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Permian (Guadalupian) Reservoir Facies, Mc Elroy Field, West Texas

By
Paul M. Harris
Paul M. Harris
Gulf Research & Development Company, P. O. Box 37048, Houston, Texas 77236
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Clive A. Dodman
Clive A. Dodman
Gulf Oil Ras Al Khaimah, P. O. Box 540, Ras Al Khaimah, U.A.E.
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Deborah M. Bliefnick
Deborah M. Bliefnick
Gulf Oil Exploration and Production Co., P. O. Box 36506, Houston, Texas 77236
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Published:
January 01, 1984

Abstract

McElroy Field, situated on the eastern margin of the Central Basin Platform, produces from Upper Permian (Guadalupian) dolomites of the Grayburg Formation. Six lithofacies were recognized in the Grayburg during detailed core and wireline log studies. Stratigraphic relations indicate that prior to deposition of the Grayburg Formation a regression exposed the underlying carbonate platform. During subsequent transgression, open shelf deposits of the Grayburg formed and were overlain by shallow shelf deposits. The capping regressive sequence comprises shallow shelf-to-intertidal sediments of the upper Grayburg and supratidal sediments of the Queen Formation that prograded from west to east across the field.

Approximately 75 percent of the reservoir intervals in the field lie within dolomites of shallow shelf and shallow shelf-to-intertidal origin that contain secondary intercrystalline porosity. Carbonate sands form an important component in these lithofacies. Shallow shelf deposits are homogeneous, unstratified, bioturbated dolowackestones and dolopackstones. Vertical continuity within this zone is good, despite localized nonporous zones due to sulphate cementation. Shallow shelf-to-intertidal deposits are stratified and show abrupt lithological variation vertically and horizontally. Accompanying this variation are changes in porosity and permeability. Dolograinstones and dolopackstones comprising this facies are porous along the crest of the structure and nonporous on the flanks. Numerous laterally continuous barriers to vertical permeability are formed where porosities are cemented with sulphates, making correlation of pay zones and prediction of continuity between wells difficult.

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Contents

SEPM Core Workshop Notes

Carbonate Sands-A Core Workshop

Paul M. Harris
Paul M. Harris
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SEPM Society for Sedimentary Geology
Volume
5
ISBN electronic:
9781565762602
Publication date:
January 01, 1984

GeoRef

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