Thermal conductivity of selected claystones and mudstones from England

The claystones and mudstones investigated are London Clay, Fullers Earth, Oxford Clay and Kimmeridge Clay. The thermal conductivities were measured using a divided bar apparatus and the values measured perpendicular to layering ranged from 0.68 to 0.97 W/mK. Comparative measurements of thermal conductivities were carried out by the needle probe method and Middleton's method. Deviations of up to 50% were obtained between the needle probe and the divided bar method. The thermal conductivities estimated from the geometric mean model based on mineralogy and water content ranged from 0.87 to 2.01 W/mK, considerably higher than the measured values. A correlation was found between the grain size distributions of the samples and the measured thermal conductivities. This textural effect on the thermal conductivity is assumed to be the main reason for the low measured values and the lack of correlation between the measured and the calculated values.