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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 2. (February)

First Page: 311

Last Page: 311

Title: Nature of Secondary Porosity Created by Dissolution of Aluminum Silicates: ABSTRACT

Author(s): Alan Thomson, R. K. Stoessell

Article Type: Meeting abstract


Porosity enhancement in sandstone reservoirs cannot be due to dissolution of aluminum silicates without implying aluminum mobility. However, aluminum has yet to be reported in reservoir fluids at greater than trace concentrations. Predicted aqueous aluminum concentrations in subsurface fluids approach a level that Curtis has termed "a good approximation of zero."

Several studies of secondary pore systems formed by aluminum silicate dissolution demonstrate that aluminum is conserved on a scale of a few inches, in the form of diagenetic clay minerals--notably kaolinite. Our examinations indicate that the products of dissolution of aluminum silicate grains (which include feldspar and many rock fragments) can be accounted for in thin section primarily by the presence of adjacent pore-filling kaolinite and possibly authigenic quartz and albite. At high temperatures, the diagenetic mineral is often illite.

Secondary porosity formed by dissolution of aluminum silicate grains should not necessarily be construed as adding to total porosity, but should rather be thought of as a "rearrangement" of porosity already present. Indeed, the process may actually be harmful, inasmuch as the newly formed clay minerals can greatly reduce permeability. Calcite resorption remains the principal means of adding to total porosity through a dissolution process.

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Copyright 1997 American Association of Petroleum Geologists