Angle Gathers from a Kirchhoff Pre-Stack Depth Migration using a Space-Lag Extended Imaging Condition

Abstract

Summary Traditional Kirchhoff pre-stack depth migration methods output surface offset common image gathers (CIG) but exploration workflows require subsurface reflection angle CIGs to extract accurate angle versus amplitude measurements. Providing any incremental uplift to the amplitude versus angle (AVA) attributes and the associated seismic inversions can significantly impact exploration and development success. Several high-end imaging techniques exist to extract subsurface angles directly, notably reverse time migration methods and common reflection angle migrations. Here, we explore the ability of the relatively cheap well-used Kirchhoff pre-stack depth migration to output subsurface reflection angle common image gathers via a local space-shift extended imaging condition. A layered synthetic model and a complex 2-D synthetic model are used to assess the space-shift image gathers output from such a migration scheme and to evaluate the seismic attributes relative to the traditional surface offset CIGs. The synthetic results show that the extended imaging condition clearly provides an uplift in the measured AVA over the surface offset migration. Finally, we show an example of a 3D space-lag gather from deep marine data and compare the resultant angle gathers with those generated from an offset migration and a time-shift imaging condition Kirchhoff migration.