TO DETERMINE THE PHYSICAL PROPERTIES OF THE GRANITIC BASEMENT IN THE SOULTZ HDR BOREHOLE.
The results of studies carried out on cores and cutting materials of three boreholes to a depth of 3.6 km are summarised.
The physical property programme included measurements of density, ultrasonic velocities, seismic anisotropy, elasticity, fracture behaviour, electric and magnetic parameters, thermal properties including radioactive heat production, and radioactive age dating.
Heat production in the Soultz granite is 2 to 3 times greater than that in other granites at the surface, although all surface granites in the vicinity show the same intrusion age. The physical property measurement programme has demonstrated that continuous measurements on cores and cuttings are essential for both operational drilling procedures and downhole condition assessment in crystalline rock formations.
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.
THE CORE SAMPLES OBTAINED FROM THE GRANITE SECTION OF THE SOULTZ GPK-1 BOREHOLE WILL BE ANALYSED TO DETERMINE THE PROPERTIES OF THE GRANITE SUCH AS STRENGTH AND FRACTURE TOUGHNESS, THERMAL PARAMETERS, HEAT PRODUCTION (RADIOGENIC CONTENT), AND ACOUSTIC, ELECTRICAL AND MAGNETIC PROPERTIES.
Funding SchemeCSC - Cost-sharing contracts