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Book Chapter

Evolution of the Lower Cretaceous Ratawi Oolite Reservoir, Wafra Field, Kuwait-Saudi Arabia Partitioned Neutral Zone

By
Susan A. Longacre
Susan A. Longacre
Texaco E&P Technology Division 3901 Briarpark - Houston, TX 77042
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Elliott P. Ginger
Elliott P. Ginger
Texaco E&P Technology Division 3901 Briarpark - Houston, TX 77042
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Published:
January 01, 1988

Abstract

The Ratawi Oolite reservoir at the Wafra Field has produced more than 500,000,000 barrels of oil since the middle 1950's from Lower Cretaceous limestones and slightly dolomitized limestones. The Ratawi Oolite is the deepest of several reservoirs in the field, and it is more than 500 feet thick with average porosities ranging from 18 to 25 percent and average permeabilities ranging from 100 md to more than one Darcy. Geological core analysis and log correlations allow the reconstruction of reservoir and non-reservoir horizons across the field.

Contrary to its name, the Ratawi Oolite is composed dominantly of skeletal and peloidal grainstones and mud-lean packstones that accumulated on the crest and around the flanks of a pre-existing bathymetric prominence on the Arabian Shelf. For the most part, sediments that accumulated across the crest of the antecedent structure had appreciable primary reservoir character. In contrast, some flanking equivalent sediments were partly to totally choked with micrite-rich sediment.

Periodically the Wafra structure experienced a relative lowering of sea level, resulting in a 1) highly variable distribution of lithofacies, 2) weathering or chalkification of the already accumulated sediment, and 3) selective layers of calcite cementation that may have been associated with exposure surfaces and freshwater lenses.

Diagenesis had little effect in reducing the capacity of the Ratawi Oolite reservoir: small amounts of rim cement retarded the capacity-reducing effects of compaction. Late non-fabric-selective leaching significantly enhanced the storage capacity and transmissivity of the Ratawi Oolite, resulting in a premium quality reservoir.

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Contents

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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