Searching for Potential Analogues for the Pre-Salt Santos Basin, Brazil: High-Resolution Stratigraphic Studies of Microbialite-Bearing Successions from Salta Basin, Argentina

Freire, Ednilson B.⁴; Terra, Gerson J.²; Raja Gabaglia, Guilherme ²; Lykawka, Ricardo ³; Rodrigues, Eduardo B.¹
(1)CENPES, Petrobras S.A., Rio de Janeiro, Brazil. (2) Petrobras University, Petrobras S.A., Rio de Janeiro, Brazil. (3) Reserves and Reservoirs, Petrobras S.A., Rio de Janeiro, Brazil. (4) Reservoir Caracterization, Petrobras S.A., Vitória, Brazil.

The Salta Basin (Province of Salta, Argentina) was developed from the early Cretaceous to the Eocene under a distentional regime. This tectonic setting enabled the development of a rift basin where accumulated the sediments of the Pirgua and Balbuena supersequences. The upper part of the Balbuena Supersequence is formed by the Yacoraite Formation (Upper Cretaceous to Lower Paleocene), which was formed during the first sag phase of the basin, and is characterized by microbialite-bearing sucessions and subordinate pelitic rocks. In the northeastern portion of the basin (Lomas de Olmedo Sub-Basin), these rocks are covered by an evaporite succession that characterizes the Olmedo Formation, deposited during the post-rift phase. This context is very similar to that where microbialite reservoirs accumulated in the Pre-Salt section of offshore Brazil. In the central part of the basin, there are outcrops of the Balbuena Supersequence where it is possible to describe a well-exposed cyclic sedimentation, enabling the discrimination of stratigraphic cycles in different scales and orders. The large number of outcrops in the area stimulated the development of a methodology for stratigraphic and diagenetic facies characterization of microbialite reservoirs. This study focuses the development of a methodology to characterize and understand the evolution of carbonate systems of microbial origin in the area, from the viewpoint of high-resolution sequence stratigraphy. Salta outcrops also allowed the establishment of a field school where the methodological bases of the research can be disseminated and applied in the characterization and 3D modeling of the pre-salt reservoirs from offshore Brazil. The research was based on the detailed description of the outcrops, photomosaics, petrographic studies, spectral gamma ray logs (Total, Th, U and K) measured directly in the outcrops, and geostatistical characterization of facies distribution. The characterization of high-resolution stratigraphic cycles and the measurement of parameters, such as the traceability coefficients of the main architectural elements from the Salta Basin microbialite successions, can be used as input for the production zoning, predictability of reservoir facies, and geocellular modeling of carbonate reservoirs of microbial origin from the Pre-Salt Santos Basin.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.