The Tectono-Stratigraphic Development of Tertiary Depocentres in the Lower Congo Basin, Deepwater Angola

David Johnstone¹, Tim Bird¹, Lourenco Joachim², and Jose G. Jose^2
1PGS Reservoir, Maidenhead, United Kingdom
²Sonangol, Luanda, Angola

A merged 3D seismic volume of approximately 16,500 square kilometers has been created covering Blocks 17, 18, and 34 in the offshore Lower Congo Basin, Angola. This dataset has been used to map the position of Tertiary depocentres through time and compare the prospectivity in the prolific northern part of the study area to that further south.

Eight key, regionally-persistent, horizons have been interpreted, and tied to available well data. These horizons span the top of the pre-salt rift sequence to the top Miocene. The structures at top salt show NW-SE trending salt stocks and discontinuous walls in the north, compared to prominent NNE-SSW trending walls, with freeboard structures up to 650m high, in the south. In the southern area the higher amplitude of the salt structures controls sand deposition to a much larger extent, than is the case to the north.

A series of isochron maps have been completed, which show how the location of sand-rich minibasins changes through the Tertiary period. This change results from the timing of both extensional faulting and salt movement, along with regional factors such as the interplay between sea level changes and variations in sediment input volumes.

Key faults have been analysed and the timing of main phases of extension calculated and compared across the region. This is then used in conjunction with the geometric relationships of the sediment deposited around the salt diapirs, to illustrate the tectono-stratigraphic development of the prospective Tertiary interval across the study area.

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