Geophysical exploration methods at European sites

Most geophysical exploration methods have been developed for the oil and gas industry, and<br>ever more sophisticated tools and refinements in the different approaches are designed to<br>solve specific problems associated with the detection and characterisation of hydrocarbon<br>reservoirs. The exploration of geothermal resources has profited greatly from these<br>developments, however, the methods cannot always by directly transferred from oil and gas<br>to hot water and/or steam. First of all, physical properties of H2O differ from those of<br>hydrocarbons, resulting in differing responses of physical measurement methods. Secondly,<br>geothermal reservoirs can be found in highly varying geological environments, mostly<br>associated with volcanism, where hydrocarbons are usually not present. Thirdly, the<br>economically most interesting geothermal reservoirs are much hotter than any oil or gas<br>reservoir. At the moderate temperatures comparable to those of hydrocarbons many of the<br>advanced exploration methods are simply cost-prohibitive, as the economic potential of a<br>medium-enthalpy geothermal reservoir is much lower than for an oil or gas well. For these<br>reasons, some of the existing geophysical methods have to be adapted to meet the needs of<br>geothermal exploration or different methods have to be developed and applied.