Tectono-sedimentary evolution and petroleum systems of the Mundaú subbasin: A new deep-water exploration frontier in equatorial Brazil

Abstract

The Brazilian equatorial margin (BEM) evolved in response to transform motion between Brazil and Africa. In 2012, Petrobras drilled the Pecem well in the Mundau subbasin (Ceara Basin) of the BEM to record the first deep-water oil discovery in the region. This work investigates the deep-water evolution of the Mundau subbasin focusing on its structural and sedimentary evolution, and characterizes the petroleum systems in this new exploration frontier. For such purposes, poststack seismic reflection, borehole, and geochemical data were used. Three tectono-stratigraphic sequences representing synrift (Mundau Formation), transitional (Paracuru Formation), and drift strata (Ubarana Formation) were divided into seven seismic units. Different tectonic domains were interpreted: proximal, distal, and Romanche Fracture Zone. Typical structures of transform margins, such as marginal ridges and marginal plateaus, were not identified in the Mundau subbasin. Instead, the subbasin was predominantly deformed by transtensional movements. The Mundau and Paracuru Formations are mature within the oil window, whereas the Ubarana Formation is immature. Main reservoir intervals consist of approximately 1-m (∼3.28-ft)-thick intercalations of sandstone between shales, siltstones, and marls. The seal rocks comprise shales in the Ubarana Formation, whereas the hydrocarbon trap is related to an unconformity and a normal fault. This work concludes that the Paracuru Formation is the main source and reservoir in the deep-water Mundau subbasin, effectively comprising a Paracuru–Paracuru petroleum system. The results have significant implications for petroleum exploration in the BEM by proposing a developed transitional petroleum system in the distal parts of northeastern Brazil.