--> Abstract: Depositional Setting of Cretaceous Reservoirs, Southern Yemen and Northern Somalia, by Osman Salad Hersi and Dale Leckie; #90077 (2008)

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Depositional Setting of Cretaceous Reservoirs, Southern Yemen and Northern Somalia

Osman Salad Hersi1* and Dale Leckie2
1Sultan Qaboos University, Oman
2Nexen, Canada
*[email protected]

The Say’un-Al Masila Basin of southern Yemen and the Al Mado Basin of northern Somalia are Mesozoic sedimentary basins developed during the disintegration of Gondwana. The two basins formed one single rift (Say’un-Al Mado Graben) with intermittent tectonic disturbances, which affected the carbonate-clastic basin-fill architecture. The Cretaceous Say’un-Al Mado graben had a funnel shape in plan view, tapering northwestward (in Yemen) and open southeastward (through northern Somalia) to the Tethys Ocean. The Cretaceous fill of the Say’un–Al Mado rift consists of siliciclastic sequences predominant in the western flanks of the basin (Tawila Group in Yemen and Yesomma Formation in northern Somalia), and carbonate sequences predominant in the southeastern areas (Mahra Group and Tisje Formation, respectively). The sandstones of the Tawila Group (Qishn and Harshiyat formations) and the Yesomma Formation were deposited in a complex system of braided to low sinuosity meandering rivers, tidal-dominated estuarine and deltaic environments. The terrigenous influx decreased southeastward where carbonate sedimentation flourished in a shallow-marine environment (Mahra Group in Yemen and Tisje Formation in northern Somalia). Carbonate sand shoals, lagoonal wackestones, mudstones and rudistic buildups are the main lithofacies of the carbonate strata. The Qishn Formation is highly porous (18 to 23%) and permeable (up to ten darcies) and contains estimated reserves of over one billion barrels of recoverable oil. Unlike the relatively strong hydrocarbon exploration activity in Yemen, Somalia’s hydrocarbon resources are under-explored. However, the little geological knowledge from the Yesomma and Tisje formations implies they contain good reservoir intervals (up to 300 m thick and 14% porosity) with interbeds of source shales. Many of the drilled wells contain oil stains and gas shows. Maturity of these hydrocarbons ranges from immature to post-mature with good intervals within the oil window.

 

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain