- Copyright © 2003 Society of Exploration Geophysicists
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 and 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, we show that, compared to Kirchhoff 3D preSDM, wave equation 3D PreSDM more properly images 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.
To devise the best methodology for producing high quality images in this area, a model of appropriate complexity was built, including two salt bodies overlying narrow basins with turbiditic complexes (Figure 2). From this conceptual model, GX Technology created a set of synthetic data using elastic finite difference forward modeling.
A gridded model, representative of deepwater salt tectonic environments was used. This included density, VP, and VS grids. In order to represent gas hydrates near the seabed, very low S-wave velocities (180 m/s) were included. The lowest …