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Transfer Zones and Hydrocarbon Accumulation in the Albertine Graben of the East African Rift System

Abeinomugisha, Dozith *1; Njabire, Nurudin 1
(1) Petroleum Exploration and Production, Ministry of Energy and Mineral Development, Entebbe, Uganda.

Fault systems initiate as simple fractures and propagate radially. As displacement on each fault strand increases, the tips sense and propagate towards each other and eventually link up. The linked system then begins to operate as a single fault segment. The resultant fault segment also propagates radially and may link up with another fault segment to fault a larger fault. The area where fault segments link up is called a transfer zone and is highly deformed. There are two types of transfer zones; accommodation zones and relay ramps. There are several pronounced transfer zones in the Albertine Graben, both accommodation zones and relay ramps. Due to relative displacement on the two linking faults, complex structuring develops in these zones. In the Albertine graben however, the amplitude of the structures especially in the hanging wall indicate that there could be an element of lateral movement along strike.

The Albertine graben forms the northernmost termination of the western arm of the East African Rift System. The rift is highly segmented and bordered by en - echelon linked border faults typically ten to twenty kilometers long. These faults are separated by relay ramps and accommodation zones. The graben, can be divided into three structural domains based on structural geometry and trend; the southern, central and northern domains. These structural domains are separated by accommodation zones.

The Albertine graben has been under exploration for hydrocarbons for over twenty five years. Initial data acquisition concentrated on geological mapping, Gravity and Magnetic data acquisition. The acquired geological data indicated several hydrocarbon seeps distributed along the transfer zones formed by major fault linkages along strike. The acquisition and interpretation of 2D and 3D seismic data have confirmed complex structural patterns in the transfer zones including high amplitude folds and highly faulted blocks. Most of these structures have now been drilled and found to contain hydrocarbons. Currently, significant amounts of discoveries have been made in the Graben that warrant development and production. The trapping mechanism has largely been formed by structures within transfer zones as most of the discoveries to-date are within these zones. Understanding structural evolution within transfer zones is going to play a crucial role in future exploration efforts in the Albertine Graben and the entire East African Rift system.

 

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