Modeling and experimental study of the effect of pore water velocity on
the spectral induced polarization signature in porous media
Abstract
Induced polarization (IP) is increasingly applied for hydrological,
environmental and agricultural purposes. Interpretation of IP data is
based on understanding the relationship between the IP signature and the
porous media property of interest. Mechanistic models on the IP
phenomenon rely on the Poisson-Nernst-Plank equations, where diffusion
and electromigration fluxes are the driving forces of charge transport
and are directly related to IP. However, to our knowledge, the impact of
advection flux on IP was not investigated experimentally and was not
considered in any IP model. In this work, we measured the spectral IP
(SIP) signature of porous media under varying flow conditions, in
addition to developing and solving a model for SIP signature of porous
media, which takes flow into consideration. The experimental and the
model results demonstrate that as bulk velocity increases, polarization
and relaxation time decrease. Using a numerical model, we established
that fluid flow near the particle deforms the electrical double layer
(EDL) structure, accounting for the observed reduction in polarization.
We found a qualitative agreement between the model and the measurements.
Still, the model overestimates the impact of flow rate on SIP signature,
which we explain in terms of the flow boundary conditions. Overall, our
results demonstrate the sensitivity of the SIP signature to fluid flow,
highlighting the need to consider fluid velocity in the interpretation
of the SIP signature of porous media, and opening an exciting new
direction for noninvasive measurements of fluid flow at the EDL scale.