ICE 2022


Oil recovery in carbonate reservoirs is complex because of their high petrophysical and geological heterogeneities, chemical reactivity and physicochemical interactions into the porous media during the fluids flow. Understanding microbialitic reservoirs from Campos Basin in the Brazilian Pre-salt is limited, so petrophysical analogs are commonly used. This work focuses on the pore characterization of pre-salt microbialitic carbonates analogs using travertines from the Tivoli area, that have abundant laterally continuous shrub-like fabrics, primarily in horizontal layers with progradation and aggradation stacking patterns, such as microbialites. Petrographic analyses allowed the identification of shrub morphotypes such as narrow dendritic and poorly developed pustular structures. Besides that, there is an abundant presence of peloidal micritic aggregates in spar calcite. Moldic porosity formed by the decomposition of reeds was observed. The mold of these structures serves as a substrate for the crystallization of shrubs. A large part of the moldic pores is filled with equant and dogtooth spar. Shrubs usually reflect specific microenvironments controlled by rates of water flow, evaporation, and microbial activity. Narrow dendriform morphologies occur in moderate/low energy flows, showing faster runoff conditions. Slow flow is more conducive for pustular types, being strongly influenced by evaporation. From computed tomography of vertical and horizontal plugs from two travertine blocks, it was observed the lateral continuity of the samples porosity, generated by the dissolution of structures that extend horizontally. In contrast, in vertical direction, the samples characterize themselves by higher matrix density, which leads to low vertical porosity. Pores with volumes from 0,002 to 355,159 mm3, with radii ranging from 0,078 to 4393,17 mm and shape factors from 0,398 to 17,9 were also featured. The analysis developed in this work showed that Tivoli travertine has a pore fabric formed by the dissolution of structures and empty spaces created by the microbial activity and carbonate precipitation, with extensive horizontal inter-pore connectivity, such as fractures with dissolution. That shows that travertine is a challenging rock given its high reactivity, creating many holes, which can lead to difficulties in preparing samples for specific studies, but, at the same time, configuring itself as an excellent analog to microbialites from the Brazilian pre-salt.