Delineating crustal domains favorable for exploring enhanced geothermal resources based on temperature, petro- and thermophysical properties of rocks: A case study of the Soultz-sous-Forêts geothermal site, France

The study aims to develop a novel approach to delineating the domains in the crust suitable for exploring enhanced geothermal resources. Contrary to existing approaches based on interpolation/extrapolation of the geotherms and assessment of fracturing in the vicinity of drilled exploratory boreholes, it is based on using deep 2-D models of the temperature, petro- and thermophysical properties of rocks determined from magnetotelluric sounding results. Their joint analysis in the framework of the numerical scheme including principal component analysis, self-organizing maps, and K-means clustering is carried out. A cluster cross-section of all considered parameters along the profile intersecting Soultz-sous-Forêts (France) enhanced geothermal system is built, which could be regarded as a temperature, petro- and thermophysical “passport” of the study area to be used for delineating the domains in the crust satisfying different criteria and helping to quantify geothermal resources. It is demonstrated that classification based on temperature and permeability models provides sufficient information to delineate crustal domains favorable for exploring enhanced geothermal resources. In particular, two targets with sufficiently high matrix permeability and temperature are determined. Implementing the developed approach may guide the location and optimal depth of exploration/exploitation boreholes, greatly reducing the total drilling costs and the environmental impact.