Nuclear techniques in the evaluation of geothermal resources

Nuclear techniques are employed in exploration, development and monitoring of production of geothermal resources. An understanding of the relationships between heat flow and heat production in a region depends on the knowledge of natural radio-element contents of crustal materials. These contents are most readily determined by field and laboratory gamma-spectrometric methods. Radio-element contents of hot spring systems and produced geothermal fluids are also determined by gamma spectrometry, as well as by alpha-spectrometric and neutron activation analyses. Contents of major and trace elements, some of which are used as the bases for chemical geothermometers, are analysed by X-ray fluorescence and neutron activation. Mass spectrometric techniques are employed to determine oxygen and hydrogen isotopic ratios, and abundances and ratios of noble gases in geothermal fluids. Anomalous contents of soil-gas mercury, a potential indicator of hydrothermal circulation, may be detected in the field by atomic absorption equipment. As in petroleum and mineral exploration, drilling for geothermal resources is guided and evaluated by subsurface logging, utilizing nuclear techniques. (author)