Electrode effects and electrical non-linear behavior in rocks.

Abstract

Previous studies on rocks saturated with electrolyte have shown electrical linear behavior up to a cunent density limit; above such a limit non-linearities appear. Evidence was obtained of the opposite behavior in some "dry" resistive rocks in contact with metallic electrodes. It shows the existence of a non-linear region followed by a linear one when the voltage, or current density, is increased. Experimental evidence of charge concentrations in the metallic electrodes vicinity is related to non-linear phenomena at low voltages. A conduction model based on transient responses of a hematitic sandstone-In Hg system identifies two groups of charge carriers. One group is characterized by a fast relaxation mechanism that appears to be associated with Surface conduction, the other is associated with low-mobility carriers apparently moving through the rock matrix.