PETROLEUM GEOLOGY AND HYDROCARBON POTENTIAL OF THE GUBAN BASIN, NORTHERN SOMALILAND
M. Y. Ali*
*The Petroleum Institute, PO Box 2533, Abu Dhabi, UAE.
The Guban Basin is a NW-SE trending Mesozoic-Tertiary rift basin located in northern Somaliland (NW Somalia) at the southern coast of the Gulf of Aden. Only seven exploration wells have been drilled in the basin, making it one of the least explored basins in the Horn of Africa -- southern Arabia region. Most of these wells encountered source, reservoir and seal rocks. However, the wells were based on poorly understood subsurface geology and were located in complex structural areas.
The Guban Basin is composed of a series of on- and offshore sub-basins which cover areas of 100s to 1000s of sq. km and which contain more than 3000 m of sedimentary section. Seismic, gravity, well, outcrop and geochemical data are used in this study to investigate the petroleum systems in the basin. The basin contains mature source rocks with adequate levels of organic carbon together with a variety of reservoir rocks. The principal exploration play is the Mesozoic petroleum system with mature source rocks (Upper Jurassic Gahodleh and Daghani shales) and reservoirs of Upper Jurassic to Miocene age. Maturity data suggest that maximum maturity was achieved prior to Oligocene rift-associated uplift and unroofing. Renewed charge may have commenced during post- Oligocene-Miocene rifting as a result of the increased heat flows and the increased depth of burial of the Upper Jurassic source rocks in localised depocentres. The syn-rift Oligocene-Miocene acts as a secondary objective owing to its low maturity except possibly in localised offshore sub-basins. Seals include various shale intervals some of which are also source rocks, and the Lower Eocene evaporites of the Taleh Anhydrite constitute an effective regional seal. Traps are provided by drag and rollover anticlines associated with tilted fault blocks. However, basaltic volcanism and trap breaching as a consequence of the Afar plume and Oligocene-Miocene rifting of the Gulf of Aden cause considerable exploration risk in the Guban Basin.
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