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Thermogravimetry/evolved water analysis (TG/EWA) combined with XRD for improved quantitative whole-rock analysis of clay minerals in sandstones

Published online by Cambridge University Press:  09 July 2018

D. M. Thornley  and
T. J. Primmer
D. M. Thornley
Affiliation:
BP Exploration, Research and Engineering Centre, Chertsey RdSunbury-on-Thames, Middx, TW16 7LN, UK
T. J. Primmer
Affiliation:
BP Exploration, Research and Engineering Centre, Chertsey RdSunbury-on-Thames, Middx, TW16 7LN, UK
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Abstract

Current methods of quantitative whole-rock clay mineral analysis of sandstones often provide little more than an estimate of clay mineral abundances, especially where the total clay mineral content is <10 wt% of the sandstone. More accurate determinations of clay mineral abundance in the whole rock can be made by combining thermogravimetry/evolved water analysis (TG/EWA) and X-ray diffraction (XRD) data. The TGA/EWA system incorporates a purpose built thermobalance linked to a water specific infrared detector which is used to measure quantitatively the clay mineral dehydroxylation water evolved from the whole rock when heated from 250°C to 900°C. This gives a measure of the total hydroxyl content of the clay minerals in the whole rock which, when combined with XRD analysis of a separated clay size-fraction, enables individual clay mineral abundances in the whole-rock sample to be determined. Results on artificial sand/clay mineral mixtures prepared with known amounts of different clay minerals (chlorite, illite and kaolinite) show that the accuracy of the combined method is most influenced by the accuracy of the XRD data. Errors associated with TG/EWA were found to be negligible by comparison. A case study is included in which the technique has been used to determine accurately the illite abundance in the Magnus Sandstone Reservoir, Northern North Sea.

Type
Research Article
Information
Clay Minerals , Volume 30 , Issue 1 , March 1995 , pp. 27 - 38
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1995

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