Reverse time migration of internal multiples for subsalt imaging

Abstract

Internal multiple reflections have different propagation paths than primary reflections and surface-related multiples; thus, they can complement illumination where other waves are unavailable. Consequently, migration of internal multiples may provide vital images in the shadow zone of primary reflections. We have developed an approach to image structures with internal multiples. With this method, internal multiples can be separated and used as data for reverse time migration. Instead of applying the imaging condition directly to the source and receiver wavefields, we decomposed the extrapolated source and receiver waves into up- and downgoing waves. Then we applied the imaging condition to upgoing source and receiver waves to form an up-up (UU) image and also to downgoing source and receiver waves to form a down-down (DD) image. The image of the true reflector and the artifacts behave differently in the DD and UU images. A similarity analysis is conducted to the UU and DD images to separate true images from artifacts. Numerical examples with simple velocity models are used to demonstrate how to construct UU and DD imaging conditions and eliminate migration artifacts. Finally, we test the 2D SMAART JV model with salt structures for migration using internal multiples.