics ◽  
2009 ◽  
Vol 74 (5) ◽  
pp. WB129-WB136 ◽  
Author(s):  
William Burnett ◽  
Sergey Fomel
Keyword(s):  
Field Data ◽  
Azimuthal Anisotropy ◽  
Three Dimensions ◽  
Velocity Analysis ◽  
Lateral Velocity ◽  
Analysis Techniques ◽  
West Texas ◽  
Imaging Approach ◽  
Velocity Variations ◽  
Seismic Images

Azimuthal anisotropy or lateral velocity variations cause azimuthal variations in moveout velocity, which can degrade seismic images if handled improperly. In cases in which apparent azimuthally anisotropic moveout is present, a single picked velocity is inadequate to flatten an event on a 3D CMP gather. Conventional velocity-analysis techniques require a significant amount of time and effort, especially in areas where apparent anisotropy is observed. We propose a velocity-independent imaging approach to perform an elliptically anisotropic moveout correction in three dimensions. The velocity-independent approach relies on volumetric local traveltime slopes rather than aggregate velocities and therefore provides an azimuthally flexible description of traveltime geometries throughout the gather. We derive theoretical expressions for extracting the moveout slowness matrix and the angle between the symmetry and acquisition axes as volumetric local attributes. A practical inversion scheme to extract the same parameters is also developed. These parameters are used to solve for moveout slowness as a function of azimuth. Tests on a synthetic common-midpoint (CMP) gather show accurate results for the automatic moveout correction and the inversion scheme. A field data example from west Texas illustrates the application of the automatic moveout correction as a residual moveout.

Reliability of data-driven wavefront attributes in laterally heterogeneous media

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. O49-O62
Author(s):  
Yujiang Xie ◽  
Dirk Gajewski
Keyword(s):  
Heterogeneous Media ◽  
Data Driven ◽  
Velocity Variation ◽  
Good Match ◽  
Lateral Velocity ◽  
Model Driven ◽  
Automatic Picking ◽  
Velocity Variations ◽  
Velocity Changes

3D wavefront attributes play a major role in many processing steps, such as prestack data enhancement, diffraction separation, and wavefront tomography. For the determination of the 3D wavefront attributes, various stacking operators can be used by adopting semblance optimization. These operators are derived for laterally homogeneous media. In praxis, however, they are applied in real geologic environments with even strong lateral velocity variations such as salt structures. This leads to the question of the quality of the 3D wavefront attributes using these operators when determined in the presence of strong lateral velocity changes. We compared the 3D wavefront attributes determined by 3D common-reflection-surface (CRS) operator (called data-driven wavefront attributes) with the 3D wavefront attributes computed by 3D kinematic and dynamic ray tracing (called model-driven wavefront attributes). For the determination of the 3D CRS wavefront attributes, we have developed a global optimization scheme based on differential evolution. Reflection seismic data of the laterally heterogeneous 3D SEG C3WA salt model are considered, and the model-driven wavefront attributes are computed for a smoothed version of the 3D SEG salt model. The comparison reveals that the wavefront attributes for the normal-incidence-point ray indicate a very good match not only in areas of mild lateral velocity variation but even in regions with strong lateral velocity variations. Approximately 80%–90% of the total picks indicate the good match with a relative error of less than 10% when a semblance threshold of 0.1 is considered in the automatic picking process. This confirms the validity of the determined wavefront attributes even in the presence of strong lateral velocity changes. Using a higher semblance threshold in the automatic picking leads to fewer picks but with an even better match between model- and data-driven wavefront attributes.

On the joint determination of biological and economic systems

2002 ◽  
Vol 42 (1-2) ◽  
pp. 301-311 ◽  
Author(s):  
Chad Settle ◽  
Thomas D. Crocker ◽  
Jason F. Shogren
Keyword(s):  
Economic Systems ◽  
Joint Determination

Tracking of velocity variations at depth in the presence of surface velocity fluctuations

Geophysics ◽  
2013 ◽  
Vol 78 (1) ◽  
pp. U1-U8 ◽  
Author(s):  
Benoit de Cacqueray ◽  
Philippe Roux ◽  
Michel Campillo ◽  
Stefan Catheline
Keyword(s):  
Surface Waves ◽  
Body Waves ◽  
Surface Velocity ◽  
Small Scale ◽  
Beam Forming ◽  
Near Surface ◽  
Velocity Fluctuations ◽  
Wave Separation ◽  
Double Beam ◽  
Velocity Variations

We tested a small-scale experiment that is dedicated to the study of the wave separation algorithm and to the velocity variations monitoring problem itself. It handles the case in which velocity variations at depth are hidden by near-surface velocity fluctuations. Using an acquisition system that combines an array of sources and an array of receivers, coupled with controlled velocity variations, we tested the ability of beam-forming techniques to track velocity variations separately for body waves and surface waves. After wave separation through double beam forming, the arrival time variations of the different waves were measured through the phase difference between the extracted wavelets. Finally, a method was tested to estimate near-surface velocity variations using surface waves or shallow reflection and compute a correction to isolate target velocity variations at depth.

Sign in / Sign up

Export Citation Format

Share Document