PETROLEUM BASINS OF YEMEN: THEIR TECTONIC DEVELOPMENT AND LITHOSTRATIGRAPHY

Located in the southwestern corner of the Arabian Peninsula, Yemen was the last country in the Middle East where oil was discovered (in 1984 by Hunt Oil). Following the unification of North Yemen and South Yemen in 1990, the country became an active scene for oil exploration and production. This paper describes the updated stratigraphy, structural framework and evolution, and hydrocarbon prospectivity of the Paleozoic, Mesozoic and Cenozoic basins of Yemen. The Paleozoic basins include (1) the Rub’ Al-Khali basin (southern flanks), bounded to the south by the Hadramawt arch (oriented approximately W-E) towards which the Paleozoic and Mesozoic sediments pinch out; (2) the San’a basin, encompassing Paleozoic through Upper Jurassic sediments; and (3) the southern offshore Suqatra (island) basin filled with Permo-Triassic sediments correlatable with that of Karoo rift in Africa. The Mesozoic rift basins formed during the breakup of the Gondwana supercontinent and the separation of India/Madagascar from Africa-Arabia during the Late Jurassic/Early Cretaceous. The five Mesozoic sedimentary rift basins reflect in their orientation an inheritance from deep-seated, reactivated NW-SE trending Infracambrian Najd fault system. These basins formed sequentially from west to east and to southeast, sub-parallel with rift orientations. The Sab'atayn and Say'un-Masilah basins provide the only producing oil and gas fields so far. Petroleum reservoirs in both the basins have been charged from the Upper Jurassic Madbi shale. The main reservoirs in the Sab’atayn basin include sandstone units within the Sab’atayn Formation (Tithonian), turbiditic sandstones of the Lam Member (Tithonian), and the Proterozoic fractured basement (upthrown fault blocks), while the main reservoir in the Say’un-Masilah basin is the sandstone of the Qishn Clastics Member (Lower Cretaceous). The Cenozoic rift basins are related to the separation of Arabia from Africa by the opening of the Red Sea to the west and the Gulf of Aden to the south of Yemen during the Oligocene-Recent. These basins are filled with sedimentary successions up to 3 km, showing both lateral and vertical facies changes. The Cenozoic rift basins along the Gulf of Aden include the Mukalla-Sayhut, the Hawrah-Ahwar, and the Aden-Abyan basins (all trending ENE-WSW) and have both offshore and onshore sectors as extensional faulting and regional subsidence affected the southern margin of Yemen episodically. Sea-floor spreading in the Gulf of Aden dates back to the Late Miocene. Many of the offshore wells drilled in the Mukalla-Sayhut basin have encountered oil shows in the Cretaceous through Neogene layers. Sub-commercial discovery was identified in Sharmah-1 well in the fractured Middle Eocene limestone of the Habshiyah Formation. The Tihamah basin along the NNW-SSE trending Red Sea commenced in Late Oligocene, with oceanic crust formation in the Pliocene. The Late Miocene stratigraphy of the Red Sea offshore Yemen is dominated by salt deformation. Oil and gas seeps are found in the Tihamah basin including the As-Salif peninsula and the onshore Tihamah plain; and oil and gas shows encountered in several onshore and offshore wells indicate presence of proven source rocks in this basin.