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Water Resources Research

Stress induced permeability anisotropy of Resedimented Boston Blue Clay

Authors

  • Amy L. Adams,

    Corresponding author
    1. Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
    • Corresponding author: A. L. Adams, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Rm 1–353, 77 Massachusetts Ave., Cambridge, MA 02139, USA. (aadams@mit.edu)

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  • John T. Germaine,

    1. Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
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  • Peter B. Flemings,

    1. Jackson School of Geosciences, University of Texas at Austin, Austin, Texas, USA
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  • Ruarri J. Day-Stirrat

    1. Bureau of Economic Geology, University of Texas at Austin, Austin, Texas, USA
    2. Now at Shell International Exploration and Production, Projects and Technology, Houston, Texas, USA
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Abstract

[1] In Resedimented Boston Blue Clay (RBBC), a low-plasticity glacio-marine illitic mudrock, the ratio of the horizontal to vertical permeability (the permeability anisotropy, rk) increases from 1.2 to 1.9 as the porosity decreases from 0.5 to 0.37 and the permeability decreases by more than 1 order of magnitude. Backscattered Scanning Electron Microscope (BSEM) images taken at formation stress levels reveal that particles rotate perpendicular to the axial loading direction by ∼22°, with larger particles rotating more significantly and achieving more uniform alignment than smaller particles. We show experimentally that preferred platy particle orientation can explain our permeability anisotropy measurements. The permeability anisotropy of mechanically compressed mudrocks is minimal, <2.5. We use a novel approach (cubic specimens) to measure the evolution of permeability anisotropy in different directions on the same specimen, unlike most other methods. Modified analytic techniques allow calculation of the permeability anisotropy for a specimen using directional constant head permeability methods. A better understanding of the evolution of permeability anisotropy during sediment burial is important for modeling subsurface transport processes, including hydrocarbon migration and contaminant transport, as well as estimating in situ conditions such as pore pressure, overpressure, and effective stress.

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