In areas of complex geology, migration-velocity analysis (MVA) should use methods that describe the complexity of wavefield propagation, such as focusing and defocusing, multipathing, and frequency- dependent velocity sensitivity. MVAby wavefield extrapolation has the ability to address these issues because it uses wavefields as carriers of information. However, its high cost and lack of flexibility with respect to model parametrization have prevented its routine industrial use. We overcome those limitations by using new wavefields: the image-space generalized wavefields. These wavefields are synthesized from a prestack image computed with wavefield-extrapolation methods, using the pre-stack exploding-reflector model. Cost of MVAby wavefield extrapolation 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 because modeling these wavefields have selected reflectors as the initial conditions, allowing the use of a horizon- based parametrization of the model space. In a 3D real data example, we show that using wavefields synthesized by the prestack exploding-reflector model greatly improves efficiency of migration-velocity analysis by wavefield-extrapolation, while yielding a final accurate migration-velocity model evidenced by good quality and reliable depth images.
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