ABSTRACT

The offshore of the United Arab Emirates (U.A.E.) contains eight diapiric islands; Dalma, Zirkouh, Qarnain, Das, Sir Bani Yas, Arzana, Sir Abu Nuwair and Abu Musa. These islands and Jebel Dhanna Peninsula owe their relief to the diapiric movement of salt which has pierced and deformed the overlaying strata.

These diapiric islands have similar shapes, stratigraphic sequences, areal distribution of the identified stratigraphic units and general tectonic framework. With the exception of Das Island, the stratigraphic sequence on the surface of all the diapiric islands consists, in ascending order, of: 1) Infracambrian to Cambrian (Hormuz Group) composed of igneous and metamorphic rocks, salt, anhydrite, carbonate and clastic interbeds; 2) Miocene composed of sandstone, siltstone, shale, carbonate and evaporite interbeds; and, 3) Pliocene to Recent sediments composed of mixed facies of clastics, carbonates and evaporites.

The structural configuration and the tectonic development of the Arabian Gulf Basin played an important role in the salt movement, which enhanced the formation and distribution of the islands, the timing of hydrocarbon generation, migration, and entrapment in the surrounding fields. The U.A.E., one of the world's richest in oil reserves, has almost 200 billion barrels (Bbbl) of oil and 275 trillion cubic feet (TCF) of gas that is sourced mainly from the Upper Jurassic and Lower to Middle Cretaceous formations and accumulated in carbonate reservoirs that range in age from upper Paleozoic to Oligo-Miocene. The geophysical and the geological data revealed three trap geneses in the U.A.E.: 1) Salt-related; 2) basement-related; and, 3) fold belt (collision) traps. Salt-related oil fields of the U.A.E. offshore area are characterized by: (a) dome-shaped structures; (b) independent closures; (c) radial faults within the structures; and, (d) multi-step structural growth histories. Subtle turtle structures exist between the diapiric islands of the U.A.E.. These structures form fields at Hair Dalma and Dalma, near Dalma Island, Mandous field, near Sir Abu Nuwair Island, and Mubarek field near the Abu Musa Island. The quality of the carbonate reservoir in the salt related oil fields is attributed to the effects of the diapiric salt movement.

RESUME

Huit iles diapires se situent au large des Emirats arabes unis (EAU); Dalma, Sirkouh, Qarnain, Das, Sir Bani Yas, Arzana, Sir Abu Nuwair et Abu Musa. Ces iles et la peninsule Jebel Dhanna doivent leur relief au mouvement diapire de sel qui a perce et deforme la couche sus-jacente.

Ces iles diapires ont des formes, des sequences stratigraphiques, une distribution de surface des unites stratigraphiques identifiees et un cadre tectonique general semblables. Sauf pour l'ile de Das, la sequence stratigraphique a la surface de toutes les iles diapires consistent, par ordre ascendant, de: 1) l'Infracambrien au Cambrien (groupe Hormuz) compose de roches magmatiques et metamorphiques, de sel, d'anhydrite, de roches de carbonate et clastique interstratifies; 2) le Miocene compose de gres, d'aleuronites, de schistes, de roches carbonates et d'evaporites interstratifies et 3) sediments du Pliocene a l'Holocene composes de facies mixtes, de clastiques, de carbonates et d'evaporites.

La configuration structurale et le developpement tectonique du bassin du golfe d'Arabie joue un role important au mouvement du sel, qui a rehausse la formation et la distribution des iles, le minutage de la generation d'hydrocarbure, la migration et le piegage dans les champs environnants. Les EAU, une des reserves de petrole les plus importantes au monde, possede 200 milliards de barils (Bbbl) de petrole et 275 billions de pieds cubes de gaz provenant surtout du Jurassique superieur et des formations du Cretace inferieur a moyen et accumule surtout dans les reservoirs de carbonates d'age s'echelonnant du Paleozoique superieur a l'Oligo-Miocene. Les donnees geophysiques et geologiques ont revelees trois origines de pieges dans les EAU: 1) connexe au sel; 2) connexe au sous-sol et 3) pieges de plissement

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(collision). Les champs petroliferes relies au sel de la region au large des EAU sont caracterises par: a) des structures en forme de domes, b) des fermetures independantes, c) des radiales dans les structures et d) des historiques de croissances structurelles a plusieurs etapes. Des structures de nodules discretes existent entre les iles diapires des EAU. Ces structures forment les champs a Hair Dalma et Dalma, pres de l'ile d' Abu Musa. La qualite du reservoir de carbonate dans les champs petroliferes relies au sel est attribuee aux effects des mouvements de sel diapire.

Traduit par Marie-Louise Tomas