About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 73 (1989)

Issue: 4. (April)

First Page: 472

Last Page: 482

Title: Burial Diagenesis and Specific Catalytic Activity of Illite-Smectite Clays from Vienna Basin, Austria

Author(s): W. D. Johns (2), T. E. McKallip (2)

Abstract:

A sequence of Tertiary shales from the Vienna basin, Austria, contains a series of illite-smectite (I/S) clays that are the source of catalytic activity as measured by the method developed by Goldstein in 1983. The source of this activity is Bronsted acidity resulting from the dissociation of water molecules bonded to exchangeable cations in the interlayers of the smectite and on the external basal surfaces of illite platelets. This specific catalytic activity (SCA) is exchangeable cation dependent and correlates directly with increasing interlayer charge and tetrahedral substitution accompanying the diagenetic formation of thin interlayer illite particles with high-charge external surfaces. As a result, diagenetic transformation of smectite to illite in this series resul s in increased catalytic activity. From consideration of cation exchange capacity and interlayer charge of end-member components of this I/S series, we show that a cation site resulting from tetrahedral substitution of Al3+ for Si4+ has an activity about 40 times greater than a site of octahedral origin. The end-member illite particles of this I/S series have calculated mean thicknesses of about 80A (eight 2:1 mica layers). The linear relationship between SCA values and estimated platelet thickness for three different micas and illites confirms the role of cation sites on external basal surfaces as sources of catalytic activity.

The possibility of direct involvement of catalytically active diagenetic illite in natural kerogen pyrolysis, acting simultaneously with a fluid release mechanism and its geopressure development, may provide optimum conditions for hydrocarbon generation and migration during I/S diagenesis. The presence of high-surface-area illite in diagenetically altered reservoir sandstones suggests the possibility for modifying the hydrocarbon constitution of crude oils within buried reservoirs. The effects of exchange cation composition on catalytic properties of I/S clays show that formation water chemistry must be considered in evaluating the effectiveness of clay catalysts in hydrocarbon-forming reactions.

Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Watermarked PDF Document: $14
Open PDF Document: $24

AAPG Member?

Please login with your Member username and password.

Members of AAPG receive access to the full AAPG Bulletin Archives as part of their membership. For more information, contact the AAPG Membership Department at [email protected].