Geochemical And Isotopic Characterization Of Geothermal Waters Circulation In Carbonatic Gothermal Reservoirs The Greater Geneva Basin (Ggb)
This study focuses on the interpretation of geochemical data collected at cold and hot springs, and at two deep geothermal exploration wells located on the edges and within the GGB (Canton of Geneva, Switzerland). The sampling sites have been selected across two North-South trending sections following the main groundwater flow from the recharge zone to the deep geothermal reservoirs in the Mesozoic carbonatic units. These formations have been drilled by two geothermal exploration wells; the 745 m deep GEO-01 well, where water with a temperature of 34˚C and an artesian flow rate of 50l/s is encountered, and at the 2530 m deep Thonex-01 well, which produces app. 0.1 l/s at a reservoir temperature of 80˚C. Major ions, trace elements, stable isotopes of Oxygen and Hydrogen, Tritium, Sulphur and Carbon isotopes as well as noble gas samples have been collected and analysed. The analyses aim at characterising the fluid circulation in terms of recharge zone, origin of the water, mean residence times, reservoir temperature, and water-rock interactions. The interpretations show that the geothermal waters have a meteoric origin with the main recharge zone being located in the Jura Mountains towards the North. The infiltration is dominated by secondary porosity controlled by intense fracture conditions. Infiltrating water circulates in the Mesozoic Units and the groundwater flow direction is controlled by the geometry of these formations, which gently dip towards south with a 3˚ average dip. Fracture zones associated to sub-vertical strike- slip faults represent the main corridors where waters as well as hydrocarbons and dissolved gas rise towards the surface. Moreover, the highly porous and permeable karstified horizons at the Lower Cretaceous level and the reef complex in the Upper Jurassic represent very promising potential geothermal reservoirs across the whole Geneva Canton for heat production with temperatures ranging from about 30˚C to more than 110˚C.
AAPG Datapages/Search and Discovery Article #90346 ©2019 AAPG European Region, 3rd Hydrocarbon Geothermal Cross Over Technology Workshop, Geneva, Switzerland, April 9-10, 2019