Análise petrofísica dos reservatórios carbonáticos da Formação Barra Velha (Pré-sal da Bacia de Santos) e comparação com calcários microbiais análogos

Abstract

This thesis presents the analysis of the petrophysical properties of the Pre-salt microbial carbonate reservoirs in the Santos Basin and microbial limestones obtained from several outcrops, with the main goal of identifying possible analogues with permo-porous conditions similar to rocks from the Barra Velha Formation. For this study, wells 1-BRSA-369A-RJS and 3-BRSA-496-RJS were selected, both located in the Lula field, as they have a complete suite of well data and have continuous logging at thicknesses greater than 200 m within the Barra Velha Formation. Among the outcrop samples, five lacustrine limestones formed in situ were studied: Lagoa Salgada stromatolites (Rio de Janeiro), stromatolite from the Yacoraite Formation (Salta Basin, Argentina), laminated limestone belongs to the Crato Member (Araripe Basin), Italian travertines from Tívoli region and tufas from the Bonito region (Mato Grosso do Sul). The results indicate that the travertines, characterized by crystalline framework and vugular pores, show permo-porous conditions similar to those found in reservoir rocks of the Barra Velha Formation, these characterized by vugular stromatolite limestones with moderate to good porosity, moderate and eventually high permeabilities, pore network formed by macropores and rare micropores. The Yacoraite stromatolite and the Crato laminated limestone have permo-porous characteristics that are similar to the non-reservoir zones, formed by laminated stromatolitic-spherulitic limestones with rare vugular pores, good porosity, low permeabilities, pore network formed by mesopores and micropores and low percentage of macropores. The Lagoa Salgada stromatolite and the quaternary tufas of the Bonito region (Mato Grosso do Sul) showed extremely high porosities and porous system formed by abundant micropores and macropores that resulted in extremely heterogeneous permeabilities that do not resemble the permo-porous conditions found in Barra Velha limestones in the Lula field. The conclusions of this work suggest that the Italian travertines from Tívoli, the stromatolite from the Salta Basin and the laminated limestones from the Crato Member may be possible analogs to the non-reworked limestones from the Barra Velha Formation from the perspective of reservoir petrophysics. The application of these analogues can be extremely useful in cases where there is no availability of samples and in understanding the lateral variations of facies and their petrophysical properties along the reservoir, especially in heterogeneous and complex conditions such as those found in the pre-salt.