Characterization of rock thermal conductivity by high-resolution optical scanning

We compared three laboratory methods for thermal conductivity measurements] divided! bar\ line!source and optical scanning[ These methods are widely used in geothermal and petrophysical studies\ particularly as applied to research on cores from deep scienti_c boreholes[ The relatively new optical scanning method has recently been perfected and applied to geo! physical problems[ A comparison among these methods for determining the thermal con! ductivity tensor for anisotropic rocks is based on a representative collection of 79 crystalline rock samples from the KTB continental deep borehole "Germany#[ Despite substantial thermal inhomogeneity of rock thermal conductivity "up to 39 49) variation# and high anisotropy "with ratios of principal values attaining 1 and more#\ the results of measurements agree very well among the di}erent methods[ The discrepancy for measurements along the foliation is negligible " 0)#[ The component of thermal conductivity normal to the foliation reveals somewhat larger di}erences "2 3)#[ Optical scanning allowed us to characterize the thermal inhomogeneity of rocks and to identify a three!dimensional anisotropy in thermal conductivity of some gneiss samples[ The merits of optical scanning include minor random errors "0[5)#the ability to record the variation of thermal conductivity along the sample\ the ability to sample deeply using a slow scanning rate\ freedom from constraints for sample size and shapeand quality of mechanical treatment of the sample surface\ a contactless mode of measurementhigh speed of operation\ and the ability to measure on a cylindrical sample surface[ More traditional methods remain superior for characterizing bulk conductivity at elevated tempera! ture[ 0888 CNR[ Published by Elsevier Science Ltd[ All rights reserved[