A. S. Alsharhan1
(1) United Arab Emirates University, U.A.E, Alain, United Arab Emirates
Abstract: New Paleozoic discoveries and Paleozoic petroleum system of the Middle East
Since the beginning of the 20th century more than 500 commercially significant oil and gas fields have been discovered in the Middle Eat. Most of the fields have more than one pay-zone and produce from Mesozoic to Cenozoic shallow water carbonates and clastics. However the discovery of the North Field in Qatar and the Infracambrian oils in Oman has served to stimulate the exploration of deeper horizons.
Between 1989 and 1999 about seventeen oil and gas fields were discovered in central Saudi Arabia in the Permian Unayzah Formation. The Unayzah reservoir is dominated by alluvial and fluvial sequences of sandstone and siltstone or silty sandstones whose reservoir characteristics range from good to excellent with average porosity usually greater than 20% and permeability locally exceeding 4D. The reservoirs contain light (48-52°API gravity), sulfur free (0.02-0.07%) crude oil (Arabian super light) and also sweet gas and condensate (65°API gravity). The source rock for the oil in these reservoirs is the Early Silurian Qusaiba hot shale with a maximum TOC content of 6.15%. It was matured during the late Jurassic with expulsion beginning during early Cretaceous.
The high intensity of seismic surveying and drilling during the nineties led to the discovery of a number of gas and oil in two Paleozoic reservoirs, the deep Haima gas-condensate in North Oman and the overpressured intrasalt Athel oil in South Oman sourced from the Precambrian and Early Cambrian.
In western Iraq high gravity oil (42°API) was discovered in Silurian sandstone and sweet gas in Ordovician sandstone reservoirs. The principal source rock was the highly mature marine shales of Ordovician and Silurian age.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana