The In-Situ Geothermal Laboratory Gro? Schˆnebeck- Stimulation Experiments of Sandstones in 4200 m Depth

Abstract

Enhanced productivity of thermal water is the indispensable condition for economic and sustainable generation of geothermal electricity. A precondition for this purpose is a sufficiently high temperature above 100 ?C in the reservoir and a production rate of the deep fluids of at least 50 m?/h. The former gas exploration well Gro? Schˆnebeck 3/90, about 50 km northeast of Berlin in the North-German Basin, was re-opened and deepened to a total depth of 4294 m with a 400 m open-hole section of Rotliegend siltstones, sandstones, conglomerates and volcanic rocks. Bottom hole temperature is approx. 150 ?C.

Two intervals of the Rotliegend sandstones were hydraulically stimulated in January 2002. Experiment design comprised isolating the interval by sealing the bottom of the well with sand and the top with a mechanical packer. High viscosity fluid with proppant was employed to stimulate the intervals. Production rates were obtained with a casing lift test and increased to 25 m?/h. To study the steady state conditions a long term hydraulic test was carried out in summer 2002. With a moderate flow rate of 1 m?/h over several weeks a total amount of 700 m? formation fluids were produced. The productivity-index was estimated at steady state conditions to 0,6 m?/h * MPa.

The current productivity is however insufficient for geothermal power production and requires further stimulation experiments. Therefore, stimulation of the volcanic rocks at the bottom of the well are planned in January 2003.