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Giant Gas Accumulation in a "Chalky"-Textured Micritic Limestone, Lower Cretaceous Shuaiba Fm. Eastern United Arab Emirates

By
Stephen O. Moshier
Stephen O. Moshier
University of Kentucky Lexington, Kentucky 40506
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Robert W. Scott
Robert W. Scott
Amoco Production Company Tulsa, Oklaholma 74102
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C. Robertson Handford
C. Robertson Handford
University of Arkansas Fayetteville, Arkansas 72701
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Robert D. Boutell
Robert D. Boutell
Amoco Production Company Houston Texas 77253
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Published:
January 01, 1988

Abstract

Sajaa field is a giant gas and gas condensate reservoir located in Sharjah, U.A.E. Production is from the Lower Cretaceous Thamama Group. Lithologies and reservoir characteristics are typified by its uppermost unit, the Shuaiba Formation. Facies in the Shuaiba were deposited in a open-shelf setting, near a ramp or a mound complex. Deposits include rudist and coralgal patch reefs or biostromes with wackestone/packstone depositional textures, Orbitolina -rich wackestones and few peloidal grainstone/packstones. Microporosity in micritic lithofacies is responsible for reservoir quality in the sequence. Microporosity of up to 25% in some beds imparts a "chalky" texture to the rock. Microporosity cannot be related to leaching during post-depositional emergence of the Shuaiba, as suggested for other equivalent-aged mideastern reservoirs. Matrix is composed of euhedral to subhedral microrhombic calcite crystals with average diameters of 4-6 μm. Intercrystalline micropore space reflects arrested cementation of matrix rather than dissolution along crystal contacts. Diagnostic features of emergence are lacking in core below the upper contact of the formation. Matrix microporosity appears to have been an early-developed property of micritic limestones over several hundreds of feet of section at Sajaa field. Microporosity is decreased in zones of intense stylolitization. Open fractures that are partially filled by authigenic kaolinite and coarse calcite spar near the top of the formation are interpreted to be of tectonic origin, occuring after deep burial.

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SEPM Core Workshop Notes

Giant Oil and Gas Fields: A Core Workshop

Anthony J. Lomando
Anthony J. Lomando
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Paul M. Harris
Paul M. Harris
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SEPM Society for Sedimentary Geology
Volume
12
ISBN electronic:
9781565761001
Publication date:
January 01, 1988

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