Isotope geothermometry in the larderello geothermal field

Abstract

The isotope geothermometers based on the 13C/ 12C fractionation between carbon dioxide and methane and on the 18O/ 16O fractionation between carbon dioxide and water vapour have been applied in Larderello geothermal field. The CO 2 - CH 4 thermometer gives temperatures which are 50–200°C higher than those measured at the well head. The distribution of the isotopic temperatures within the field follows more or less similar patterns to those given by the well-head temperatures. They are believed to reflect the temperatures of formation of CO 2 and CH 4. The CO 2 - H 2O thermometer gives the temperature of the geothermal reservoirs tapped, and the difference between the isotopic temperature and the temperature measured at the well head is a measure of the cooling undergone by geothermal fluid on its way up to the surface.