Migration-velocity analysis using image-space generalized wavefields

Abstract

An accurate depth-velocity model is the key for obtaining good quality and reliable depth images in areas of complex geology. In such areas, velocity-model definition should use methods that describe the complexity of wavefield propagation, such as focusing and defocusing, multiple arrivals, and frequency-dependent velocity sensitivity. Wave-equation tomography in the image space has the ability to handle these issues because it uses wavefields as carriers of information. However, its high cost and low flexibility for parametrizing the model space has prevented its routine industrial use.This thesis aims at overcoming those limitations by using new wavefields as carriers of information: the image-space generalized wavefields. These wavefields are synthesized by using a pre-stack generalization of the exploding-reflector model. Cost of wave-equation tomography in the image space is decreased because only a small number of image-space generalized wavefields are necessary to accurately describe the kinematics of velocity errors and because these wavefields can be easily used in a target-oriented way. Flexibility is naturally incorporated into wave-equation tomography in the image space by using these wavefields because their modeling have as the initial conditions some key selected reflectors, allowing a layer-based parametrization of the model space.To use the image-space generalized wavefields in wave-equation tomography in the image space, the method is extended from the shot-profile domain to the image-space generalized-sources domain. In this new domain, the velocity updates are very fast. ER denotes Easily Reproducible and are the results of processing described in the paper. The author claims that you can reproduce such a figure from the programs, parameters, and makefiles included in the electronic document. The data must either be included in the electronic distribution, be easily available to all researchers (e.g., SEG-EAGE data sets), or be available in the SEP data library 2 . We assume you have a UNIX workstation with Fortran, Fortran90, C, X-Windows system and the software downloadable from our website (SEP synthetic data examples associated with this report are classified as NR because they were generated externally to SEP and only the results were released by agreement.Our testing is currently limited to LINUX 2.6 (using the Intel Fortran90 I thank Biondo Biondi, my adviser, for always being a source of encouragement and a reference on academic honesty. His attitude made clearer to me both the importance of obtaining good results and the usefulness of the bad ones, which deserve to be brought to light. I thank Jon Claerbout for initiating us students into the mysteries of inverse problems and for sharing his contagious enthusiasm for doing research. I admire his energy, curiosity, and serendipity. Bob Clapp has constantly been steps ahead of everyone in looking for computational solutions that best fit the type and size of geophysical problems we propose to solve. Also, his knowledge about ...

Subsalt velocity analysis by target‐oriented wavefield tomography: A 3‐D field‐data example

“…To reduce the cost and increase the flexibility of wavefield-based tomography, Biondi (2006); Guerra (2010); Tang and Biondi (2010) originated the idea of targetoriented wavefield tomography. The idea is to synthesize a target-oriented new data set specifically for velocity analysis.…”