A Reevaluation of the Early Cretaceous and Presalt Prospectivity of the Kwanza Basin Using a Newly Depth-Imaged Seismic Database

Chris Soufleris¹, Mvezi Maziano², Murthy Inkollu², Severino Cardoso², Nora Herbst¹, and Malcolm Francis^1
1Multiclient, WesternGeco, Gatwick Airport, United Kingdom
²Exploration & Production, Sonangol, Luanda, Angola

Exploration in recent years on the South American and West African margins have focused on Upper Cretaceous and Tertiary prospects. More recently, exploration efforts shifted towards the Early Cretaceous and significant presalt discoveries were made in the Santos basin thereby establishing a prolific new play fairway. With Brazil and Angola sharing a similar tectonostratigraphic evolution and similar petroleum systems, this presalt success in Brazil provided fresh impetus to presalt exploration offshore Angola.

Presalt exploration is not new offshore West Africa where there is oil production from presalt reservoirs onshore and offshore Gabon and also presalt discoveries offshore Angola. These efforts, however, have been hindered by poor seismic imaging caused by complex salt and carbonates structures. Such complexities can be correctly accounted for by depth imaging.

We deployed a state-of-the-art preprocessing and depth imaging sequence to reimage an extensive regional library of 2D data in depth. This new database provided a dense (5 to 10 km) and contiguous regional coverage, from the shelf to the ultradeep waters, along both the dip and strike directions. Depth imaging correctly accounted for velocity complexities induced by salt tectonics and deformed carbonates and resulted in a significantly improved image of the presalt section better positioned in space.

The interpretation of the newly depth imaged seismic data allowed us to establish the tectonic framework of the syn-rift and post-rift sections by mapping the fault systems and the major stratigraphic sequences, from basement to seabed. This delineated the presalt grabens and established their trends, connectivity and spatial continuity. In addition, it allowed us to map presalt sequences and structures, similar to those observed offshore Brazil.

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