A study of the effects of pore-water salinity on some physical properties of sedimentary rocks at permafrost temperatures

Abstract

The effect of pore-water salinity on the elastic wave velocities and electrical resistivities of frozen, saturated specimens of two sandstones and a limestone have been studied in the temperature range −15 to +4 °C. The specimens were saturated with solutions whose salinities varied from 0.0 M (distilled water) to 1.0 M NaCl.An increase in pore-water salinity reduces the effect of sharp increases in velocity as the temperature is reduced below 0 °C. The ratio of compressional to shear-wave velocities shows a weak dependence on temperature and salinity. Calculations of the ice content showed that the pore spaces were not completely filled with ice, even at the lowest temperature (−15 °C) reached.An increase in either temperature or salinity was found to lower the complex resistivity, and to extend the range of frequency over which the resistive behavior, rather than the dielectric, was dominant. The decrease in resistivity was observed to be most rapid when the pore water salinity was increased from 0.0–0.3 M. The ratio of the resistivity of a rock when frozen (ρf) to that when thawed (ρt) can be shown to be related to the fraction (Sw) of the water remaining unfrozen at subzero temperatures by ρf/ρt = (Sw)1−n. By combining the results of the velocity and resistivity measurements, it was found that n = 0.9 log pf/pt + 2.3.