West Africa Pre-salt Exploration: Background and Perspective of the West African “Tupi” Myth
The deep water pre-salt trend in the entire South Atlantic rift basin is in the exploration spotlight since the giant discoveries made in 2006 in the Santos Basin (Brazil). Academia and industry are devoting increasing attention and resources to the syn-rift and sag sequences pre-dating the widespread deposition of evaporites (110-120 m.y.); special focus is on the relationships between the two sides of the South Atlantic with the aim of identifying unexplored, prospective areas: the chase for the “West Africa Tupi” is on!
In West Africa the pre-salt exploration is an established play and has been actively explored in-board of the Atlantic Hinge Line (on-shore and in conventional waters) since the 50’s. In 60 years of exploration 109 oil fields have been discovered with cumulative reserves close to 4 Billion of barrels of Oil equivalent (65% on-shore). Apart from a single giant field, few discoveries exceed the 100 MMbbl reserves threshold. The play has not yet reached a mature status, mainly because of geologic complexity and technological challenges involved.
Moreover, the deep-water “golden age” of the post-salt Tertiary turbidite Play (started mid 1990’s and not yet over), mainly in Angola, acted as a catalyst for Majors’ exploration investments. As a result, the pre-salt play out-board of the Atlantic Hinge is virtually un-explored in West Africa.
Eni (formerly Agip) has been a major actor in the region since the beginning of the upstream activities and is today still in the front row to face the exploration challenges of the region. The results of regional geological knowledge and data integration, along with improved seismic depth imaging, is here presented to depict the pre-salt structural and sedimentary evolution along the Gabon, Congo and Angola Aptian Salt Basin, from the onshore hinge to the Continent Ocean Boundary. Although differences in large scale geometries at crustal level and pre-salt sequences subsidence patterns are evident when comparing West Africa and Brazilian margins, evidences supporting the frontier “Tupi” carbonate play on the deep water trend of West Africa are similarly significant. Moreover, the Inner Trend residual potential, on a numbers of proven pre-salt clastic/carbonatic plays, appears under a new light when imaged with state-of-the art seismic imaging and exploration approach.
This might suggest that, probably, that the search for the elusive “West Africa Tupi” should be addressed not only in one direction!
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.