PrestackSeparate

Prestack phase-shift migration of separate offsets in laterally inhomogeneous media

Using the stationary-phase method, prestack phase-shift migration is implemented one offset at a time. This separate-offset implementation allows for a Fourier (reasonably fast) wave-equation type migration on data with irregular offset sampling. However, the separate-offset phase-shift migration, like its zero-offset counterpart, handles only vertically inhomogeneous media. Using the combination of the split-step and the phase-shift-plus-interpolation (PSPI) approaches, the separate-offset phase-shift migration is extended to handle laterally inhomogeneous media. The cost of the separate offset implementation is practically equivalent to that of the conventional zero-offset version. However, due to the lack of exact source and receiver ray trajectory information in the separate-offset implementation the Split-step and PSPI handles only smooth lateral inhomogeneity. Specifically, it produces images equivalent to those resulting from smoothing the velocity model laterally over a window equal to the half offset. Thus, for zero-offset or laterally homogeneous media the separate offset migration is equivalent to any wave-equation based migration. For finite-offset data in laterally inhomogeneous media errors may occur. Such errors depend primarily on the strength of lateral inhomogeneity.

Using this separate-offset phase-shift migration, we obtain accurate images of synthetic data of a model with large reflector dips and good images from real data from offshore Trinidad.

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Department of Physical Science and Engineering 4700 King Abdullah University of Science and Technology

Thuwal 23955-6900 Saudi Arabia