ABSTRACT As the operator of several exploratory blocks in ultradeep waters, Petrobras was responsible for many presalt oil discoveries in Santos Basin such as Tupi, Carioca, Guará, and Iara. In partnership with the National Petroleum, Natural Gas and Biofuels Agency (ANP), Petrobras drilled well 2-ANP-2A, which resulted in the Libra discovery. In 2013, Libra was offered in the first bidding round executed by the Brazilian government under the new Production Sharing Contract for presalt areas. The winning consortium is comprised of Petrobras (operator), Shell, Total, CNOOC (China National Offshore Oil Corporation), CNPC (China National Petroleum Corporation), and PPSA (Pré-Sal Petróleo S.A.). The Libra discovery is sitting over a structural trap of about 550 km 2 (212 mi 2 ) closure at the Aptian top reservoirs level presenting a maximum oil column that can reach up to 900 m (2953 ft). The main reservoirs are lacustrine carbonates, deposited from the Neobarremian until the Aptian. Preliminary estimates indicate a volume of oil in place between 8 and 12 billion BOE. The development proposed for Libra started with Phase 0, in 2014, and is focused on information gathering, including appraisal wells, extended well tests (EWT), early production systems (EPS), and a pilot project. Phase 1 encompasses the definitive production systems and is expected to start in 2022 and finish in 2030.

Abstract The Campos Basin is one of the sedimentary basins on the Brazilian continental margin, located offshore of the State of Rio de [anciroIfiigure 1). The basin has an area of 100,000 km-, with its eastern limit in the oceanat 3000 m water depth with only 500 km2 onshore. Its structural limits are the Vitoria structural high to the north, Cabo Frio structural high to the south, and Campos fault (hinge line) to the west (bounding only on Cretaceous rocks). To the east, the basin theoretically extends to great salt diapirs (of Permian age) presently located between 3500 and 4000 m of water depth. The Campos Basin originated in the Lower Cretaceousbreak-up of Gondwana, as part of a rift valley system(Guardado et al., 1988). Stratigraphy of the basin is subdivided, from bottom to top, into the following formations:Cabiunas, Lagoa Feia, Macae, Campos and Embore. This lithostratigraphic sequence reflects its tectonicevolution and is more than 4 km thick. The LagoaFeia Formation lies unconformably over the volcanicrocks of the Cabiunas Formation (Figure 2), dated by KArmethods as between 125 and 130 m.y. The Lagoa Feia. Formation is the oldest sedimentary sequence of the basin and was deposited as a rift-related alluvial-lacustrinecomplex. At the upper part of the formation, there are thick molluscan shell deposits, known as the Coquinas sequence, which are important oil reservoirs int he Campos Basin, and are the object of the present study. This study was based on the analysis of core and cuttings of over 100 wells drilled in