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Stratigraphy, Stable Isotopes, and Hydrocarbon Potential of the Aptian Shuaiba Formation, U.A.E.

By
Abdulrahman S. Alsharhan
Abdulrahman S. Alsharhan
Faculty of Science, United Arab Emirates University, P.O. Box 17551, Al Ain, U.A.E.
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;
Ihsan S. Al-Aasm
Ihsan S. Al-Aasm
College of Engineering and Sciences, Department of Earth Science, University of Windsor, Windsor, Ontario, N9B 3P4, Canada.
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;
Mohamed G. Salah
Mohamed G. Salah
Faculty of Science, United Arab Emirates University, P.O. Box 17551, Al Ain, U.A.E. Present address: Reservoir Characterization Research & Consulting (UK) Ltd., P.O. Box: 46800, Abu Dhabi, U.A.E.
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Published:
January 01, 2000

Abstract

The Shuaiba Formation of the United Arab Emirates (U.A.E.), forms one of the most important petroleum reservoirs in the Arabian Gulf. Its reservoir quality is controlled by diagenetic processes that were active during early shallow burial to late deep burial. Detailed well log evaluation, petrographic and geochemical studies of carbonate diagenesis, X-ray diffraction, cathodoluminescence microscopy, and oxygen and carbon isotopic determinations from cores and an outcrop section allowed evaluation of the stratigraphic and depositional framework of the Shuaiba Formation, its diagenetic history, and the prediction of its local reservoir potential. The Shuaiba Formation consists of two informal and one formal members: the lower Shuaiba and upper Shuaiba members and the Bab Member, in ascending order. The Shuaiba ranges in thickness from 45 to 145 m, having accumulated in a wide range of depositional settings from shallow to deep shelf. The lithofacies identified within the Shuaiba Formation include peloidal skeletal algal packstone/grainstone; ooidal-peloidal grainstone/packstone; skeletal algal (Lithocodioidea) floatstone; intraclastic and coated packstone/grainstone and skeletal wackestone/ packstone. These facies were deposited during third-order depositional sequences, including two transgression system tracts (TST) separated by a highstand system tracts (HST). Diagenetic alteration of the original carbonate components proceeded through marine, shallow burial, and deeper burial settings related to stabilization of the carbonate matrix, cements, and rudist shells. Oxygen and carbon isotopes of calcific matrix have the least altered components of these rocks (av. δ180 = 5.7%o PDB; δ13C = +2.5 %o PDB), whereas the calcite cements occluding shell porosity and veins have more depleted isotopic values (av. δ180 = 8.8%o PDB;δ13C = +0.5%o PDB). The variations of oxygen and carbon isotopes reflect changes in the water-rock interactions and increasing burial.

The carbonates of the lower and upper Shuaiba members have porosities between 12% and 32% and permeabilities between 1.0 and 160.0 md. The reservoir quality is highly affected by the diagenetic processes which include stabilization of metastable carbonate phases, cementation, dolomitization, stylolitization, and dissolution. The Bab Member, which was deposited in a basinal setting, is organically rich and forms substantial source rock in the eastern and northeastern parts of central UAE and is mature enough in deep troughs to generate and expel hydrocarbons to the reservoirs.

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SEPM Special Publication

Middle East Models of Jurassic/Cretaceous Carbonate Systems

Abdulrahman S. Alsharhan
Abdulrahman S. Alsharhan
Faculty of Science United Arab Emirates University, P.O. Box 17551, Al Ain, U.A.E.
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;
Robert W. Scott
Robert W. Scott
Precision Stratigraphy Associates, RR3 Box 103-3, Cleveland, OK 74020, U.S.A.
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SEPM Society for Sedimentary Geology
Volume
69
ISBN electronic:
9781565761919
Publication date:
January 01, 2000

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