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Observations of heterogeneous pore pressure distributions in clay-rich materials

Published online by Cambridge University Press:  05 July 2018

R. J. Cuss ,
J. F. Harrington ,
C. C. Graham ,
S. Sathar  and
A. E. Milodowski
R. J. Cuss*
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
J. F. Harrington
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
C. C. Graham
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
S. Sathar
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
A. E. Milodowski
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
*
*E-mail: [email protected]
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Abstract

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The concept of effective stress is one of the basic tenets of rock mechanics where the stress acting on a rock can be viewed as the total stress minus the pore water pressure. In many materials, including clay-rich rocks, this relationship has been seen to be imperfect and a coefficient (χ) is added to account for the mechanical properties of the clay matrix. Recent experimental results during the flow testing (both gas and water) of several rocks (Callovo-Oxfordian claystone, Opalinus Clay, Boom Clay) and geomaterials (bentonite, kaolinite) has given evidence for stable high pressure differentials. The design of the experiments allows multiple measurements of pore pressure, which commonly shows a complex distribution for several different experimental geometries. The observed stable high pressure differentials and heterogeneous pore pressure distribution makes the describing of stress states in terms of effective stress complex. Highly localized pore pressures can be sustained by argillaceous materials and concepts of evenly distributed pore pressures throughout the sample (i.e. conventional effective stress) do not fit many clay-rich rocks if the complexities observed on the micro-scale are not incorporated, especially when considering the case of gas flow.

Keywords

bentonitecallovo-oxfordian claystonekaoliniteopalinus claypressuremechanical propertiesargillaceous rockseffective stress
Type
Research Article
Information
Mineralogical Magazine , Volume 76 , Issue 8 , December 2012 , pp. 3115 - 3129
Creative Commons
Creative Common License - CCCreative Common License - BY
© [2012] The Mineralogical Society of Great Britain and Ireland. This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY) licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2012

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