Any prediction of sub-surface temperatures, or evaluation of heat flow from measured temperatures, requires knowledge of the thermal conductivities of the rocks in the area under consideration. An accurate evaluation of the thermal conductivity of mudstones is particularly important, not only because of their widespread occurrence in sedimentary basins but also because of their relatively high insulating effect.

The difficulties in making thermal conductivity measurements of mudstones and the methods used are briefly discussed.

A simple expression for a relationship between thermal conductivity, density and lithology is derived from physical considerations and verified by experiment. The importance of this relationship for geothermal studies in uncored wells is discussed (mudstone sections are rarely cored in commercial holes).

Finally, a table of values of thermal conductivities of mudstones, of Triassic to Pleistocene age, from the Hampshire and Lincolnshire basins and from the Moray Firth, are presented. These values range from l.2 Wm-1K-1 for the Pleistocene clays in the Moray Firth to 2.3 Wm-1 K-1 for the Keuper Marl in the Hampshire Basin.

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