On the way to the exploitation of deep geothermal resources in naturally fractured environments/Vers l’exploitation des ressources géothermiques profondes des systèmes hydrothermaux... - Les numéros thématiques des Comptes rendus - Série Geoscience

In the middle of the 1980s, the so-called Hot Dry Rock (HDR) projects were under consideration, aiming at exploiting the heat stored in deep rocks by circulating heat-bearing fluids in closed loops through fracture networks artificially created in the rock by hydraulic fracturation. The typical geological targets of such projects were hot, and therefore necessarily deep crystalline massifs, which were supposed to be sufficiently tight in order to allow fluid transfers without toomuch loss of heat bearing fluids between the injection well and the production well, through one or several fractures, artificially maintained open under a sufficiently high pressure in order to allow the expected flow. These projects had to face numerous technological questions, and they also promoted an important investment of scientific teams, who realized that: on the one hand, there were very few crystalline massifs, which couldbeconsideredas tightenough in relationwith their low fracturation, for presenting reservoir volumes sufficiently large to allow their geothermal exploitation within the scope of the first generation of HDR concepts; on the other hand, a high number of complex parameters was governing the circulation, in natural systems or in artificially maintained systems, of the fluids present in deep geological systems, which are rich in fractures, more or less open, but which present a very low matrix permeability.