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Regional Prospectivity of Offshore Namibia and the Angolan Namibe Basin

Abstract

The deepwater basins of Namibia and Angola hold tremendous hydrocarbon potential. These frontier areas of West Africa have seen a huge demand for high quality, detailed and innovative seismic data which can be set in a regional context, in order to assist in the exploration, understanding and de-risking of these potentially prolific hydrocarbon provinces. Offshore Namibia and the Namibe Basin have similar geological histories, controlled largely by the opening of the South Atlantic in the Early Cretaceous. The volcanic Walvis Ridge separates the two regions and influenced sedimentation to the north during rifting. The syn-rift stage of both areas is typified by a series of asymmetrical horst and graben basins, in which thick sequences of fluvial-lacustrine sediments were deposited in narrow deep lakes. In analogous formations in the conjugate margins of South America, burial of algal blooms and plant detritus, along with anoxic bottom waters lead to the formation of high quality source rock. Reservoir rocks are typically conglomerates and sandstones deposited in fluvial and lacustrine environments shed locally from uplifted horst blocks. As active rifting ceased in the Early Cretaceous, the early post-rift, or sag phase was characterised by the deposition of sediment in continental, fluvial and transgressive lagoon environments. The Walvis Ridge controlled sedimentation to the north during this period; repeated cycles of marine incursions across the ridge into a restricted basin led to a thick evaporite sequence. Although this salt is widespread across West Africa it thins into the Namibe Basin and is absent from Namibia where open marine conditions prevailed earlier than to the north. 2–5 km of post-rift sediments overlay the syn-rift sections along this margin. In an effort to better understand these potential petroleum systems of offshore Namibia and the Angolan Namibe Basin, PGS, in association with Sonangol and Namcor, has recently acquired three 2D surveys using the GeoStreamer® dual-sensor broadband towed streamer system. This new PGS seismic data gives enhanced imaging of the features described above, improving the regional understanding of the tectonic evolution, structure and geology. These new insights, summarised in this paper, significantly increase prospectivity and de-risk exploration in the frontier Namibia and Angolan Namibe basins.