Temperature dependence of rock salt thermal conductivity: Implications for geothermal exploration

Abstract

Rock salt has high thermal conductivity (>6 W m−1 K−1 at 20 °C) compared to most overlying and adjacent sedimentary rocks, resulting in a thermal blanket effect and a favorable play for low enthalpy geothermal resources. However, the effect of temperature on rock salt thermal conductivity is greater than most other rocks. The result can be a reduction in this contrast between rock types, which has implications for geothermal exploration. The temperature dependence of rock salt thermal conductivity was shown to be a critical factor in our geothermal potential assessment of the Magdalen Islands (Canada). We evaluated the subsurface temperature of this archipelago using numerical simulations of conductive heat transfer, specifying a bulk thermal conductivity of rocks that varies with temperature and porosity, and the latter varying with pressure. A steep geothermal gradient, locally exceeding 40 °C km−1, was found in layers overlying shallow salt domes at depths of ∼1 km but not over a deeper dome due to low thermal conductivity contrasts. This finding highlights the effect of temperature on rock salt thermal conductivity, which should be considered when assessing the geothermal potential of salt domes, intrusions or diapirs, to avoid overestimating the subsurface temperature.