Enhanced Geothermal Systems (EGS) and Unconventional Geothermal Resources (UGR) correspond mainly to blind geothermal resources which are much more difficult to estimate and to explore from surface due to the lack of hydrothermal manifestations like in conventional high enthalpy fields. At the scale of Europe, the strategy for finding EGS and UGR is therefore significantly related to the deep seated litho-tectonic conditions. During the ENGINE project, it was stated that heat, stress and fluid pathways as well as the structural inventory of the subsurface are the key elements that could be considered as priority for research needs as well as for defining new geothermal targets.
Then, different EGS or UGR systems can be defined: stimulation of low permeable reservoirs in hot environment, enlarging the extent of productive geothermal fields by enhancing permeability in the vicinity of naturally permeable rocks, supercritical fields, electricity production from medium-enthalpy geothermal resources by binary plants, combined heat and power generation and cascade use of heat resource…
In the future, the possible contribution of Enhanced geothermal energy to the European Strategic Energy Technology Plan at the horizon 2040 requires an evaluation of the stored geothermal energy, i.e. the thermal potential available of the first tenth kilometres of the European continental crust. From very sparse in-situ measurements of temperature in wells at depth, how can we extrapolate the distribution of heat at a continental scale and calculate temperature at depth maps based on an appropriate geological model? For instance, the contributions of geothermal resources embedded in sedimentary basins and/or in basement rocks have to be evaluated. Moreover, coupling thermal conductivity with other physical and chemical parameters (gravimetry, resistivity, seismology…) represents an ultimate achievement for imaging solid earth by providing a thermal tomography.
GIS approaches combining most suitable geodynamical conditions (heat, stress, fractures) and socio-economic criteria (inhabitants, road, river, energy needs…) have to provide EGS potential maps for selecting the most promising areas for geothermal prospecting.