A simple method to determine heat production from gamma-ray logs

Usually the radiogenic heat production is determined from the potassium (K), uranium (U) and thorium (Th) content and the rock density by using the formula by Rybach (1986). In boreholes, the K, U and Th content can be taken from the Natural Gamma Spectrometry Tool (NGS) measurements and the rock density from the Lithe Density Tool (LDT) measurements. In this paper a simple method is presented to determine heat production from normal gamma ray logs which are readily available from a vast number of boreholes. This method is based on a linear relationship between the gamma ray GR and the heat production A. For a wide variety of lithologies extending from granite through gneiss, carbonate and amphibolite to basaltic rocks, it is shown, that this relation is valid in the range 0-350 API and 0.03-7 mu W/m(3) respectively with an error lower than 10%. Reliable information of the radiogenic heat production for the use in thermal modelling now can be derived quickly using only standard GR (API) readings. (C) 1996 Elsevier Science Ltd.