Salinity dependence of the thermoelectric coupling coefficient in brine-saturated sandstones

We report measurements of the thermoelectric coupling coefficient in intact sandstone samples saturated with NaCl brine at concentrations ranging from 1 × 10^-4 to 1 M. Our measurements account for temperature-dependent electrode effects. We also present a model for the salinity dependence of the thermoelectric coupling coefficient which yields a close match to the experimental data. At low salinity, the measured coupling coefficient exhibits the salinity dependence predicted for a perfect membrane, while at high salinity, the coupling coefficient follows that predicted for an uncharged porous medium. Measured values of the coupling coefficient range from 0.370 mVK^-1 at low salinity (1 × 10^-4 M), to 0.055 mVK^-1 at high salinity (1 M).