Indirect Electromagnetic Geothermometer--A Novel Approach to the Temperature Estimation in Geothermal Areas

Abstract

The paper presents a review of the advances in the temperature estimation in the geothermal areas based on the recently developed indirect electromagnetic (EM) geothermometer. Unlike other indirect geothermometers, it enables the temperature estimation in the given locations in the earth, which makes it an indispensable tool in geothermal exploration and exploitation. Application of indirect EM geothermometers to the temperature interpolation in the interwell space is discussed. It is shown that the indirect EM geothermometer provides more accurate temperature interpolation in the interwell space than routine mathematical procedures (the relative errors being typically equal to 12% and 30%, accordingly). Special attention is paid to the temperature extrapolation in depth. The results obtained in the northern Tien Shan area indicate that the temperature extrapolation accuracy essentially depends on the distance between the location of the EM sensor at the surface and the borehole where the temperature is to be extrapolated as well as on the ratio between the well length and the extrapolation depth. It is shown that it is possible to increase significantly the deepness of indirect temperature estimation in the earth’s interior based on the available temperature logs. Application of the indirect EM geothermometer in two geothermal areas (Soultz-sous-Forêts, France, and Hengill, Iceland) is presented. The analysis of the appropriate temperature models built using indirect EM geothermometers is used for drawing important conclusions regarding structure of the areas under study; heat sources’ location; the dominating heat transfer mechanisms; fluid circulation paths; and optimal location for drilling geothermal wells.