Dirty Salt Tomography Using RTM 3D Angle Gathers

Reverse Time Migration (RTM) 3D angle gathers can be an effective tool for the inversion of dirty salt velocities. Compared to the reflectivity-based inversion approach (Dirty Salt Velocity Inversion, or DSVI), the differences are twofold. First, DSVI detects dirty salt and performs velocity inversion using only reflectivity. DSVI’s reliance on reflectivity yields inaccurate dirty salt velocities when faced with density variations among intra-salt inclusions. Conversely, tomographic inversion based on 3D angle gathers uses residual curvature analysis of intra-salt reflectors and the regional base of salt seismic events, making it more reliable. Second, DSVI assumes that sediment inclusions have slower velocities than salt, whereas the angle gather domain tomographic inversion can invert both slow and fast velocities. Using synthetic and real data examples, we showcase this ability and demonstrate that angle gather domain tomographic inversion is a superior tool for velocity update when both slow and fast intra-salt inclusions are encountered.