Exploration Opportunities in the Pre-Salt Play, Deepwater Campos Basin, Brazil

The discovery of the Lula Field by Petrobras and partners in 2006 opened a new E&P frontier in Brazil, the Barremian/Aptian pre-salt play in the offshore Santos and Campos basins. Several multi-billion-barrels discoveries have been made in carbonate reservoirs in the pre-salt sequences of these two producing Brazilian basins and their African counterparts. These recent Santos and Campos basin discoveries, after appraisal, are expected to add at least 10 Bboe to Brazilian proved reserves by 2022 (from ANP, 2014). The Brazilian pre-salt play consists of rift/sag-sourced oils, accumulated in Aptian reservoirs (microbialites) in structural closures or paleo-topographic/depositional highs just beneath the salt (Figure 1). The overlying Aptian evaporites provide the sealing unit. In addition to the microbialites, deeper coquina reservoirs have become important exploration targets in the pre-salt succession of Campos and Santos basins as proven by successful well tests on the Búzios (previously referred to as Franco) and Libra pre-salt discoveries. Based on available Santos Basin well data, observed seismic responses, as well as in published analytical studies of the major commercial and non-commercial pre-salt discoveries in Brazil (e.g. Fontes and Zalan, 2014 and Petersohn et.al., 2013), two main reservoir targets are recognized for the pre-salt within the study areas: a. late rift coquinas: lacustrine facies deposited at the Late Barremian to Early Aptian and, b. the younger rift/sag microbial limestones or microbialites: mostly lacustrine units deposited during the Aptian just before the establishment of the major evaporitic sag basin between South America and Africa. Microbial limestones are currently the major producing reservoir units for the pre-salt play in both Campos and Santos basins. The microbialites that occur just beneath the base salt can be interpreted as “organosedimentary deposits that have accreted as a result of a benthic microbial community trapping and binding detrital sediment and/ or forming the locus of mineral precipitation” (Burne and Moore, 1987, pp. 241–242). Microbialites formed in large, mostly lacustrine, settings due to the activity of extremophilic micro-organisms surviving in potential hypersaline and hydrothermal conditions during the Aptian thermal sag phase that followed the syn-rift deposition.