The Petroleum Systems and Hydrocarbon Potential of Albertine Graben, East African Rift System – Uganda

Abstract

The Albertine Graben is the Northern most part of the Western arm of the East African Rift System. Proterozoic and Tertiary tectonic events played a major role in the evolution of the basins in this Graben. The ages of the tectonostratigraphic system of the Albertine Graben so far dated range from Miocene to recent. The major structures in Albertine Graben are roll over anticlines, fault blocks, rotated fault blocks and other structures associated with extensional rift system and inversion tectonics. Petroleum Systems modeling of three basins within the Graben suggests that lacustrine source rocks started generating hydrocarbons during the mid-Pliocene and Migration of hydrocarbons into the structures/traps happened during late Pliocene. The results of the numerical modelling together with resource estimates in a number of discoveries indicates that 47billion barrels of oil was generated, and 9-10 billion barrels of oil may be trapped in the undrilled structures or in the undrilled stratigraphic traps. The stratigraphic traps are mainly mapped using seismic data offshore Lake Albert. This interpretation therefore confirms the existence of significant hydrocarbon potential within the Albertine Graben. Like in many rift basins, the petroleum systems of Albertine Graben are characterized by distinct interbedded clastic source-reservoir-seal lithofacies which, in combination with extensional structural traps increases potential for hydrocarbons accumulation. The tectonic evolution of Albertine Graben controlled the essential elements necessary for a petroleum system. A three-stage evolution model has been suggested to have controlled the rift development of Albertine Graben. Five major depocentres have been identified to the western side of the rift which contains the mature source rocks rich in organic matter, deeply buried and overlain by lacustrine deltaic sediments. These make it possible to have the elements of a petroleum system in place before oil migration commenced. This paper will present the early to late syn-rift petroleum plays and correlate them with the confirmed commercial oil discoveries.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018