CIRCULATING THE HDR RESERVOIR AT SOULTZ: MAINTAINING PRODUCTION AND INJECTION FLOW IN COMPLETE BALANCE

Abstract

The geothermal research programme for the extraction of energy from hot fractured rocks at Soultz-sous-Forets started in 1987. The research at
this site is based on what is called the "Soultz concept". This consists first of injecting water at great depth under high pressure in order to establish
efficient connections between a borehole and the natural fracture system in the basement rocks (which at this site already supports some degree of natural circulation) and to improve the transmissivity of this fracture network. Along the direction of the maximum in situ stress, further boreholes are then drilled at the outskirts of the stimulated fracture system. Again massive hydraulic injections are then used to fully connect these boreholes to the previously stimulated fracture network. In the last step the pressure between the boreholes is adjusted in order to force water to migrate between the wells through the "enhanced" natural fracture system. The same techniques may be applicable to future heat extraction from conventional fractured geothermal systems with reduced permeability, a feature which illustrates that the so-called Hot Dry Rock technology is simply part of a continuous spectrum of geothermal activities.