Equivalent offset migration in anisotropic media

Pavan Elapavuluri and John C. Bancroft

ABSTRACT

Equivalent offset time migration has been shown to be a very effective migration technique. In its simplest form, this method assumes that the source/receiver traveltimes, or prestack diffraction shape of a scatterpoint, is defined by the double square-root (DSR) equation. The DSR equation usually assumes a hyperbolic definition of the source and receiver ray times based on the root-mean-squared (RMS) velocities. The equivalent offset is then defined by equating the DSR equation to a hyperbolic equation in which the offset is defined to be the equivalent offset. This method is fast and yields accurate velocities.

Applications of the equivalent offset (EO) method to anisotropic media have involved depth migration techniques to define the source/receiver traveltimes that are equated to a hyperbolic equation that (again) contains the equivalent offset. Using the equivalent offset to sort data in a migration gather aids in the velocity analysis process. This method does not have a speed advantage as it requires traveltime computations of a typical depth migration.

Our objective is to combine anisotropic traveltime estimates into the DSR equation with EO time migration for more accurate imaging at fast computational speed.

This technique was first tested on a simple anisotropic numerical model and then on a data set acquired over physical anisotropic model. An advantage of this method is that we can migrate data without the explicit information of anisotropy parameters.

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