Geowissenschaftliche Bewertungsgrundlagen zur Nutzung hydrogeothermaler Ressourcen in Norddeutschland

In Germany low enthalpy thermal waters (mainly with temperatures between 40 C and 100 C maximum temperatures partly above 100 C) are of great importance in the exploitation of hydrogeothermal energy. Large thermal water reserves, high realizable flow rates (50-100 m"3/h) and high productivity (>50m"3/hxMPa) are the main requirements for efficient economic exploitation. Thus usage is restricted to certain geologic conditions and special reservoir properties. One of the most favorable German areas for direct geothermal heat recovery is the North German Basin. Mainly Cretaceous-, Jurassic- and Triassic sandstone reservoirs in a depth range between 1000 and 3000 m can be utilized there. Detailed geologic and petrophysical investigations of the reservoir rocks, knowledge about their temperature conditions, chemical and microbiological analysis of the formation waters and the estimation of possible fluid-rock interactions are on the hand of the basis for an evaluation of the regional energy potential and on the other hand the main basis for a locally successful technical exploitation. Reliable and efficient geothermal heat supply requires proper management of the thermal water loop of the geothermal plant. This includes economic and energy as well as environmental aspects. The design of the geothermal loop has to be optimized according to the specific conditions of each site. Today reliable technical solutions exist even for the highly concentrated geothermal brines of the very permeable but sensitive sandstone aquifers in North Germany. Initial Fe"2"+ content of the reducing Na-Cl-brines and the possible precipitation of iron hydroxides induced by oxygen entry between production and re-injection well is of main technological importance there. Further investigations within BMBF-project should focus on the secondary use of the thermal waters and on the suitablility of dual-permeability (fissured) reservoirs. (orig./AKF)Geothermie Report 97-1SIGLEAvailable from TIB Hannover: RR 6134(97/15) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman