Stratigraphy of the Wajid Sandstone of Southwestern Saudi Arabia

ABSTRACT Until recently, the relatively monotonous, thick sequence of Wajid Sandstone which crops out in southwestern Saudi Arabia has been mapped as a single lithologic unit with a Cambrian-Ordovician age. Seismic ties to the outcrop, recent fieldwork by Bureau de Recherches Geologiques et Mineres (BRGM) and Saudi Aramco' geologists and stratigraphic information obtained from a shallow 2260-foot test well (V-608) suggest that the Wajid Sandstone (as mapped in the outcrop) may be divided into five units and that the rocks range in age from Silurian and older to Permian. From oldest to youngest, the five units are the Saq and Qasim formations undivided (Cambrian-Ordovician age), the Zarqa and Sarah formations (Late Ordovician to Early Silurian age), the Qalibah Formation of Early Silurian age, rocks of Devonian to Middle Carboniferous age undivided, and the Unayzah Formation (Haushi Group) of late Carboniferous to Early Permian age. Except for the Qalibah Formation which is the source-rock of recently discovered oil in the Hawtah, Dilam, Raqhib, Nuayyim and Hazmiyah fields to the north, all of these Paleozoic sands have excellent reservoir potential in the subsurface. It is proposed that the term Wajid Sandstone be dropped from usage and that the existing Paleozoic nomenclature discussed above and used by Saudi Aramco be applied to the Wajid Sandstone outcrop.