oa Saudi Aramco Permian-Carboniferous (Unayzah) stratigraphic nomenclature of Saudi Arabia

Saudi Aramco is pursuing an aggressive non-associated gas exploration and development program of Permian- Carboniferous sandstone reservoirs. This has resulted in a considerably increased understanding of the depositional facies, systems tracts, and stratal architecture of these biostratigraphically lean and lithologically heterogeneous siliciclastics, typical of continental successions. Various nomenclatures, which include numerous inconsistencies, are in use throughout the industry with no clear standards that adhere to the rules of stratigraphic nomenclature. A stratigraphic nomenclature is proposed, which defines a number of discrete units within a sequence stratigraphic framework. These sequences can be mapped across Saudi Arabia and into correlative units defined elsewhere on the Arabian Plate. The Unayzah Group is defined as those rocks above the Hercynian unconformity and below the pre-Khuff unconformity. They range in age from mid-Carboniferous to Early Permian. This group is subdivided into the glacio-fluvial to glacio- lacustrine Juwayl Formation, overlain by the postglacial (fluvial, playa and eolian) Nuayyim Formation. The Juwayl Formation is further subdivided into the Serpukhovian? to Asselian Ghazal Member (which includes the Unayzah C Reservoir) and the Asselian to Early Sakmarian Jawb Member (which includes the Unayzah B Reservoir). The Nuayyim Formation is subdivided into the Late Sakmarian Wudayhi Member and the Artinskian Tinat Member (which includes the Unayzah A Reservoir). These newly defined stratigraphic units are separated from each other by unconformities (sensu lato). Middle Permian and younger siliciclastics above the pre-Khuff unconformity retain their original name, the Basal Khuff Clastics. Those rocks contain the Khuff Clastics Reservoir.