Successful Hydraulic Stimulation Techniques for Electric Power Production in the Upper Rhine Graben, Central Europe

Abstract

The Upper Rhine Graben is the focus of geothermal interest in Western Europe due to high temperatures, hydraulically conductive fault zones and an extensional stress regime with comparably low horizontal stresses. As of the beginning of 2009, two geothermal power plants are in operation in the Upper Rhine Graben, one EGS research pilot plant in Soultz-sous-Forêts (France) and a commercial plant in Landau (Germany). Both projects aim at the heat extraction from crystalline basement and are re-injecting the produced fluid. In both cases, massive hydraulic stimulations in the crystalline rocks were required in order to achieve hydraulic conductivities sufficient for power production. Different stimulation technologies had to be applied according to the pre-existing structures found in the rock mass at depth. All stimulation operations were water based. Flow rates used ranged from 50 l/s up to 190 l/s. Injected volumes were as high as some 30,000 m³. Observed productivity increases were as high as a factor of 20. The characteristics of the hydraulic stimulations in the different settings of Landau and Soultz are compared in this paper, underlining the fact that the stimulation technologies developed for EGS/HDR appear to be a very useful tool also for the improvement of hydrothermal resources.