The Falkenberg Geothermal Frac-Project: Concepts and Experimental Results

Abstract

Similar to the Cornwall and the French Geothermal Frac-Projects the purpose of the Falkenberg HDR project was to set up a field laboratory to study hydraulic fracture propagation in crystalline rock at shallow depth and to investigate fluid circulation and heat exchange within such an artificial fracture. The test site selected is situated within the Falkenberg granite massif, NE Bavaria, FRG. Since 1978 6 boreholes were drilled each to a depth of 300 m on a surface area of about 104 m2. While 3 of the holes served for site survey and seismic observations, an about 20 m diameter hydraulic fracture was introduced from a central borehole. Fracture propagation was carefully monitored by passive seismic investigations. This allowed to intersect the fracture by 2 other boreholes and to circulate water through the system. The vertical fracture is exactly aligned with the regional stress field as determined from hydraulic fracturing stress measurement at the eastern boundary of the Southwest German block. During the experiments the fracture width, flow resistance, fluid losses and the effective heat exchange area were determined.