Paleogeography of the South Atlantic Salt Basin: Key to the Understanding of Hydrocarbon Systems Along the Continental Margins of the Angola, Congo Republic, Gabon, and Brazil

Phillip R. Smith¹, Kevin M. Bohacs², Wayne Gardiner¹, John Hohman¹, and Garry D. Karner^2
1Exploration, ExxonMobil, Houston Texas, TX
²ExxonMobil Upstream Research Company, Houston, TX

Exploration activities have focused on deepwater areas along the continental slope. With the high cost of seismic data and exploration drilling in deepwater, lowering play and prospect risk by using basin modeling has become important for deepwater exploration economics. Paleogeographic mapping has been used to determine play element distribution for both pre- and post-salt intervals, critical for developing a robust basin model.

Paleogeographic maps of source and reservoir distribution were constructed from calibrated seismic facies, well and outcrop data, and depositional environment modeling and quantitative basin analysis.

The South Atlantic salt basins form aA relatively wide continental margin underlain by rifted and attenuated continental crust and possibly exhumed lower crust and continental mantle. is interpreted along the South Atlantic salt basins. Thick synrift sediments were deposited in grabens that locally contain rich, lacustrine source rocks along with good clastic and carbonate reservoirs.

Thick , widespread salt was deposited during marine incursion and subsequent restriction of the initial basins duringin the Aptian. The salt was deposited on a relatively low-reliefgentle surface unlike the previous higher relief, rifted terrain. The local slope of the presalt surface, underlying overlying rigid basement highs and compactable thick synrift sediments, played a subsequent roles in structural deformation as the continental margin was loaded by younger sediments.

Abundant structuring, the stacked nature of both reservoir and source units, areas of super seals (evaporites and organic rich shale) or areas of active hydrocarbon generation, has provided for an effective hydrocarbon system. Understanding these play elements has resulted in a (historical exploration success ratio of greater than >30%).

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery