THE GENESYS-PROJECT: EXTRACTION OF GEOTHERMAL HEAT FROM TIGHT SEDIMENTS

Massive waterfrac tests have been performed at great depth in the Northern German Basin in order to investigate the possibility of accessing geothermal energy from tight sedimentary rock formations. The results of these tests and of post-frac hydraulic experiments showed, that a very large tensile fracture was created by injecting about 20,000 m³ of water at flow rates up to 50 l/s. The fracture initiated in a thin sandstone layer clearly propagated upward and downward through the adjacent clay stone layers and reached a total height of at least 150 m. The high storage capacitance of the fracture is indicative of a fracture area up to 5·10 5 m². The fracture retained a high hydraulic conductivity after pressure relief even though no proppants were used to keep the fractures open. Micro-seismicity was very low during the tests and did not allow to monitor fracture propagation. Despite of the large fracture surface area the long term production flow was too low for geothermal application. A cyclic injection-production scheme however showed promising results.