Abstract

Recent exploration discoveries in the deep-waters of offshore French Guiana and Brazil's Ceará and Sergipe deep-water basins have tested the applicability of West Africa exploration analogs to exploration concepts for the Atlantic Equatorial Margin of South America. These initial successes are encouraging, but the number and expanse of the numerous under-explored basins along Brazil's extensive coastline present significant challenges for optimized exploration programs.

Analysis of regional surveys using high-resolution multi-beam scanning and precision-guided piston coring of suspected seepage anomalies is proving to be a robust and cost-effective methodology for guiding regional exploration programs in a highly competitive exploration market. Such scanning and coring campaigns are providing key insights into the presence, type, and extent of petroleum systems in these under-explored frontier areas. The results of basin-wide surveys programs can not only confirm hydrocarbon generation and type, but also guide the optimized use of subsequent, more costly technologies, used to further identify and risk areas at the prospect level.

Multiple deep-water exploration play concepts are available in these under-explored frontier areas that have the same syn-rift lacustrine sediments, post-rift marine environments and turbidite reservoirs as recent discoveries. This paper examines these frontier basins, the likely play concepts present, and the prioritization of each with respect to exploration potential and hydrocarbon sourcing, as indicated by the physical presence of hydrocarbon seepage on the ocean floor.

Introduction

The Brazilian Equatorial Margin is a wide region located on North and Northeast of Brasil (Figure 1), encompassing about 344,000 km2 in shallow waters down to −250m and about 200,000 km2 in deeper waters from −250m to −3000m bathymetry.

The initial offshore exploration activities in the Brazilian Equatorial Margin began in 1970, and since then approximately 490 wells have been drilled in shallow water. The first oil discovery was the offshore Ubarana oil field in 1973, located in the Potiguar basin, and the first gas field was the Pirapema field in 1976, in the Foz do Amazonas Basin, which was abandoned as sub-commercial. From 1977 to 1979, Petrobrás made four small oil discoveries in the shallow water of Ceará Basin.

To-date, the deep-water region of the Equatorial Margin has been very lightly explored, with only about 20 deep-water wells being drilled, nine of which were abandoned due to mechanical problems. In 2012, Petrobrás made an important light oil discovery in deep-water Ceará Basin at the 1-CES-158-CE well in an apparent turbidite reservoir. However, most of the prospects drilled have tested structural traps targeting the Aptian and Albian reservoirs sourced by Aptian or older Lower Cretaceous rocks, which were also the main targets for onshore exploration activities in the Equatorial Margin.

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