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Porosity Prediction in Shallow Versus Deep Water Limestones- Primary Porosity Preservation Under Burial Conditions

By
Peter A. Scholle
Peter A. Scholle
U.S. Geological Survey
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Published:
January 01, 1979

Abstract

Preservation of primary porosity is an important factor in many oil and gas fields producing from carbonate rocks. Initial porosities in the range of 30–40% (in grainstones) and 60–75% (in mudstones) are common in carbonate sediments and under a number of circumstances much of this primary porosity can be preserved. However, many factors such as early cementation, compaction, stylolitization and subsurface cementation tend to reduce primary porosity. Thus, we must understand and be able to predict the effects of a variety of diagenetic processes before we can effectively explain the distribution of preserved primary porosity.

Prediction of preserved primary porosity in carbonate rocks is at best a difficult undertaking. Most carbonate hydrocarbon reservoirs drilled have been in shallow-water limestones. In such rocks, depositional patterns are complex and variable, and diagenetic alteration of original sediment textures and compositions may be extreme. Few, if any, general rules can be used to predict the porosity of such carbonate rocks in the absence of drilling data. Even where a significant number of wells have been drilled, useful porosity trends that enable accurate porosity prognostication over even relatively short distances may be difficult to discern.

Deep-water limestones, on the other hand, generally have much more predictable porosity. They have more uniform depositional facies, more predictable primary chemical compositions, and simpler diagenetic alteration patterns than their shallow-water equivalents. Alteration of deep-water limestones is controlled mainly by their maximum burial depth. Average rates for such diagenetic porosity loss can be determined as a function of burial.

Deep-water

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Contents

AAPG Continuing Education Course Notes Series

Geology of Carbonate Porosity

Don Bebout
Don Bebout
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Graham Davies
Graham Davies
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Clyde H. Moore
Clyde H. Moore
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Peter S. Scholle
Peter S. Scholle
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Norman C. Wardlaw
Norman C. Wardlaw
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American Association of Petroleum Geologists
Volume
11
ISBN electronic:
9781629811888
Publication date:
January 01, 1979

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