Print this pageDual Rifts, Dual Source Systems and Strike-Slip Tectonics: Keys to Oil and Gas in the Ogaden Basin, Ethiopia
DU TOIT, SCHALK R., SAMI KURDY, SEBSIBE HAILE ASFAW and ASSEFA AKLILU GESSESSE
The 350,000 sq km Ogaden Basin has natural oil seeps and oil and gas shows in many of the 47 exploration and development wells drilled to date. The Calub (gas) and Hilala (oil) fields occur in the central part of the basin.
The syn-rift succession in the Ogaden Basin occurs in N-trending (Permian) and NE-trending (Triassic) rifts; and comprises more than 5000 m of continental sediments, and a regional organic-rich interval close to the Permo-Triassic boundary. This unit has also been recognized in Kenya and Tanzania; in Madagascar this interval sourced the deposits of tar sands and heavy oil. The interval is mature along the margins of the Ogaden Basin.
The organic-rich marine post-rift Upper Jurassic Uarandab Shale Formation, attains a thickness in excess of 150 m and reaches oil maturity in the deeper parts of the basin. It is a regional seal to the underlying carbonates of the Hamanlei Formation, and is the suspected source for an oil seep in the western part of the basin.
The Ogaden Basin is dissected by a large number of faults, inclusive of those which are genetically related to the Tertiary Ethiopian Rift. A regional NE-trending right-lateral strike-slip fault system, of possible early Cretaceous age, has been observed as negative and positive flower structures in the subsurface, and may form a key component of traps in the Calub-Hilala area and the central part of the Ogaden Basin.