Abstract

The purpose of this paper is to provide an overview of petroleum occurrence and provenance for the 1000 km West African Atlantic Margin from Cabinda to mid-Angola. Over this margin the Lower Congo Coastal and Kwanza provinces cumulatively account for reserves of c. 6 gigabarrels oil recoverable (GBOR). These are dominantly reservoired in Pinda carbonate traps of the former basin. However, with production from a range of aggradational wedge, carbonate platform and pre-salt reservoirs, a diversity in oil character presupposes complex hydrocarbon habitats charged by multiple sourcing.
Each of these two major Atlantic margin salt basins constitutes a different, source rock driven, hydrocarbon habitat. As classic passive margin pull-apart basins, Early Cretaceous initiated rift events (Pre-rift, Syn-rift I, II, etc.) evolved into the drift phase opening of the southern Atlantic. A striking feature of this progression was widespread evaporite deposition of the Aptian Loeme salt. This separates two distinct sedimentary and tectonic domains of the Pre- and Post-Salt.
The core Lower Congo Coastal habitat is dominated by the Pre-Salt Bucomazi Formation sourced ‘poly’ petroleum system. These lacustrine, often super-rich, sediments reveal considerable organofacies variations between their basin fill (Syn-rift I) and sheet drape (Syn-rift II) development, accounting for the compositional diversity in their progenic petroleums. Of crucial impact is a cognate diversity in their kerogen kinetic behaviour. This controls the conditions and timing of generation and realization of charge potential.
With the Lower Congo Coastal habitat extending southwards towards the Ambriz Spur, the Bucomazi facies proper appears restricted to the northern and deeper proto-lake trend. Over the more weakly subsident margins such troughs host inferior sheet drape potential. Elsewhere, Upper Cretaceous-Palaeogene marine clastic Iabe Formation sourced petroleum systems are hydrocarbon productive, yielding petroleums of unique, and/or mixed Pre-Salt hybrid, source provenance.
A less attractive Pre-Salt source system is reflected in the Kwanza habitat. Consequential effects of salt movement have proved important for halokinetic induced structuration, Cretaceous block rafting and pseudograben (Tertiary trough) source deposition. Marginal reserves of Infra-Cuvo and Cuvo derived petroleums are known. With limitations in charge potential at this level, the modest Kwanza reserves (0.1 GBOR) have a Post-Salt provenance deriving primarily form the Eocene Margas Negras and subordinate Aptian Middle Binga sourced petroleum systems. Cases of multi-sourced hybrid petroleums abound. In addition to the organic-rich Albian micrites, Upper Cretaceous black shales provide unproven possible offshore potential.

Get full access to this article

Purchase, subscribe or recommend this article to your librarian.

Information & Authors

Information

Published In

cover image Geological Society, London, Special Publications
Geological Society, London, Special Publications
Volume 1531999
Pages: 181 - 194

History

Published in print: 1999
Published online: 7 June 2022

Authors

Affiliations

R. Burwood
Fina Exploration LtdFina House, 1 Ashley Avenue, Epsom, KT18 5AD, UK

Metrics & Citations

Metrics

Article Usage

Downloaded 0 times

Citations

Export citation

Select the format you want to export the citation of this publication.

View Options

Get Access

Restore your content access

Enter your email address to restore your content access:

Note: This functionality works only for purchases done as a guest. If you already have an account, log in to access the content to which you are entitled.

View options

PDF/ePub

View PDF/ePub

Media

Figures

Other

Tables

Share

Share

Copy the content Link

Share with email

Email a colleague

Share on social media

Suggested Content