The Sahmah Formation (Safiq Group, Haima Supergroup) of Oman is divided into a lower ‘Shale Member’ (or ‘Sahmah Shale’), and an upper ‘Sandy Member’. The Shale Member was deposited in a deep-marine environment, and the Sandy Member in a marginal marine setting. The formation is greater than 500 meters thick in the Burkanah-1 exploration well, located in south Oman along the eastern edge of the Rub’ Al-Khali Basin. In many areas in Oman, the formation is absent due to erosion by the ‘Hercynian’ unconformity. The age of the Sahmah is generally interpreted as Early Silurian Llandovery; however, recent biostratigraphic studies suggest that it may range in age from latest Ordovician Ashgill to Llandovery. The basal Sahmah Shale (3–10 meters thick) is an excellent source rock, as confirmed by its correlation to the ‘B’ oil in the overlying Permian Gharif Formation in the Sahmah field in central Interior Oman. This study combined new and previously acquired geological data from 16 wells in Oman, and includes source rock analytical data. A basin model was used to assess the maturation history of the Sahmah Shale, and the hydrocarbon potential of two associated petroleum systems. The first system occurs along the ‘Hercynian’ erosional edge of the Sahmah source rock. The migration pathway involves vertical charging of the overlying Upper Carboniferous-Lower Permian Al Khlata Formation or/and the Permian Gharif Formation. This area constitutes the Sahmah Shale:Gharif Formation(!) Petroleum System. The second Petroleum System, the Sahmah Shale:Hasirah Formation(?), applies to regions where the Sahmah is thick, and intra-Sahmah shales act as a seal. In these regions, if the shale is mature and the pre-Sahmah section is porous, then down charging provides the migration pathway to the trap.

The Sahmah Formation (Safiq Group, Haima Supergroup) of Oman is divided into a lower ‘Shale Member’ (or ‘Sahmah Shale’), and an upper ‘Sandy Member’. The Shale Member was deposited in a deep-marine environment, and the Sandy Member in a marginal marine setting. The formation is greater than 500 m...