Geology and hydrocarbon habitat in the Arabian Basin: the Mesozoic of the State of Qatar

Abstract

The State of Qatar is situated in the southwestern Arabian Gulf and covers an area of about 12 000 sq km. The land portion is formed by a large, broad arch, which is part of the regional, NE-SW trending Qatar-South Fars Arch, separating two Infracambrian salt basins. The Dukhan Field on the west coast of the Qatar Peninsula, with its reservoirs in Upper Jurassic limestones, was the first oil field discovered. Since this discovery in 1940, a series of other discoveries have been made, and Qatar became a member of the Organization of Petroleum Exporting Countries (OPEC) in 1973. Hydrocarbon accumulations are widely dispersed throughout the stratigraphic column with production from Middle Jurassic to Middle Cretaceous strata. The most prolific reservoirs are in shelf carbonate sequences and minor accumulations occur in Albian clastic sediments. Seals, mainly anhydrite and shale, occur as formations of regional extent as well as intraformationally with smaller areal distributions. There are several stratigraphic intervals which contain source rocks or potential source rocks. Upper Oxfordian-middle Kimmeridgian source rocks were formed in an extensive, starved basin during a period of sea-level rise. They contain organic matter of sapropelic, liptodetrinitic and algal origin and have a total organic carbon content of 1 to 6%. Both depositional environment and tectonic evolution through geologic time have influenced sedimentary facies and stratigraphic features, which controlled reservoir, source and seal characteristics and subsequent hydrocarbon generation, migration and entrapment.