Stratigraphy, Stable Isotopes, and Hydrocarbon Potential of the Aptian Shuaiba Formation, U.A.E.
Abdulrahman S. Alsharhan, Ihsan S. Al-Aasm, Mohamed G. Salah, 2000. "Stratigraphy, Stable Isotopes, and Hydrocarbon Potential of the Aptian Shuaiba Formation, U.A.E.", Middle East Models of Jurassic/Cretaceous Carbonate Systems, Abdulrahman S. Alsharhan, Robert W. Scott
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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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Middle East Models of Jurassic/Cretaceous Carbonate Systems
This volume will interest tectonic modelers, stratigraphers, sedimentologists, and explorationists. It is the product of the international conference of “Jurassic/Cretaceous Carbonate Platform-Basin Systems, Middle East Models” that was convened in December 1997 jointly by SEPM (Society for Sedimentary Geology) and the United Arab Emirates University in Al Ain, United Arab Emirates. The twenty-three papers present new data and interpretations arranged in three sections: 1) sequence stratigraphy, cyclostratigraphy, chronostratigraphy, and tectonic influences, 2) depositional and diagenetic models of carbonate platforms, and 3) hydrocarbon habitat and exploration/development case studies. New tectonic models of the Arabian Basin, new stratigraphic and sequence stratigraphic reference sections, new geochemical and source rock data, and new reservoir data are presented. New geologic models make this set of papers relevant to geoscientists working outside of Arabia also.