Is it the grain size or the characteristic pore size that controls the induced polarization relaxation time of clean sands and sandstones?

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Abstract
There is a wide range of evidence to suggest that permeability can be constrained through of induced polarization measurements. For clean sands and sandstones, current mechanistic models of induced polarization predict a relationship between the low‐frequency time constant inferred from induced polarization measurements and the grain diameter. A number of observations do, however, disagree with this and indicate that the observed relaxation behavior is rather governed by the so‐called dynamic pore radius Λ. To test this hypothesis, we have developed a set of new scaling relationships, which allow the relaxation time to be computed from the pore size and the permeability to be computed from both the Cole‐Cole time constant and the formation factor. Moreover, these new scaling relationships can be also used to predict the dependence of the Cole‐Cole time constant as a function of the water saturation under unsaturated conditions. Comparative tests of the proposed new relationships with regard to various published experimental results for saturated clean sands and sandstones as well as for partially saturated clean sandstones, do indeed confirm that the dynamic pore radius Λ is a much more reliable indicator of the observed relaxation behavior than grain‐size‐based models.
Funding Information
  • NSF (NSF-EAR-0711053)
  • Swiss National Science Foundation (200021-113363, 200020-125108)

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