Evolução tectono-sedimentar e sistema petrolífero de uma nova fronteira exploratória na margem equatorial brasileira.

Abstract

The Brazilian Equatorial Margin (BEM) evolved in response to transform motion between Brazil and Africa. The Mundaú sub-basin, Ceará basin, is an oil and gas producing region with four fields in shallow waters (Xaréu, Atum, Espada e Curimã). Besides that, in 2012, Petrobras drilled the Pecém well recording the first deep water oil discovery in the Mundaú sub-basin. This work aims at: Recognizing the 3D geometry and spatial distribution of faults in an area that includes the Curimã field and part of Espada field; Understanding the petroleum plays in shallow waters of Mundaú sub-basin; Extending the interpretations to the deep waters; Investigating the structural and sedimentary evolution and; Characterizing petroleum systems in this new exploration frontier. For such purpose, we used 3D and 2D post-stack seismic reflection, well data and geochemical data. Different tectonic domains were interpreted: proximal, distal and Romanche Fracture Zone domains. The proximal domain in shallow waters is characterized by planar to listric basinward-dipping faults that formed multiple half-grabens and displayed some transtensional movements. Hydrocarbons were found in footwall and hanging wall distributed in stratigraphic, structural and combined plays. In the distal domain, the petroleum play is combined. The entrapment of hydrocarbons discovered by the Pecém well was related to a normal fault and a deposition of the Ubarana shales (seal) above an angular unconformity caused by an erosion of the upper part of Paracuru Fm. This formation presented the main reservoir intervals which consisted of ~1 m thick intercalations of sandstone between shales, siltstones and marls. About the source rocks, the Mundaú and Paracuru formations are mature within the oil window, while the Ubarana Formation is considered immature. This work concludes that the Paracuru Formation is the main source and reservoir in the deep-water Mundaú sub-basin, constituting the Paracuru-Paracuru petroleum system. The results in this work have significant implications on petroleum exploration by proposing a developed transitional petroleum system in the distal parts of the BEM.