Universal scaling of the formation factor in clays: Example from the Nankai Trough

Abstract

Electrical conductivity is a fundamental characteristic describing how strongly a network opposes flow of electrical current. In fully water‐saturated porous media the conductivity, represented by the formation factor, is mainly controlled by porosity, connectivity of the conducting phases, and the tortuosity of electrical current paths. Previous work has shown that universal scaling derived from percolation and effective medium theories accurately describes the relationship between formation factor and porosity when the percolation threshold is taken account, as well as the porosity value at which the scaling switches from percolation theory to effective medium theory. We determined the formation factor in clay‐rich sediments based on cation exchange capacity measurements on samples from five scientific ocean drilling sites in the Nankai Trough. We then compared the results to predictions from universal scaling after determining the volume of clay‐bound water and the percolation threshold. We found that the previously reported universal scaling relations hold in these clay‐rich sediments once the corrections are made for the clay‐bound water and that percolation scaling appears to be valid over the entire range of observed porosities, probably due to relatively broad pore size distributions or low pore system connectivity. Our results show that universal scaling can be applied to describe the porosity dependence of the formation factor in clay‐rich sediments when appropriate corrections are made for the presence of clay‐bound water.

A physically based model for the electrical conductivity of water-saturated porous media

“…However, it is seen that the fit at lower fluid conductivity is not as good as at higher one. The reason is that the assumption of the conduction current path in parallel may be not truly valid at low electrolyte concentration [Daigle et al, 2015]. Figure 8 shows the ratio of the electrical conductivity of the glass bead samples to that with ± 10 % uncertainty.…”

Relating Topological and Electrical Properties of Fractured Porous Media: Insights into the Characterization of Rock Fracturing

“…As before, we use the two Archie's law formulations F = φ −m and F = τ /φ. In addition, we consider the percolation-theory model F = (φ − φ c ) −t (e.g., [31,52,53]), in order to evaluate whether the notion of a critical porosity φ c helps to interpret data corresponding to low-porosity fractured porous media with sparse fracture networks. Note that in this case, the estimated value of φ c is restricted to lie between 0 and the minimum porosity of the considered fracture family.…”

Evolution of the Percolation Threshold in Muds and Mudrocks During Burial

“…Thus, it is difficult to predict the relationship between p t and porosity based on the surface area to volume ratio. To this point, both Hunt () and Daigle, Ghanbarian, et al () observed a trend of p t decreasing as porosity decreased in soils and marine muds. A detailed understanding of the phenomena governing these observations is lacking, and yet is critically important for understanding subsurface fluid flow.…”