The Campos sedimentary basin is in the Rio de Janeiro State continental shelf between 21° and 23°S lat. The first oil field, Garoupa, was discovered in 1974 when Petrobras was drilling its ninth offshore wildcat. Since then, 10 more significant accumulations have been discovered and are in the delimitation or early development phase. Geologic interpretations suggest that at least four fields may have a reserve (volume of proven recoverable oil) of about 100 million bbl of oil. However, at this time, the 20 sq km area of the Namorado oil field alone is calculated to contain reserves of 250 million bbl.

The Namorado field was discovered in 1975, when Petrobras was drilling the wildcat 1-RJS-19 (22°27^primeSlat., 40°25^primeW long.) in a water depth of 166 m. The location was selected based on seismic interpretation of a structural high at the top of the Macae Formation (Albian limestones). At a depth of 2,980 to 3,080 m the well penetrated thick oil-bearing sandstones near the previously mapped horizon. Production testing flowed 6,000 bbl from the highly porous (30%) and permeable (more than 1 darcy) reservoir.

According to sedimentologic studies of ditch samples and cores, the reservoirs are marine turbidite deposits related to the first important transgression over the Albian limestone shelf.

The field was entirely delimitated using five extension wells and seismic interpretation based mostly on acoustic impedance seismic logs. The reservoir was named the Namorado Sandstone and appears to have formed by the coalescence of channels and lobes deposited over an irregular depositional surface. At the time of deposition, the area of the present oil field was a relative low where the turbidites were trapped.

As a consequence of structural activity related to salt flow in the Late Cretaceous, there was an inversion of relief. The reservoir now is located in an elongate, dome shaped, partly faulted structural high. Differential compaction over the structure enhanced the positive relief. The Namorado field accumulation is controlled both by structure and stratigraphy.