The hidden potential of onshore Angola

Geological map of the Kwanza Basin

Guest post by Alessandro Colla - Trois Geoconsulting

The Angolan basins, from north to south, and in order of their petroleum significance, are the Lower Congo Basin, the Kwanza Basin (with the Benguela Basin) and the Namibe Basin. These form a substantial part of the Aptian Salt Basin that extends from south Cameroon almost to the Namibian border. In recent decades, the sedimentary basins of Angola have been the location of massive oil finds and prolific production in the offshore and these basins and their petroleum systems also extend onshore.

These basins are characterised by 3 primary tectonic phases; a lacustrine latest Jurassic to mid Cretaceous Rift Phase, an episodic marine mid Cretaceous Transitional Phase (during which the mainly Aptian salts were deposited), and a marginal marine to full marine Drift Phase that saw major delta building episodes, deposited under the influence of widespread salt tectonism.

Angola Basemap

The Lower Congo Basin is bifurcated by the Congo River and extends from the Casa Maria Arch in Southern Gabondown to the Ambriz Spur in northern Angola. It has oil production in Angola (mainland and Cabinda enclave) and in both of the Congo republics, whilst in southern Gabon, oil and gas have been discovered but not yet in commercial volumes. The Lower Congo Basin is characterised by world class source sequences in the rift section (lacustrine in both early and late episodes) and in the marine drift phase, significant structural and stratigraphic traps (generated or influenced by rift and salt tectonics), quality reservoirs, both clastic and carbonate, and abundant sealing intervals.

Angola 2D Seismic Example

The onshore discoveries in the Lower Congo Basin came during the height of exploration activity between 1967 and 1992. The early onshore effort resulted in finding some 13 commercial oil fields (one gas field), with reserve sizes varying between 5 and 40 mmbbls of oil. These discoveries all have reservoirs in post-salt drift deposits, primarily Albo-Cenomanian dolomitic limestones of the Pinda formation.

There is much remaining potential to be provided by deeper targets in both the rift and transitional phase reservoirs, and in salt flank targets in the withdrawal grabens. The application of advanced seismic and drilling technologies can provide significant new opportunities for hydrocarbon discoveries.

Angola Licensing Round 2021

ANPG, the Angolan National Agency for Oil & Gas has plans to make available 7 blocks of the Lower Congo onshore in scheduled bidding rounds between 2020 and 2023. 2D Seismic data are brokered through Geopartners and DDMS Lda.