Permeability estimation from induced polarization: an evaluation of geophysical length scales using an effective hydraulic radius concept

Andreas Weller,Lee Slater

doi:10.1002/nsg.12071

Abstract

ABSTRACTGeophysical length scales defined from induced‐polarization measurements can be used in models of permeability (k) prediction. We explore the relative merit of different induced‐polarization parameters as proxies of an effective hydraulic radius (reff) that can be used to predict permeability from a modified Hagen–Poiseuille equation. Whereas geometrical measures of the hydraulic radius are good proxies of reff, the induced‐polarization measures are not well correlated with reff. However, a new proxy of reff that considers both imaginary conductivity and formation factor shows an improved correlation with reff. The resulting model enables a better quality of permeability prediction compared with the other geophysical length scales, but does not reach the predictive quality of the models based on geometrical length scales. The specific polarizability defined when incorporating the effect of the formation factor on imaginary conductivity appears to be independent of pore geometry, indicating that it is the correct parameter representing the role of the surface electrochemistry on the induced‐polarization effect. However, the joint dependence of induced‐polarization measurements on both the pore radius and the tortuosity and porosity of the interconnected pore network is a limitation to the widely explored use of induced‐polarization measurements to isolate surface properties from volumetric properties of the interconnected pore network.

Highlights

Induced polarization (IP) is an electrical geophysical prospecting method that records the space charge polarization of ions in the electrical double layer (EDL) forming at the grain–fluid interface
Geophysical length scales have been defined from two pieces of information extractable from IP data sets: (1) a measure of the dominant relaxation time of the polarization, which is closely related to the dominant pore size of the porous network controlling fluid flow in soil/rock (e.g. Scott and Barker 2003) and (2) a measure of the total strength of the polarization, which is closely related to the total interfacial surface area of the interconnected pore space (e.g. Weller et al 2010b)
We further evaluate the merit of the concept of geophysical length scales for k estimation discussed by Robinson et al (2018) through a comparison against an effective hydraulic radius that can be directly calculated from the Hagen–Poiseuille equation describing a bundle of capillaries

Summary

Introduction

Induced polarization (IP) is an electrical geophysical prospecting method that records the space charge polarization of ions in the electrical double layer (EDL) forming at the grain–fluid interface. The measurements have proven sensitivity to the pore geometry controlling fluid flow Scott and Barker 2003; Weller et al 2010b). Geophysical length scales have been defined from two pieces of information extractable from IP data sets: (1) a measure of the dominant relaxation time of the polarization, which is closely related to the dominant pore size of the porous network controlling fluid flow in soil/rock Scott and Barker 2003) and (2) a measure of the total strength of the polarization, which is closely related to the total interfacial surface area of the interconnected pore space (e.g. Weller et al 2010b). Near Surface Geophysics published by John Wiley & Sons Ltd on behalf of European Association of Geoscientists and Engineers

Methods

Results

Discussion

Conclusion