Abstract

The United Arab Emirates is located on the stable Arabian foreland of the Arabian plate and is separated from the unstable Iranian fold belt by the Arabian Gulf. During the Late Paleozoic (Upper Permian) to the Cenozoic (Tertiary) Eras the vast Arabian platform lay along the southern margin of the Tethys Ocean. During this period epeiric shelf carbonates associated with only minor clastics and evaporites were deposited. Sedimentation patterns were controlled by many factors such as epeirogenic vertical movements due to basement tectonism, halokinesis, climatic variations, and, most importantly, sea-level variations. The Late Paleozoic to Cenozoic stratigraphic sequence shows lateral variations in formation thicknesses as well as in the distribution and continuity of lithofacies characteristics.

Abundant giant oil and gas reservoirs have been found in Jurassic (Araej and Arab) and Cretaceous (Habshan, Lekhwair, Kharaib, Shuaiba, Mishrif, and Simsima) formations. Gas was discovered in the Upper Permian (Khuff Formation) carbonates in offshore and Upper Jurassic (Arab Formation) carabonates in onshore Abu Dhabi. Most hydrocarbon accumulations are related to structural traps, although combined stratigraphic-structural or stratigraphic traps exist in some areas. In western Abu Dhabi, most of the oil and gas are in Jurassic reservoirs, whereas in the central areas most of the oil is in Lower Cretaceous reservoirs. In the eastern offshore areas (Abu Dhabi and Dubai), oil and gas reservoirs are of Permian and Middle Cretaceous with minor production from Lower Cretaceous intervals. In western Abu Dhabi, structural traps started developing in the Upper Jurassic, getting progressively younger toward the east. The main (peak) tectonic event that shaped most of the structures occurred at the end of the Middle Cretaceous and was related to the obduction of the Oman Ophiolite and the formation of the Oman Mountains.

The Tithonian Hith Anhydrite and the Albian Nahr Umr Shale are the two principal sealing formations of the oil and gas accumulations in the Jurassic and Cretaceous reservoirs. However, secondary seals and barriers also exist throughout the stratigraphic sequence. The Silurian Qusaiba Formation is the main source rock for the Permian gas reservoirs. The Upper Jurassic Diyab/Hanifa Formation and the Middle Cretaceous Shilaif/Khatiyah Formation are the main source rocks for the giant Jurassic and Cretaceous carbonate reservoirs, respectively. Other potential source rocks are also identified within the Lekhwair and Shuaiba (Bab Member) Formations.