Thermal diffusivity measurements at NGU - Status and method development 2005-2008

Abstract

NGUs equipment for measuring thermal diffusivity of rock samples is based on Middleton (1993). Thermal conductivity is calculated as a product of density, specific heat capacity and thermal diffusivity. During the period from spring 2005 to the present day, a series of tests and analyses had been performed to: (1) increase our understanding of the thermal processes occurring during testing, and (2) to improve NGU's routines and reproducibility. There still remains significant scope for improvement.\rDetermination of the thermal properties of rock samples from Norwegian bedrock is not straightforward. The material is inhomogeneous and anisotropic; properties may vary over a scale of centimetres and according to sample orientation. With this in mind, in order to obtain a reasonable understanding of the thermal conductivity distribution, either at depth in a cored borehole or near the bedrock surface, the number of analysed samples is a critical factor. Thus, many samples with \"adequate\" analytical quality might be preferable to relatively few samples analysed with high accuracy. (...)