Principle differences in the pressure dependence of thermal and elastic properties of crystalline rocks

Abstract

Thermal conductivity and thermal diffusivity of some metamorphic rocks were measured at room temperature under hydrostatic conditions up to 1000 MPa. For the same rocks the elastic wave velocities were determined up to 500 MPa. The results show two types of behaviour depending on the pressure. At low pressures a strong nonlinear increase of the petrophysical parameters is observed. A transition to a much weaker linear pressure dependence is found at larger pressures. Whereas the low pressure range extends for the elastic properties to pressures up to the order of about 150 MPa, the linear pressure dependence for the thermal parameters is reached at pressures smaller than 50 MPa. The observed difference in the high pressure behaviour is explained with respect to airfilling and scattering centres for phonons and the behaviour of the contacts between the crack faces for elastic wave propagation.