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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 69 (1985)

Issue: 11. (November)

First Page: 2046

Last Page: 2046

Title: Predictive Models for Sandstone Diagenesis: ABSTRACT

Author(s): Ronald C. Surdam

Article Type: Meeting abstract

Abstract:

The maturation of organic material in hydrocarbon source rocks and inorganic diagenetic reactions in reservoir sandstones are a natural consequence of the burial of a prism of sedimentary rocks. The distribution of porosity/permeability enhancement in potential hydrocarbon reservoirs can be predicted by integrating the reaction processes characterizing the progressive diagenesis of a reservoir/source rock system.

A variety of observations suggests that the organic solvents necessary to increase aluminosilicate and carbonate solubilities in sandstones can be generated either by thermal or oxidative cracking of carbonyl or phenolic groups from kerogen in adjacent source rocks. For example, nuclear magnetic resonance (NMR) spectra of kerogen show that peripheral carbonyl and phenol groups are released from the kerogen molecule prior to the generation of liquid hydrocarbons.

Experimental data indicate that these water-soluble organic solvents can significantly affect the stability of both carbonate and aluminosilicate minerals. Water-soluble organic acids (carboxylic) have been observed in oil field waters in concentrations up to 10,000 ppm, and they commonly dominate the alkalinity in the fluid phase over the 80°-120°C temperature range.

The integration of the organic and inorganic diagenetic reactions can be modeled conceptually by constructing a series of potential reaction pathways with increasing temperature, for a system that includes aluminosilicate minerals, carbonate minerals, organic solvents (carboxylic and phenolic), and carbon dioxide. The important chemical divides in these diagenetic flow diagrams are dependent on temperature, the nature of the buffer in the carbonate system (internal or external), and the relationship between organic acids and PCO2. Forward predictive capabilities result when this general diagenetic model is placed in a time-temperature framework. The detailed organic and inorganic geochemistry and the general thermal scenario used in the time-temperature analysis ust be basin-specific. Casting the diagenetic history of a sandstone into this type of process-oriented model enables one to make the transition from a conventional descriptive mode to a predictive mode of analysis.

Predictive models have been developed for several tectonic settings, including rift or "pull-apart" basins, and intermontane or "Laramide" basins. From these reconstructions, two types of information result: (1) general optimum conditions for porosity/permeability enhancement in sandstones are delineated, and (2) specifically, the degree and potential for porosity/permeability enhancement are determined. Forward prediction of the porosity-enhancing potential of a diagenetic system is possible based on an understanding of the reaction processes in a time-temperature framework.

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Copyright 1997 American Association of Petroleum Geologists