HYDRAULIC AND MICRO-SEISMIC RESULTSOF A MASSIVE STIMULATION TEST AT 5 KM DEPTHAT THE EUROPEAN HOT-DRY-ROCK TEST SITE SOULTZ, FRANCE

摘要

By 2004/2005 a geothermal pilot plant for electricityproduction shall be completed at the HDR site atSoultz. This plant will consist of two productionwells, one injection well and a reservoir in anambient temperature of roughly 200°C. As a first steptowards this ambitious goal the existing well GPK-2was deepened from 3.8 km, where a large reservoirwas already developed, down to 5 km, where thetemperature requirements for an industrial powerplant have been met. In a second step, a massivehydraulic stimulation with injection rates of up to 50l/s was performed in summer 2000.During this operation a large rock volume wasactivated for seismic slip. The locations of the micro-seismic events show that the mechanically affectedrock volume is rather heterogeneous in shape havingextensions of roughly 2.5 km in length, 0.5 km inwidth and 1.5 km in height. This is the largestvolume ever stimulated in a single operation atSoultz. 3-D analysis and visualization of the seismicdata reveals crucial insights into the internalstructures of the seismic cloud.Hydraulic tests before and after the stimulationconfirmed that the hydraulic properties of the granitewere permanently enhanced. Although the concept ofhydraulic stimulation developed in the shallowersystem of Soultz approved to be also applicable at 5km, some significant differences came out. The stressconditions as well as the connectivity to large scalefractures/faults seem to differ from what wasobserved at shallower depth.