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Diagenetic influences on reservoir properties of the Sherwood Sandstone (Triassic) in the Marchwood geothermal borehole, Southampton, UK

Published online by Cambridge University Press:  09 July 2018

R. W. O'B. Knox
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG
W. G. Burgess
Affiliation:
Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OXI0 8BB
K. S. Wilson
Affiliation:
Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OXI0 8BB
A. H. Bath
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG

Abstract

Petrological studies of the Sherwood Sandstone of the Marchwood Borehole show that the formation is made up of two units of differing primary lithological character: a lower unit with lithic sandstone and conglomerate, and an upper unit with arkosic sandstone. A combination of compaction and calcite cementation (early and late) has severely reduced porosity and permeability in the lower unit. In the upper unit compaction is again important, but several beds have largely escaped cementation, and their primary porosity has been enhanced by leaching of feldspars. The secondary porosity reaches 7% in some samples. Oxygen and carbon isotope data for the early (calcrete) cements indicate isotopic equilibrium with typical freshwater compositions. The later cements yield more variable values, indicating precipitation under a wider range of conditions.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1984

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