TEMPERATURE-DEPENDENCE OF THE ELECTRICAL-RESISTIVITY OF WATER-SATURATED ROCKS

The electrical resistivities of several dacitic tuffs, sandstone, andesite, granite, and crystalline limestone samples saturated with a 0.001 M aqueous solution of KCl, were measured in the range from room temperature to 250°C. Basically the samples used in the present study show a quasi-exponential decrease of resistivity with temperature up to 200°C. The same temperature dependence is found for the resistivity of the saturating solution, thus confirming that conduction in water-saturated rocks is essentially electrolytic. At temperatures above 200°C, some specimens of highly porous dacitic tuff still closely follow the saturating solution in the pattern of resistivity variation with temperature, exhibiting a minimum around 220°C; however, the behavior of low-porosity crystalline rocks (notably granite) where a relatively abrupt decrease of resistivity is observed above 50°C, departs from that of the saturating solution. This experimental evidence points out that mechanisms different from water characteristics, such as growth of microcracks or chemical reactions, contribute to electrical conduction at high temperature. -from Authors