Geomechanical and Geopressure Modeling from Seismic Velocities in Pelotas Basin

Abstract

Most of the information available in frontier exploration areas comes from seismic data, eventually from legacy 2D seismic lines. This is the case of the Pelotas Basin, the southernmost basin along the Atlantic continental margin in Brazil. The basin belongs to the Austral sector of the rift and breakup of the Gondwana Supercon- tinent, in the Early Cretaceous. Significant hydrocarbon discoveries have been reported over the last few years in this sector, along the counterpart African margin, in ultra deep-water, offshore Namibia. This article describes a successfully tested workflow to forecast geomechanical and petroleum system information during seismic reprocessing of outdated 2D data from the Pelotas Basin. A geomechanical-geopressure model was produced from seismic velocities double-checked with both normal move out and image gathers. The model, which was computed with standard equations (eg. Gardner’s and Eaton’s), and conceptual velocity gradients of normal compaction trends, is fully consistent with the mechanical stratigraphy and deformation analysis of the studied area, close to the shelf border in the Central Pelotas Basin. The geomechanical results pertinent to petroleum systems indicated good seal potential and probably hydrocar- bon generation associated with an overpressure regime in the deeper Paleogene and Cretaceous successions of the basin, particularly beyond shelf border and slope. In this way, the Pelotas Basin may share, in deep-water environments, the same promising play found in recent times in Namibia.