Subsalt seismic reservoir characterization, how to chase optimal results?

Subsalt seismic reservoir characterization remains a challenging topic due to the low imaging quality and geological heterogeneities. This paper takes a close look at a pre-salt carbonate field in the Santos basin, Brazil. We demonstrate the value of an integrated workflow to include different information from log to reservoir scales to deliver the best quality of seismic-derived impedance and porosity models. At log scale, to honor the seismic response at the base of salt (BOS), we suggest adding the lacking anhydrite layer below the BOS based on geological and drilling information. The proposed strategy appears to be a step change for the wavelet estimation and the inversion products. At field scale, to honor the complex and highly faulted structure, we suggest using a geological grid for prior model building. The combination of this strategy with joint-impedance-porosity process provides not only high quality Ip, but also good porosity magnitude at wells, at superior quality compared with the standard two-step porosity estimation (Inversion followed by porosity estimation). To mitigate the uncertainty in the seismic imaging process, we suggest using RTM as reference data for quantitative inversion products, while Kirchhoff can be used for qualitative interpretation, especially for thin bed detection and identification.