Roncador oil field was discovered by the I-RJS436A wildcat drilled on October 1996. It is located in the northern part of Campos basin, 130 km off the coast, in a 1.845 m water depth. Prior to the Roncador field Qscovery the northern area of the basin presented low exploratory interest because four dry wildcats had been drilled in the area without oil or gas shows, except for the Frade oil field which presents oil accumulation in Oligocene and Miocene turbidite sandstones. Based on a seismic amplitude anomaly an Upper Cretaceous reservoir thickness of 70 m was predicted, but a total net pay of 153 m was confirmed by the 1-RJS436A wildcat, divided into five main zones, interbeded with shales. Only the uppermost reservoir zone presents seismic amplitude anomaly and can be detected on seismic profiles. The other four reservoirs do not present acoustic impedance contrast with interbeded shales. Due to the seismic response variation of the reservoir, the oil field was divided into five confidence interval areas, which were important in constructing oil net isolith maps in order to evaluate in situ oil volumes. A new wildcat (1-RJS-513). aiming Tertiary turbidite sands as main objectives, also tested the southwestern area of the field and indicated a thick reservoir (60 m) even close to the pinch-out area of the field, although presenting a different oil quality than the 1-RJS436A wildcat. Actual in situ oil volume of 1,540.60 × 106 m3 and a recovery oil volume of 2,906.09 × l06 bbl is now being predicted, including the 1-RJS-513 well data.
Campos basin is located in the southeastern coast of Brazil and it covers an area of about 100,000 km2 from the coast to the 3.400 m isobath. It is separated from Espirito Santo basin by the Vitoria high to the north and from Santos basin by the Cabo Frio high to the south (Fig.1). Prior to the Roncador oil field Qscovery by 1-RJS-436A wildcat (drilled on October 1996. in a 1.845m water depth) the northern area of Campos basin presented low interest due to the exploratory response of the area (four dry wells and only one exploratory success in the area the Frade oil field). TW; main controlling factors were considered for the 1-RJS- 436A location proposal: reservoir distribution associated with intense salt movement and hydrocarbon migration pattern. Upper Cretaceous (Maastrichtian) reservoirs were drilled by 1-RJS436A well predcted by 2-D seismic survey and confirmed prior to drilling by 3-D seismic survey then available. A total reservoir thickness of 70 m was originally predicted based on seismic amplitude anomaly, but a total net pay of 153 m was confirmed by the 1-RJS436A wildcat, Qvided into five main zones interbeded with shales. Only the uppermost reservoir zone presents seismic amplitude anomaly and can be detected on seismic profiles. The other four reservoirs do not present acoustic impedance contrast with interbeded shales. Due to seismic response variation of the reservoir, the oil field was divided into five confidence interval areas, which were important in constructing a total oil net isolith map in order to evaluate the in situ oil volume (900.00 × l06 m3) and a recovery oil volume (1,412.00 × l06 bbl) distributed in an area of 130 km2.
