Seismic migration assessment of scenarios with locally varying basal anhydrite distribution in the pre-salt Brazilian fields

This study investigates the impact of basal anhydrite variability in the lower salt section of the Santos Basin, in Brazil, through seismic modelling of geological scenarios. Using 2D full-wave equation modelling, we simulated various geological configurations based on well data to evaluate the effects of vertical and lateral resolution, fault displacement, overburden influence, and basal anhydrite slope on seismic imaging. The results demonstrate that typical thin basal anhydrite layers – such as those with a thickness of c . 10 m – fall below the limits of vertical seismic resolution. Similarly, other configurations of anhydrite within the basal 50 m of the salt package are not reliably resolved, potentially leading to misinterpretation of the reservoir top. However, integrated analysis of seismic thickness and amplitude has proven effective in reducing interpretational discrepancies and enhancing reservoir characterization. The findings underscore the significant influence of overburden and lateral heterogeneities on seismic responses, reinforcing the need to incorporate detailed geological elements in seismic modelling. This approach contributes to reducing uncertainty in reservoir assessment and supports more effective well placement and drilling decisions in pre-salt exploration.