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Abstract

DOI:10.1306/13351553M1001742

Copyright copy2012 by The American Association of Petroleum Geologists.

Hydrocarbon Prospectivity in Mesozoic and Early–Middle Cenozoic Rift Basins of Central and Northern Kenya, Eastern Africa

Jean-Jacques Tiercelin,1 Peter Thuo,2 Jean-Luc Potdevin,3 Thierry Nalpas4

1UMR 6118 CNRS (Centre National de la Recherche Scientifique) Geosciences Rennes, Universite de Rennes 1, Campus de Beaulieu, Bat. 15, 35042 Rennes Cedex, France; email: [email protected]
2National Oil Corporation of Kenya, Aon Minet Building, Mamlaka Rd., Off Nyerere Rd., P. O. Box 58567-00200 Nairobi, Kenya; email: [email protected]
3Universite de Lille 1, Sciences et Technologies, UFR des Sciences de la Terre, UMR 8157 CNRS (Centre National de la Recherche Scientifique) Geosystemes, 59655 Villeneuve d'Ascq Cedex, France; email: [email protected]
4UMR 6118 CNRS (Centre National de la Recherche Scientifique) Geosciences Rennes, Universite de Rennes 1, Campus de Beaulieu, Bat. 15, 35042 Rennes Cedex, France; email: [email protected]

ACKNOWLEDGMENTS

Permission to conduct field geologic research in the West Turkana Basin was provided by the Office of the President and the Ministry of Education, Science and Technology of the Republic of Kenya (research permits to Jean-Jacques Tiercelin, no. OP/13/001/23C 290 and MOEST 13/001/23C 290). This study was supported by grants from the French Ministry of Foreign Affairs. We are grateful to the National Oil Corporation of Kenya (NOCK) for administrative and logistic support in the field. The authors thank Chris Morley and Ian Hutchinson for their careful reviews and useful suggestions on ways to improve this chapter, as well as the Editor Dengliang Gao for valuable comments at various stages of manuscript preparation. Peter Thuo and Jean-Jacques Tiercelin dedicate this chapter to the memory of F. M. Mbatau, former NOCK exploration manager, who died in a road accident in July 2010.

ABSTRACT

The northern (NKR) and central (CKR) segments of the Kenya Rift are among the most important areas of the East African rift system for hydrocarbon prospecting because they offer the oldest and longest lived sedimentary basins and they are a crossover area between Cenozoic and Cretaceous rifts. During the 1970s and 1980s, the interest of oil companies focused in the Turkana depression and the northeastern region of Kenya. Seismic reflection surveys and several exploration wells enabled the identification of several deeply buried basins: (1) In the NKR, three strings of north–south-oriented half grabens, the oldest known basins being of Cretaceous?–Paleogene to middle Miocene age; (2) In the CKR, two north–south half grabens, the Baringo-Bogoria Basin (Paleogene–Present Term), and the Kerio Basin (Paleogene–upper Miocene). All basins are filled by up to 8 km (5 mi) thick sediments of alluvial, fluviodeltaic, or lacustrine origin and volcanics of late Eocene to Neogene age.

New studies have focused on reservoir and/or source rock quality in several of these basins. In terms of hydrocarbon potential, arkosic sandstones in CKR or NKR demonstrate a fair to good reservoir quality, with porosity up to 25%. Strong changes in terms of diagenetic alteration relate to deformation events or change in sediment source as a result of tectonic activity and hydrothermal fluid circulation associated with volcanism. High-quality source rocks were deposited in freshwater lake environments under a tropical climate. Such environments have been identified during the Paleogene in the NKR and lower Neogene in the CKR. The combination of reservoir and source rock characteristics results in a provisional classification of each studied basin, in terms of very high to medium potential for hydrocarbons.

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