Pre-Salt Depth Imaging of Santos Basin, Brasil
Recent large pre-salt discoveries in deep water Santos Basin, Brasil, such as Tupi and Sugarloaf, prompt significant interest in better pre-salt imaging. Although the sedimentary velocity variation is relatively smooth, depth migration is required for imaging complex salt and pre-salt layers. The presence of both mobile salt and layered evaporates makes the velocity model building flow more challenging than the flow in the Gulf of Mexico (GOM). The main difference is that we introduce an additional step of salt layer velocity update. Together with advanced imaging algorithms such as RTM, this new flow can significantly improve the image of pre-salt structure. To further improve the pre-salt images, we may have to include anisotropy in the model building flow. Without a lot of publicly available well information in Santos Basin, it is difficult to determine the anisotropy level, but seismic data indicates that anisotropy does exist in this area. Ignoring the anisotropic effects can incorrectly position salt flanks and distort the base of salt (BOS) and pre-salt structures. Furthermore, the dip angles of some deep basins can reach more than 50 degrees. With such highly-dipping bedding, even vertical transverse isotropy (VTI) may be significantly inaccurate. TTI imaging may be needed.