Ubarana is the first commercial oil field on the northern continental shelf of Brazil. Discovery well 1-RNS-3, drilled in 1973, was located on a seismic structural high in the offshore extension of the Potiguar basin, about 13 km from the coast and 160 km northwest of Natal. The well penetrated oil-bearing, fluvio-deltaic sandstones of the Cretaceous Acu Formtion. Five outpost wells, also located on the mapping of seismic horizons adjacent to the producing interval, helped to extend the limits of the accumulation. A total of 1.4 million cu m of oil has been produced between 1976 and October 1980.

The surface area of Ubarana field is about 35 sq km with oil-bearing reservoirs at an average depth of about 2,400 m. Permeability and porosity of the sandstones are generally poor. Pressure is normal and the main production mechanism is solution gas-drive. The volume of oil in place is about 37 million cu m; estimated recovery factor is 29%. There are presently four platforms in the Ubarana field active in drilling and production with 32 producing wells, and 14 locations to be drilled. Ubarana is not yet fully delimited because a recently drilled well, 3-UB-25, has shown that the field extends southward. This has resulted in selection of four additional production platforms which will allow drilling another 48 wells for production.

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