Imaging Deep Water Salt Bodies in West Africa

The deep offshore of the Gulf of Guinea is a major challenge to seismic processing and imaging techniques, due to the complexity of the salt body structures (figure 1). Even though Kirchhoff prestack time migration (preSTM) can image the top of salt and the wider, simple sedimentary basin reflections, it fails elsewhere.

Strong surface related & interbed multiples and mode conversions at the top of salt are difficult to identify and eliminate, which makes stacking velocity or tomography inversion for sediment velocities difficult. The geometry of the salt bodies makes time processing assumptions a priori invalid.

Using synthetic elastic finite difference (FD) modeled data (Levander 1988, Don Larson, pers. comm.) we show that compared to Kirchhoff 3D preSDM, wave equation 3D PreSDM is necessary to properly image target sedimentary reflectors in between and below salt domes. However, this is true only for synthetic data using an exact model. In practice, the difficulty of deriving a proper model of sediment velocities drastically reduces the difference between the two algorithms.