Abstract

Búzios, discovered in 2010, is a supergiant pre-salt field, located in the Santos Basin. The main reservoirs are lacustrine carbonates, deposited from the Barremian until the Aptian. Preliminary estimates indicate a volume of oil in place (OIP) on the order of 29,900 MMBOE, thereby ranking it as the largest of the pre-salt fields. The understanding of pre-salt reservoirs continues to be a challenge because of complex facies distributions and tectono-stratigraphy. This study focuses on describing the tectono-stratigraphic framework of Búzios Field, using criteria from 3-D seismic, well log, and core data. Three-dimensional seismic interpretation reveals the Búzios’ rift configuration as a series of horst, graben, and half-graben structures, which are highly faulted (N30W–N30E) because of a complex transfer zone interpreted in the area. Based on seismic interpretation, the rift section was subdivided into a lower and upper rift section. The lower rift section was strongly affected by normal faults, whereas the upper rift was exposed to a less expressive faulting process and has a thinner sedimentary wedge. The upper section corresponds to a commonly observed coquina interval (the Itapema Formation), which serves as the lower pre-salt reservoir in the Búzios Field. Lastly, prior to salt deposition, the post-rift mega-sequence (sag section) is comprised of the Barra Velha Formation, which is composed of biotic and abiotic carbonate reservoirs in a complex structural setting. Based on core analysis from the 3-BRSA-944A-RJS well, the most common facies in the Itapema Formation reservoirs are rudstone and grainstone, composed of bivalve shells, with an average porosity and permeability of 12.5% and 88.7 md, respectively. The Barra Velha Formation reservoirs consist of four main carbonate facies: spherulites (most common), crystal shrub, carbonate laminates, and rare stromatolites, which display an average porosity and permeability of 9.4% and 122.6 md, respectively.