Effect of temperature and pressure on the thermal conductivity of sandstone

Effective thermal conductivity (ETC) of dry sandstone was measured over a temperature range from 275 to 523 K and at pressures up to 400 MPa with a guarded parallel-plate apparatus. The estimated uncertainty of the ETC measurements is 2%. The porosity of the sample was 13%. A rapid increase of ETC was found for dry sandstone at low pressures between 0.1 and 100 MPa along various isotherms. At high-pressure range (P>100 MPa) a weak linear dependence of the ETC with pressure was observed. The pressure effect is negligibly small after first 80–100 MPa where bridging of microcracks or improvement of grain contacts takes place. We interpreted the measured ETC data using a various theoretical and semi-empirical models in order to check their accuracy and predictive capability. The effect of structure (size, shape, and distribution of the pores), porosity, and mineralogical composition on temperature and pressure dependences of the ETC of sandstone was discussed. To estimate the effect of temperature and pressure on the ETC of sandstone the pressure, β_P, and temperature, β_T, coefficients of ETC were calculated from the measured values of ETC. The measured values of the ETC were also used to calculate the values of the isothermal compressibility, χ_T, and thermal expansion coefficient, α. The equation of state of sandstone was developed using the measured ETC data.