Tomographic Model Building with Angle Gathers

Tomograhic model building has commonly been conducted by using offset gathers from the prestack migration. However, in complex media, common offset images may yield an inconsistent image of the subsurface and thus cause problems in the model building process. The angle domain common image gathers (ADCIGs), on the other hand, do not suffer from such inconsistency and open a new opportunity for model building. The same model updating steps in the offset domain can be followed in angle domain with a different picking tool and a slightly different equation set up procedure. The residual picking is done robustly and efficiently using a single parameter curvature analysis. The angle gather ray tracing is more efficient than offset gather ray tracing. The method can be applied to angle gathers from ray-based or wave equation imaging. The field data test shows that this new work flow can provide a model that improves the base of salt and images below the salt.