Characterization of Barra Velha Reservoir-Non Reservoir Interfaces in a Pre-Salt Field in Santos Basin-Brazil Using Seismic AVO Modelling.

Abstract

Summary The Lower Cretaceous Barra Velha (BVE) unit is the main reservoir in our area of study, which consists of heterogeneous carbonates beneath a thick salt layer. Pre-Salt wells have shown that underneath the BVE reservoir, there could be several non-reservoir rocks (e.g., microporous carbonates, shales, volcanics) embedded in different formations that are hard to predict pre-drill. This poses a challenge, as BVE reservoir thickness and quality could be affected by a variety of underlying geological formations with distinct lithologies and facies. The Aptian BVE Formation consists of several hundred meters thick dolomitized limestones and shales. The mud-poor section is the main reservoir interval. The Itapema Fm. consists of thick (hundreds of meters) limestones (including coquinas) and organic rich shales. The Barremian Picarras Fm. is mostly made up of clastic and carbonate rocks, that contain conglomerates, with clasts of basalt and quartz and talc-stevensite shales. Finally, the lowermost and oldest Camboriu Fm. consists mainly of basalts. Despite efforts to understand the main factors driving the BVE reservoir elastic and seismic behavior for 3D and 4D interpretations and reservoir characterization, we still miss advanced geophysical analysis of the interfaces between different geological units that are important for quantitative seismic interpretation.