DEVELOPMENT OF A WIRELINE HYDROFRAC SYSTEM FOR PERMEABILITY AND STRESS MEASUREMENTS AT DEPTHS DOWN TO 2500 M AND TEMPERATURES UP TO 200 DEGREES C.
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.
THIS CONTRACT BUILDS ON THE CONTRACTOR'S PREVIOUS EXPERIENCE, WHICH HAS INCLUDED THE PRODUCTION OF SEVERAL SELF-CONTAINED LOGGING UNITS NOW IN USE BY SCIENTIFIC TEAMS IN OTHER PARTS OF EUROPE, WITH THE AIM OF EXTENDING THE TOOL TO PERMIT ACQUISITION OF A WIDER VARIETY OF DATA DURING DEEP HDR EXPERIMENTS. THE OPTIONS OF INTEGRATING EITHER THE ACOUSTIC TELEVIEWER (CONTRACT NO.G0082D) OR THE ELECTRICAL FRACTURE LOG (CONTRACT NO.G0053F) INTO THE STRADDLE PACKER CHAMBER WILL ALSO BE INVESTIGATED. THE FIRST PART OF THE WORK WILL CONSIST OF DESIGN STUDIES FOR THE FOLLOWING ELEMENTS:
- A CABLE STRING CAPABLE OF PROVING SUPPORT FOR THE TOOL, HYDRAULIC CONNECTIONS FOR PACKER OPERATION AND FLUID INJECTION, AND ELECTRICAL CONDUCTORS FOR DATA TRANSMISSION;
- A STRADDLE PACKER ASSEMBLY CAPABLE OF WITHSTANDING DIFFERENTIAL PRESSURES UP TO 50 MPA AND TEMPERATURES OF 200 DEGREES C;
- A HIGH-PRESSURE PUMPING SYSTEM (SEVERAL LITRES/SEC AT 70 MPA)
- MISCELLANEOUS SUPPORTING EQUIPMENT.
THE SECOND PART OF THE WORK WILL CONSIST OF CONSTRUCTION OF A PROTOTYPE, WITH THE AIM OF USING THE COMPLETED TOOL IN THE SOULTZ BOREHOLE LATE IN 1987 (SEE ALSO CONTRACT NO.G0072F).