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Clay mineral distribution in the Devonian-Carboniferous sandstones of the Clair Field, west of Shetland, and its significance for reservoir quality

Published online by Cambridge University Press:  09 July 2018

M. D. Pay ,
T. R. Astin  and
A. Parker
M. D. Pay*
Affiliation:
Postgraduate Research Institute for Sedimentology, University of Reading, PO Box 227, Whiteknights, Reading RG6 6AB, UK
T. R. Astin
Affiliation:
Postgraduate Research Institute for Sedimentology, University of Reading, PO Box 227, Whiteknights, Reading RG6 6AB, UK
A. Parker
Affiliation:
Postgraduate Research Institute for Sedimentology, University of Reading, PO Box 227, Whiteknights, Reading RG6 6AB, UK
*
*E-mail: mark.pay@london.entoil.com
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Abstract

The Devonian-Carboniferous reservoir of the Clair Field contains a complex and variably abundant clay mineral assemblage. An abrupt vertical change in clay mineralogy has been observed in both wells studied (UKCS 206/8-7 and 206/8-8) from being rich in Mg-chlorite, chlorite- smectite (including dioctahedral corrensite), illite, illite-smectite and Fe-chlorite, to being smectite- rich. This change broadly coincides with the unconformable boundary between the Lower Clair Group and Upper Clair Group of the reservoir which possibly defines the Devonian-Carboniferous boundary. The clay minerals present reflect interaction between: (1) tectonic stability and climate that controlled the detrital composition of the sediment; (2) the pore-waters that developed; and (3) the result of diagenetic modification.

Matrix porosity and permeability is severely restricted where the pore-lining clays are abundant (>15%) and where the clays bridge or fill pores. The type of clay mineral species appears to have a minor influence on reservoir quality, although they may be extremely important during production. The best reservoir quality occurs in mature aeolian sediments with a thin illite and illite-smectite clay coating.

Keywords

clay mineralsClair FieldShetlandreservoir quality
Type
Research Article
Information
Clay Minerals , Volume 35 , Issue 1 , March 2000 , pp. 151 - 162
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2000

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Footnotes

†

Present address: Enterprise Oil plc, Grand Buildings, Trafalgar Square, London WC2N 5EJ, UK

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