Using RTM Angle Gathers for Velocity Model Building in a Structurally Complex Area - A Real Case Study

Velocity model building for pre-stack depth migration mainly relies on ray-based tomography methods. These methods usually produce good results when the moveout (RMO) information is reliable. From the imaging side, it is now established that Reverse Time Migration (RTM) is a higher fidelity imaging algorithm compared to Kirchhoff and Beam migrations and can provide the kinematic information needed for tomographic inversion. We show in this paper a real example of using RTM 3D angle gathers for ray-based tomography. The comparison between Kirchoff migrated and RTM migrated gathers shows the uplift of RTM on focusing and signal to noise ratio which in turn improves the RMO picking. We then show that nonlinear slope tomography can improve the velocity model and lead to better imaging provided the kinematic properties of the migration algorithm used are preserved during demigration of the RMO picks.