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Feldspar alteration and Fe minerals: origin, distribution and implications for sandstone reservoir quality in estuarine sediments

By
Ehsan Daneshvar
Ehsan Daneshvar
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Richard H. Worden
Richard H. Worden
Department of Earth, Ocean and Ecological Sciences, University of Liverpool, 4 Brownlow Street, L69 3GP, UK
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Published:
January 01, 2018

Abstract:

The occurrence and distribution of minerals in modern sedimentary systems hold many clues to help unravel the origin and distribution of reservoir quality-controlling minerals in ancient and deeply buried sandstones, but few quantitative studies have been undertaken. Here we have used a range of techniques including X-ray diffraction, scanning electron microscopy and fully automated mineralogical QEMSCAN analysis to provide a comprehensive understanding of mineral composition and distribution within the post-glacial, clastic sediments of the Ravenglass Estuary, NW England. The Ravenglass Estuary is fed by two main rivers: one drains a granite-dominated hinterland, the other drains a hinterland that contains andesite and Triassic red bed sandstones. The granite-supplied arm has slightly more quartz-rich and Fe mineral-poor sediment than the andesite- and red bed-supplied sediment. The provenance signals are muted for feldspar and mica minerals heavy-mineral garnet populations seem to be sensitive to provenance. Detrital K-feldspar grains are preferentially associated with illite-dominated clay mineral coats, whereas all plagioclase mineral grains are preferentially associated with kaolinite-dominated clay mineral coats. This can be explained by rapid early diagenesis in the sediment with K-feldspar grain surfaces replaced by illite and plagioclase grain surfaces replaced by kaolinite. The andesite- and red bed-supplied sediment contains twice the amount of Fe minerals, which are dominated by chlorite, than the granite-supplied sediment. Chlorite rarely is associated with grain coatings on feldspar grains, possibly because it is predominantly a detrital mineral. Detrital Fe minerals seem to be locally replaced by pyrite due to bacterial sulphate reduction, suggesting that some early diagenetic processes may serve to lock away iron and prevent it from creating Fe-rich clay minerals.

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Geological Society, London, Special Publications

Reservoir Quality of Clastic and Carbonate Rocks: Analysis, Modelling and Prediction

P. J. Armitage
P. J. Armitage
BP Upstream Technology, UK
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A. R. Butcher
A. R. Butcher
Geological Survey of Finland, Finland
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J.M. Churchill
J.M. Churchill
Shell UK Ltd, UK
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A.E. Csoma
A.E. Csoma
MOL Group Exploration, Hungary
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C. Hollis
C. Hollis
University of Manchester, UK
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R. H. Lander
R. H. Lander
Geocosm, USA
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J. E. Omma
J. E. Omma
Rocktype, UK
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R. H. Worden
R. H. Worden
University of Liverpool, UK
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The Geological Society of London
Volume
435
ISBN electronic:
9781786202901
Publication date:
January 01, 2018

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