3-D Petroleum System Modeling of the Orange Basin, Offshore South Africa

The prospectivity of the Orange Basin offshore the west coast of the Republic of South Africa has been investigated using 3D petroleum system modeling techniques. The 3D model covers an area of 95.600 km2 between 100 - 2850 m bathymetry. The basin geometry and evolution were reconstructed using new maps that were derived from the analysis of an extensive 2D exploration seismic reflection dataset, covering the proximal Late Jurassic rift- and half grabens, the Cretaceous basin depocenter and a Cenozoic prograding wedge in the deep marine distal slope. The sedimentary succession of the Orange Basin consists of more than 8 kms of synrift and drift deposits, related to the continental break-up of Gondwana and the opening of the South Atlantic. The model includes a proven Aptian-Albian source rock and an assumed Cenomanian-Turonian source.

The timing of generation and maturity are modeled using new compositional kinetic models for Aptian-Albian and Cenomanian-Turonian source rocks. These kinetic models were derived from thermally immature, organic-rich black shales from DSDP sites located in the southeast Atlantic. The investigated Aptian-Albian source rocks contain Type II and a mixed Type II/III kerogen, while Cenomanian-Turonian source rocks are highly variable, but show a potential for generation of low wax oils.

Modeling results indicate the main petroleum generation to have occurred during the Late Cretaceous from Aptian-Albian source rocks. A second minor petroleum generation pulse occurs in late Cenozoic times from Aptian-Albian and Cenomanian Turonian source rocks in response to the progradation of Cenozoic clastics sediments towards the deep water Orange Basin.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California