--> Abstract: Tight Gas Sandstones: Inhibition of Illite Growth By Export of Potassium Into Adjacent Shales?, by Reinhard Gaupp, Svenja Waldmann, Robert Schöner, Anton Irmen, Antony J. Park, and Horst Zwingmann; #90082 (2008)

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Tight Gas Sandstones: Inhibition of Illite Growth By Export of Potassium Into Adjacent Shales?

Reinhard Gaupp1, Svenja Waldmann1, Robert Schöner1, Anton Irmen2, Antony J. Park4, and Horst Zwingmann3
1Earth Sciences, University of Jena, Jena, Germany
2Gaz de France Production Exploration Germany, Lingen, Germany
3CSIRO Petroleum, Perth, Perth, WA, Australia
4Sienna Geodynamics & Consulting Inc., Bloomington, IN

Illite growth within poresystems of deeply buried sandstones is a major factor of reservoir quality deterioration. In reservoir volumes with extensive illitisation, individual layers or shale-sand intercalations stand out with only minor or lacking illite growth. Although there are several possible reasons to be invoked for illite-free layers surrounded by illitised intervals, the processes causing this condition remain enigmatic.

We want to test the hypothesis, that sandstone-shale couplets can be treated as open-systems with ion exchange from sand to shale and vice versa. Feldspar in sandstones is the major K+ source for the illitisation of illite-smectite mixed-layer minerals in nearby shales. The K+ from feldspar dissolution in sandstone layers is diffusively transported into adjacent shales. The export and consumption of K+ prevents the illite precipitation in the sandstones. In shales adjacent to sandstones we expect higher K-contents with decreasing trend away from the sandstone-shale contact, illite crystallinity and K/Ar-age trends within shales.
With a comparative investigation of sandstone-shale couplets we test the working hypothesis with mineralogical, petrographical, (isotope-) geochemical methods of high spatial resolution and modelling of diffusive mass-transfer processes.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery