TO CONSTRUCT AND APPLY AN ECONOMIC MODEL FOR HDR SYSTEMS IN THE UPPER RHINE VALLEY, AND TO CO-ORDINATE THE GERMAN HDR EFFORT.
The European Geothermal Project involved teams from France and Germany who collaborated to test a site in the Upper Rhine Valley for its suitability for terrestrial heat mining (hot dry rock (HDR) energy production). Some British scientists participated in specific tasks.
The site was chosen near Soulz-sous-Forets in Alsace at the location of the old oil field of Pechelbronn which was the first oil field field exploited in Europe since the 18th century.
It is situated on 1 of the summits of a very large thermic anomaly (200 km long and 20 km wide) where the mean geothermal gradient between the surface and 1500 m is known to be higher than 6.5 C/100 m. The programme began in July 1987 with a 2000 m deep borehole.
Below at 1375 m thick sediment cover, the granitic basement was penetrated to a depth of 2000 m. The temperature at the bottom of the hole was 140 C. The geothermal gradient within the sediments was unusually high (10 C per 100 m) and diminished to a normal after a series of fractures inside the Bundsandstein producing some water at 116 C with a total salinity 98 g/l. At the depth of 1820 m, hydraulically active natural fissure was reached. The artesian outflow from this zone was 0.15 l/s, with well head pressure of 1.6 bars. The thermal water produced from the well had a high chloride contents and clearly had an identical origin with the fluid collected from the Buntsandstein just above the granite. During the water injection tests, a second active natural fissure was detected normally closed out but which seemed to aquire a noticeable permeability at a well head pressure of about 40 bars.
In a cost benefit model the costs for the construction and operation of an hot dry rock (HDR) plant were considered with respect to the value for the produced electricity (or space heat). The major components of the plant (a doublet of deep boreholes, the stimulated HDR reservoir and the surface installations including pumps for water circulation and the power station) were defined and compiled into a structure diagram which revealed the mutual interactions between the various cost determining factors.
Heat extraction from impermeable hot rock sections in some 1000 m depth implies a complicated and expensive technological system.
The costs for the different components of a HDR system were determined. There was a close interaction between the cost for necessary equipment, the demands regarding temperature and heat production from the geothermal resource during the production period (20 years or more), and the site specific natural conditions, such as geothermal, gradient, natural stress field and other properties. The computer program, HDREC, was developed for the determination of the energy production cost (heat/electricity) under different conditions. Various algorithms describing the performance of the stimulated HDR reservoir were integrated. The program serves for an evaluation of the cost limits, sensitivity analyses (ie cost at different depth) and a definition of research goals for an improvement of the economic performance of HDR systems as well as for the exploration of suitable natural conditions in the underground.
A MICROCOMPUTER MODEL WILL BE DEVELOPED TO EVALUATE THE LIKELY ECONOMICS OF HEAT PRODUCTION FROM POSSIBLE GEOTHERMAL HDR DEVELOPMENTS AT SITES TYPICAL OF THOSE TO BE FOUND IN THE UPPER RHINE VALLEY. THE MODEL WILL TAKE ACCOUNT OF PREVIOUS MODELLING IN OTHER COUNTRIES, NOTABLY USA AND UK, AND WILL ASSIST IN DETERMINING RESEARCH PRIORITIES FOR FIELD DEVELOPMENTS IN THE REGION.
THIS CONTRACT ALSO PROVIDES FOR OVERALL CO-ORDINATION OF THE GERMAN SIDE OF THE FRANCO-GERMAN HDR PROJECT AT SOULTZ (SEE ALSO CONTRACT NOS. G0055D, G0080D, G0081D, G0082D AND G0072F).