A SIMPLE METHOD TO DETERMINE HEAT-PRODUCTION FROM GAMMA-RAY LOGS

Usually the radiogenic heat production is determined from the potassiu m (K), uranium (U) and thorium (Th) content and the rock density by us ing the formula by Rybach (1986). In boreholes, the K, U and Th conten t can be taken from the Natural Gamma Spectrometry Tool (NGS) measurem ents and the rock density from the Lithe Density Tool (LDT) measuremen ts. In this paper a simple method is presented to determine heat produ ction from normal gamma ray logs which are readily available from a va st 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 a mphibolite 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 erro r lower than 10%. Reliable information of the radiogenic heat producti on for the use in thermal modelling now can be derived quickly using o nly standard GR (API) readings. (C) 1996 Elsevier Science Ltd.