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High Impact Exploration Inventory in an Emerging Hydrocarbon Province, Morandava Basin, Offshore Madagascar


Rifting of Madagascar from East Africa created a rich array of structural and stratigraphic traps in an area that has seen little sub-aerial erosion and extensive source rock deposition for more than 150 my. Recent gas discoveries on the conjugate Rovuma margin have ignited interest in the prospectivity of the Madagascan margin. Rovuma wells have targeted a range of plays from onshore extensional (Mecupa), thrusted Tertiary traps (Windjammer discovery), Cretaceous stratigraphic traps (Ironclad) and Tertiary slope channels and fans (Tubarao, Lagosta, and Barquentine discoveries). In contrast, no wells targeting equivalent plays have been drilled in any of the western Madagascar basins. Consequently, the deep offshore represents an entirely untested province despite the recent successes on the opposite margin. 2-D and 3-D data are used in this study with long distance 2-D well ties. As a frontier area for exploration, ages of the stratigraphy in the study area are largely unconstrained by well data. Interpretations were made primarily based upon the identification of seismic reflection terminations. Key geologic surfaces mapped were Top Jurassic Maximum flooding (MFS), Intra- Cretaceous Sequence Boundaries (SBs), Upper Cretaceous SB, Top Maastrichtian SB, Top Oligocene MFS, and Top Miocene MFS. Two main erosive surfaces were interpreted, the Top Jurassic unconformity and the Upper Cretaceous unconformity. Stratigraphic interpretation using a combination of Variance/Coherency and Spectral Decomposition were used to support structural culminations. The prospectivity of the offshore Madagascar study area is dominated by four-way dip closures at Cretaceous and Jurassic levels, Tertiary turbidite fans and slope channels, and possible Mesozoic reefs. Thermal model results as well as slick and seabed cores suggest possible oil prone source rocks that could be active in the offshore area. These range from Triassic through Lower Jurassic, Middle Jurassic, and Lower Cretaceous sequences. Similar Triassic source rocks are responsible for more than 20 billion barrels of exhumed hydrocarbons onshore Madagascar. The study area has significant source rock potential that is oil mature from Triassic through Jurassic with peak expulsion throughout the Miocene and Plio-Pleistocene.