Target-oriented common reflection angle migration

A 2-D and 3-D ray-based migration/inversion approach for the construction of common image gathers (CIG) in the reflection angle domain is presented. We show that amplitudes and phases of the reflected events are preserved for a wide range of angles even in complex areas with multi-arrivals. The method can be used for detailed velocity-model determination and for accurate amplitude variation with angle (AVA) analysis in such areas. Our method is a target-oriented approach, based on shooting rays from the image points up to the surface. The migration aperture and density of rays per solid dip angle at the image points is chosen with the condition that we obtain optimal reconstruction of the migrated events, avoiding migration operator aliasing. However, using the whole migration aperture might be very time consuming, especially for steep angles, which require small angle step increments. We therefore present an implementation of a model-driven aperture migration, which makes the migration feasible and relatively fast even for large-scale complex 3-D models. The migration aperture is defined from information about the local directivity of the main reflectors, obtained from interpreted horizons. The implementation of the method for complex geological structures is demonstrated with the 2-D Marmousi dataset and with the 3D SEG/EAGE salt model.