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The Eocene Reservoirs of Wafra Field Kuwait/Saudi Arabia Partitioned Neutral Zone

By
H. M. C. Danielli
H. M. C. Danielli
Texaco E&P Technology Division Houston, Texas 77042
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Published:
January 01, 1988

Abstract

The Eocene reservoirs of Wafra Field produce from dolostones with porosities reaching 45 percent and permeabilities that exceed lOOOmd in places. The original sediments were deposited in coastal environments ranging from shallow subtidal to supratidal sabkhas, with mainly high water salinities. Slight changes in relative sea level or climate led to the deposition of sulfate-rich units that can be traced across the entire field.

Fossils present include miliolid foraminifera, ostracodes and cyanobacteria, with rare occurrences of rotaliid foraminifers, dasyclads and echinoderms. Other grain types include pellets, intraclasts and desiccation flakes. The depositional textures of the sediments varied from grainstone to mudstone. The micrite content of these sediments controlled the hydrodynamic properties of the rocks during diagenesis, so that the effects of diagenesis were greatest in rocks that contained little micrite.

Diagenesis consisted of initial marine cementation, compaction, dolomite replacement and overgrowth precipitation, sulfate precipitation, and sulfate breakdown to calcite and sulfur. Leaching by relatively fresh water occurred at several times. Intercrystalline porosity, the main pore system in the reservoirs, developed as a result of dolomite replacement. Pore and pore throat size vary with crystal size and depend on the depositional texture of the rock. Grainstones suffered the greatest amount of alteration and tend to have the largest crystal sizes, whereas mudstones retain their fine crystal size and low permeabilities. The original, depositional heterogeneities of the reservoirs are thus preserved despite the extent of the diagenetic changes.

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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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