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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 77 (1993)

Issue: 11. (November)

First Page: 1971

Last Page: 1988

Title: Stratigraphic Sequence, Microfacies, and Petroleum Prospects of the Yamama Formation, Lower Cretaceous, Southern Iraq

Author(s): Fadhil N. Sadooni (2)


The Lower Cretaceous Yamama Formation basin was deposited over two tectonic regimes, the northeastern flank of the stable Arabian platform and the unstable zone of the Mesopotamian foredeep. This situation and the probable syntectonic deposition of the formation over growing structures created complex carbonate lithologies. From this tectonic configuration and the facies distribution, it seems that the Yamama Formation was deposited in a setting that changed from an inner to an outer ramp. Along the hinge line separating those two tectonic units, oolite shoals developed. The crestal areas of the growing structures were occupied by stromatoporoid-sponge-coral reefs and oolitic facies. The areas between reefs were the sites of carbonate mud accumulation.

For the purposes of regional correlation and reserve estimation, the Yamama Formation is divided into five lithologic units: three reservoir units, designated from top as YR-A, YR-B, and YR-C, separated by two permeability barrier units, YB-1 and YB-2. These reservoir units are thought to be at least partially isolated from each other.

The best oil prospects are within the oolite shoals and the patch reef buildups in the crestal parts of the structures.

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