Mineralogical Modeling and Petrophysical Properties of the Barra Velha Formation, Santos Basin, Brazil

The Santos Basin, offshore Brazil, has the most significant petroleum carbonate reservoir province in South America. The presalt carbonates reservoirs of the Barra Velha Formation (BVF) present a complex mineralogic distribution and heterogeneous physical properties, making it challenging to construct a reliable mineralogical model. Understanding rock mineralogy is important to petroleum prospects and the study of porous media, besides calibrating seismic facies. In this paper, we present a mineralogical inversion procedure to model reservoir and nonreservoir intervals within the BVF in a presalt field applying multicomponent inversion. The uppermost 15 to 28 m of the BVF, known as “Lula Fingers,” present higher values of gamma ray when compared with deeper intervals and are characterized by high modeled dolomite contents. Below the Lula Fingers region, the Upper BVF can be divided into BVF100 (top), which is characterized by low gamma ray values just above the BVF200 (bottom). They are formed mainly by shrub and spherulite-rich in-situ facies with fewer clay and Mg-clays contents, which are often replaced by dolomite and quartz. The bottom part of Upper BVF (BVF200) presents a microporous Mg-clay-rich interval, mainly in the structural flanks region, or a macroporous Mg-clay-poor interval, mainly in high levels. The present model fits well with the stratigraphic interval and allows a better understanding of the mineralogical distribution over the entire BVF100 and BVF200, particularly the lateral mineralogical variability in regions with structural highs and flanks.