Abstract: Campos and Espírito Santo Basins - Albian to Maastrichtian Evolution and Reservoir Distribution in Proximal Areas

Rangel, H. D.; C. V. Tagliari; S. G. Oreiro*; M. F. B. Moraes; and J. R. Brandão - Petrobras/E&P

Albian to Maastrichtian structural evolution and reservoir facies distribution in proximal areas at both Campos and Espírito Santo basins were associated with Aptian salt movement, and although salt was thinner in proximal areas of both basins it controlled the architecture of lower Albian structural highs, composed of both shallow water siliciclastic and carbonate rocks. Rafting of Albian structures created adjacent structural lows from Cenomanian to Maastrichtian, site of thick deep water shales and turbidite sandstones, which contain important oil accumulations in deeper water areas. Such model constitutes an important exploratory frontier in the proximal area of Campos basin. Rafting evolution lasted longer in Campos Basin than in Espírito Santo Basin due to lower sediment input in Campos Basin during early Albian.

Espírito Santo basin proximal section is different from the one found in Campos basin because rafting occurred mainly during early Albian associated with intense sediment arrival in the area. Cenomanian to Maastrichtian section is rather thinner due to less salt movement during this time, although rafting becomes gradually more intense and affects younger section in deeper areas, Upper Cretaceous sediments are thinner in the proximal area, except inside Fazenda Cedro and Regência paleocanyons, located respectively in the northern and southern part of the basin. Both paleocanyons contains upper Cretaceous turbidite reservoirs within them, and Fazenda Cedro paleocanyon contains four oil fields in Maastrichtian reservoirs. Adjacent to the northern border of Regência paleocanyon, in the downthrown block of the hinge line, there are small oil accumulations in lower Albian calcarenites and Cenomanian reworked carbonates . Main reservoirs of the oil accumulations in this area are lower Albian siliciclastic rocks deposited in a transitional environment, varying from fluvial to shallow marine. The siliciclastic rocks are interbeded with shallow water carbonates, indicating sedimentary ciclicity of the environment.

In Campos basin lower Albian structural features are also smaller in size than in the intermediate and distal areas of the basin, but the height of them can reach 500m in thickness. Vertical facies distribution in these structural features are coarse siliciclastics which were capped by high energy carbonates, indicating a drowning of the environment in the final stages of lower Albian deposition. Lower Albian high energy carbonates were covered by upper Albian and Cenomanian calcilutites and marls. Lower Albian siliciclastic sediments were deposited as sand foreshore and upper shoreface bars with maximum porosity of 25% and maximum permeability of 1,370 milidarcy. Because less-developed Cenomanian and upper Cretaceous turbidite sandstones were sampled only over lower Albian structural highs they generally present less favorable permo-porosity values because they occur as thinner layers. In Campos basin upper Cretaceous sediments were covered by Paleocene and lower Eocene slope shales and turbidites. Shallow water platform sandstones and carbonates were established during mid Eocene in both Campos and Espirito Santo basins.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil