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ABSTRACT: Geology and Hydrocarbon Potential in the State of Qatar, Arabian Gulf

A. S. Alsharhan, A. E. M. Nairn

The state of Qatar is situated in the southern Arabian Gulf and covers an area of 12,000 km2. It is formed by a large, broad anticline, which is part of the regional south-southwest-north-northeast-trending Qatar-South Fars arch. The arch separates the two Infracambrian salt basins. The Dukhan field was the first discovery, made in 1939, in the Upper Jurassic limestones. Since then, a series of discoveries have been made so that Qatar has become one of the leading OPEC oil states.

Hydrocarbon accumulations are widely dispersed throughout the stratigraphic column from upper Paleozoic to Cretaceous producing strata. The most prolific reservoirs are the Permian and Mesozoic shelf carbonate sequences. Minor clastic reservoirs occur in the Albian and Paleozoic sequences.

Seals, mainly anhydrite and shale, occur both intraformationally and regionally. Several stratigraphic intervals contain source rocks or potential source rocks. The Silurian shales are the most likely source of the hydrocarbon stored in the upper Paleozoic clastics and carbonates. The upper Oxfordian-middle Kimmeridgian rocks formed in the extensive starved basin during the Mesozoic period of sea level rise. Total organic carbon ranges between 1 and 6%, with the sulfur content approximately 9%. The source material consists of sapropelic liptodetrinite and algae.

The geological background of the sedimentary facies through geologic time, stratigraphy, and structural evolution, which control source, and the subsequent timing and migration of large-scale hydrocarbon generation, are presented in detail.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990