Comment on: “On the relationship between induced polarization and surface conductivity: Implications for petrophysical interpretation of electrical measurements” (A. Weller, L. Slater, and S. Nordsiek, Geophysics, 78, no. 5, D315–D325)

Abstract

Weller et al. (2013) have recently presented an attempt to connect the surface and quadrature conductivities of porous media using the POLARIS model developed by Revil (2012). This is an important contribution because the development of such a model can be applied in hydrogeophysics and well logging to determine, in a more accurate way, textural properties including the pore size distribution, the porosity, and the permeability of sedimentary rocks. In the last decade, a growing number of researchers have oversold what can be accomplished by resistivity alone, neglecting the effect of surface conductivity. Unfortunately, the paper of Weller et al. (2013) contains inaccurate statements that are discussed below in more detail. Three points deserve a more careful discussion: (1) Weller et al. (2013) argue that the value of the mobility ratio (i.e., the ratio of the mobility of the counterions in the Stern layer by the mobility of the counterions in the diffuse layer) is the same for silicates and aluminosilicates. At the opposite, the POLARIS model (Revil, 2012, 2013a, 2013b) predicts two distinct values for this ratio, one for silicates and one for aluminosilicates. (2) The implications that the mobility ratio is not the same for silica sands and clayey materials may imply that the relationship between the surface conductivity and the quadrature conductivity is not universal. The POLARIS model, at the opposite of what is claimed by Weller et al. (2013), predicts the existence of two distinct trends, one for silicates and one for aluminosilicates. (3) The relationship between surface and quadrature conductivities (both in the paper of Weller et al. [2013] and in the POLARIS model) is also based on another key parameter, the fraction of counterions in the Stern layer f (also known as the partition coefficient in POLARIS). According to Weller et al. (2013), f should …