Exploration for geothermal energy requires reevaluation of existing exploration techniques and development of new ones.

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The suites of techniques being employed in geothermal exploration are different from those in either mineral or petroleum exploration.

Geologic reconnaissance techniques involve the mapping of hot springs, fumaroles, and volcanoes. Plate margins typically delineate the broader zones in which economic geothermal reservoirs may occur. Empirical correlation exists between the rate, the angle of subduction, and the spatial occurrence of active volcanoes providing a general guide for exploration. Andesites are more commonly associated with productive geothermal fields than are the more basic rocks.

Geochemical thermometry, coupled with hydrogeologic studies, provides useful clues as to the probable last equilibrium temperature of geothermal reservoirs. However, dilution and continuous rock-water interaction often obfuscates the true reservoir temperature.

Geophysical techniques have become indispensable in narrowing down the targets to be tested by drilling. Foremost among the geophysical techniques is the electrical resistivity method and all of its variants, including deep electromagnetic soundings, tellurics, magnetotellurics, and audio-magnetotellurics. Microearthquake activity has been shown to have empirical correlation with the more productive parts of geothermal fields. Temperature gradient and conductive heat-flow measurements are important tools in detailed exploration, but oversimplified interpretation of the data therefrom can result in grievous disappointment.

Gravimetry may be employed in both direct, as well as indirect exploration for geothermal steam, depending upon the specific circumstances. Magnetometry may be useful in identifying very high temperature zones (greater than about 500°C) by virtue of loss of magnetism beyond the Curie Point.

Other techniques which are employed occasionally include ground noise mapping, SP, seismic refraction and reflection, and radioactivity mapping.

Each of the above listed techniques has certain merits and weaknesses. A proper combination of techniques, which must be individually tailored for the given region under investigation, could result in success, as shown by examples from a number of localities. Overly simplistic interpretation or overinterpretation of limited data have resulted in exploration failures, as documented in other cases.

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