The specific surface of particles' and the properties of the pore fluid control the sensitivity of shales to a given change in the host environment. In this study, dielectric permittivity measurements are suggested to assess the reactivity coefficient, which is a measure of the physico-chemical sensitivity of a clay-fluid system. The effects of specific surface and pore fluid properties on permittivity data are discussed using dielectric spectra of ideal systems and real shale cores. Normalized high-frequency real permittivity data and the percentage of free water (estimated using high- frequency imaginary permitivity spectra) are shown to decrease with the increase in the reactivity coefficient. Similarly, high low-frequency permittivity values normal to the bedding plane indicate systems with high reactivity coefficients. Vertical strains measured during osmotic consolidation tests confirm the previous trend. Finally, general guidelines are presented to help in identification of reactive systems using complex permiflivity measurements.

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