Evaluation of fine-grains in pre-salt reservoirs

Pre-salt carbonates of the Santos Basin represent many challenges in the characterization of their reservoirs. This paper proposes the reservoir characterization of the Barra Velha and Itapema Formations based on the analysis of geophysical well logs, highlighting the influence of fine-grains presence. In the analyzed well, the results show that the Itapema and Barra Velha Formations are the exploratory targets in the Buzios Field. The Itapema Fm is less influenced by the occurrence of fine-grains, and presents better permo-porous characteristics than in the Barra Velha Fm. The presence of fine-grains causes a great negative impact on the Barra Velha Fm reservoir, affecting substantially the response of the well logs and compromising the reservoir quality. Due to this behavior, we propose the Barra Velha Fm sag phase division into Lower Sag and Upper Sag. This division is grounded at the end of fine-grain deposition. In its turn, the intra-Alagoas unconformity which separates the Upper Rift phase from the Sag phase, in the well logs, was correlated with the beginning of fine-grains deposition.