Abstract: An Outlook on the Petroleum Potential of the Brazilian Sedimentary Basins

Guardado, L. R. - Petrobras / E&P

Since its creation, in 1954, Petrobras has been facing the great challenge of exploring petroleum in a huge sedimentary area (6,400,000 km²) that comprises more than 30 basins. These basins, ranging in age from Proterozoic to Tertiary, represent a great variety of tectono-sedimentary settings and petroleum systems. Before the creation of Petrobras, only 162 exploratory shallow wells were drilled in Brazil, mostly in the Paleozoic intracratonic basins and in the Reconcavo rift basin, resulting in 10 discoveries. At the beginning, Petrobras focused its efforts in the large Paleozoic basins and in the onshore portions of the marginal basins, with commercial discoveries restricted to the later. In the late 60?s, the exploration was extended toward offshore. The succession of discoveries in the continental shelf, in the 70?s, highlighted the great potential of the Atlantic basins. With well established exploratory models, activities moved toward the deep waters, resulting in the discovery of the first deep-water giants in the middle 80?s. In this exploratory effort, it was invested more than 15 billion dollars (money of the day), resulting in the discovery of 22 billion barrels of total reserves (equivalent oil), from which more than 5 billions have been already produced. In order to obtain these results, more than 1,750,000 km of seismic were acquired and 4,715 exploratory wells were drilled.

The perspective for the future points out to an increase of the exploratory activity in the deep-water regions along the Brazilian margin. The encouraging results in the Sergipe-Alagoas Basin, with the recent discovery of oil with good quality in Cretaceous turbidites, and the discovery of a giant accumulation in Tertiary turbidites of the Santos Basin support this strategy. In addition, in the Campos Basin, the exploration is already moving to the ultra-deep waters. Deeply buried reservoirs are also important targets, both in the deep water settings and in exploratory mature areas. In the Campos Basin, the targets are the ?coquinas? deposited in intrabasinal rift highs. Rift siliciclastic reservoirs are also targets, mostly in the Santos, Reconcavo and Potiguar basins. The intensive utilization of 3D seismic in the onshore and shallow portions of marginal basins will enable the discoveries in the mature areas of the northeastern basins, where producing facilities are available. The search for gas is another challenge that Petrobras has been facing. Despite the complexity of geology in most of the gas prone provinces, good results have been obtained. In the Amazon, where a series of discoveries have been done since the 80?s, the expectation is to add significant new reserves. The recent first commercial discoveries in the Parana basin certainly will stimulate new investments for gas exploration in this Paleozoic basin. Tight sands of the rift section will also receive exploratory investments, because its potential and its location in areas with installed facilities. Gas hydrates constitute a new exploratory frontier offshore Brazil, and must be considered as a petroleum feedstock resource. Preliminary evaluations indicate great accumulations in the Pelotas and in the Foz do Amazonas basins, where typical gas hydrates features were already identified.

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