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Book Chapter

The importance of illitic minerals in shale instability and in unconventional hydrocarbon reservoirs

By
M. J. Wilson
M. J. Wilson
1
James Hutton Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
2
Department of Geology and Minerals Prospecting, Geology & Petroleum Engineering Institute, Tomsk Polytechnic University, Tomsk 634050, Russia
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L. Wilson
L. Wilson
1
James Hutton Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
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M. V. Shaldybin
M. V. Shaldybin
2
Department of Geology and Minerals Prospecting, Geology & Petroleum Engineering Institute, Tomsk Polytechnic University, Tomsk 634050, Russia
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Published:
January 01, 2017

Abstract

It is generally accepted that the clay mineralogy of the shale formation is a primary causative factor of shale instability. This review considers a scenario of shale instability relating to illitic minerals. From the literature the thickness of the double electric layer (DEL) of the aqueous solutions associated with the charged external surfaces of clay minerals is of the same order or even thicker than the sizes of a significant proportion of the pores found in shales. In these circumstances, overlap of the DELs associated with the exposed outer surfaces of clay minerals on opposing sides of slit-like micropores (<2 nm in diameter) and mesopores (2–50 nm in diameter) in a lithostatically compressed shale would bring about electrostatic repulsion and lead to increased pore/hydration pressure in illitic shales. In shales and sandstones, illitic material is usually described in terms of two different phases, namely illite per se and mixed-layer illite–smectite (I/S). Evidence is presented to show that it is often the case that only one illite phase exists and that in reality the mixed-layer I/S is simply very thin illite (<5 nm in thickness) in the early stages of its growth. Such material is of common occurrence in the unconventional hydrocarbon reservoirs of the USA.

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Contents

Geological Society, London, Special Publications

Geomechanical and Petrophysical Properties of Mudrocks

E. H. Rutter
E. H. Rutter
University of Manchester, UK
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J. Mecklenburgh
J. Mecklenburgh
University of Manchester, UK
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K. Taylor
K. Taylor
University of Manchester, UK
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Geological Society of London
Volume
454
ISBN electronic:
978-1-78620-335-9
Publication date:
January 01, 2017

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