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Introduction

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Published:
January 01, 1993

Abstract

In carbonate systems, dolomite often forms the best reservoirs. The dolomitization of carbonate sediments and rocks increases crystal size and pore throat size, and decreases pore roughness. Without exception, the combination of these increases the permeability of the carbonate. In this way, dolomitization “makes” the reservoir, with dolomite serving as the reservoir and the surrounding limestone forming the seal. Porosity in the dolomitic facies is enhanced in such cases not so much as a result of dolomitization, but through leaching of skeletal grains or evaporites, or by fracturing.

Many environments of dolomitization have been identified. Some result in unique reservoir geometries that bear directly on exploration strategy. Therefore, it is important to gain a firm understanding of the process which controlled dolomitization early in the exploration history of a basin.

In addition, dolomite is less reactive than calcite, so dolomite units are more resistant to porosity loss with depth than limestone units (Fig. 1) and the depth to “economic basement” is commonly greater for dolomite than for limestone. Therefore, the spatial distribution of dolomitized intervals within a carbonate section often defines the limits of reservoir development. The hydrologie process that dolomitizes a limestone can control the morphology of the dolomite body as well (e.g., supratidal dolomitization can produce thin, stratified, laterally extensive reservoirs, whereas subsurface fault-controlled dolomitization can produce narrow, linear, vertically extensive reservoirs). Therefore, to predict the spatial distribution of a dolomite reservoir, it is advisable to first determine the process that produced the dolomite. In carbonate

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Contents

AAPG Continuing Education Course Notes Series

Dolomite Reservoirs: Geochemical Techniques for Evaluating Origin and Distribution

J. R. Allan
J. R. Allan
Allan Geological Analysis Fullerton, California, U.S.A.
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W. D. Wiggins
W. D. Wiggins
Chevron Petroleum Technology Company La Habra, California, U.S.A.
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American Association of Petroleum Geologists
Volume
36
ISBN electronic:
9781629810966
Publication date:
January 01, 1993

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