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Parametric study of the physical properties of hydrate-bearing sand, silt, and clay sediments: 1. Electromagnetic properties

Journal of Geophysical Research

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Abstract

The marked decrease in bulk electrical conductivity of sediments in the presence of gas hydrates has been used to interpret borehole electrical resistivity logs and, to a lesser extent, the results of controlled source electromagnetic surveys to constrain the spatial distribution and predicted concentration of gas hydrate in natural settings. Until now, an exhaustive laboratory data set that could be used to assess the impact of gas hydrate on the electromagnetic properties of different soils (sand, silt, and clay) at different effective stress and with different saturations of hydrate has been lacking. The laboratory results reported here are obtained using a standard geotechnical cell and the hydrate-formed tetrahydrofuran (THF), a liquid that is fully miscible in water and able to produce closely controlled saturations of hydrate from dissolved phase. Both permittivity and electrical conductivity are good indicators of the volume fraction of free water in the sediment, which is in turn dependent on hydrate saturation. Permittivity in the microwave frequency range is particularly predictive of free water content since it is barely affected by ionic concentration, pore structure, and surface conduction. Electrical conductivity (or resistivity) is less reliable for constraining water content or hydrate saturation: In addition to fluid-filled porosity, other factors, such as the ionic concentration of the pore fluid and possibly other conduction effects (e.g., surface conduction in high specific surface soils having low conductivity pore fluid), also influence electrical conductivity.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Parametric study of the physical properties of hydrate-bearing sand, silt, and clay sediments: 1. Electromagnetic properties
Series title:
Journal of Geophysical Research
Volume
115
Issue:
B11104
Year Published:
2010
Language:
English
Publisher:
American Geophysical Union
Publisher location:
Washington, D.C.
Contributing office(s):
Woods Hole Coastal and Marine Science Center
Description:
9 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Number of Pages:
35