The Campos basin is located offshore the State of Rio de Janeiro, between parallels 21 and 23°S. In 1974, while drilling the ninth wildcat in the basin, Petrobras discovered the Garoupa oil field. This field was the first in a new and important oil province in one of the little explored Atlantic-type basins. Between 1974 and 1978, 10 other significant oil discoveries have been made, but most of these new fields are still in the process of either delimitation or early development. At present only the 20-sq km Namorado oil field has proved reserves (recoverable oil volume) of 250 million bbl.

The Namorado oil field was discovered in 1975 by the 1-RJS-19 wildcat (22°27^primeS, 40°25^primeW) in 166 m of water. The prospect was located on a seismic structural high associated with an amplitude anomaly at the level of the Macae Formation (Albian carbonate rocks). In the interval between 2,980 and 3,080 m, the wildcat penetrated thick, oil-bearing sandstones interbedded with calcilutites in the upper part of the Macae Formation. In this well, an oil flow of about 6,000 bbl/day from the high-porosity (30%) and high-permeability (1 darcy) sandstone was estimated.

From sedimentologic analysis, the reservoirs were classified as deep-water marine deposits (turbidites) associated with the first major transgression over the Albian carbonate shelf. From this model, the first assumption was of variable sand distribution and strong stratigraphic control of the oil accumulation, which is now confirmed.

Today, six wells have been drilled in the field, some of them located by detailed interpretation of specially processed seismic data, such as synthetic acoustic impedance sections. This method proved to be very useful and accurate in mapping reservoir extension.

The reservoir rock, the Namorado Sandstone, was the result of coalescent deep-water channels and fans over a rough depositional surface when the area was a relative low containing several turbidite layers. In some places, there are continuous clean sandstone bodies 100 m thick. As a result of active faulting during the Late Cretaceous and because of different compaction over the reservoir, the relative low became an elongate dome-shaped high, partly limited by faults.

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