The Geothermal Borehole Of Thonex, Canton Of Geneva - Stratigraphic, Tectonic, Diagenetic, Geophysical And Hydrogeological Aspects

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Journal Article: The Geothermal Borehole Of Thonex, Canton Of Geneva - Stratigraphic, Tectonic, Diagenetic, Geophysical And Hydrogeological Aspects

Abstract
The present paper addresses the major results and findings of a geothermal exploration well, drilled directionally at a depth of 2530 m (2690 m drilled length) at Thonex (Geneva) by the Geneva Canton Department of Energy (OCEN) with the financial support of the Swiss Federal Department of Energy (OFEN). The drilling first intersected the Tertiary Molassic coves, then the Cretaceous formations followed by the target Upper Jurassic limestones and finally ended in marry limestones of Jurassic age. Ground water was hit in the Upper Jurassic reef limestones, but at rates below expectations as a result of poor reservoir performance and low well productivity. For this reason, the drilling and completion of a reinjection-well had to be cancelled. Well testing via air lift indicated a stabilized flowrate of 11 m(3)/h, originating from Upper Jurassic limestones at a depth of about 1900 m and a fluid temperature of 70 degrees C as evidenced by production logging. Although no uncontaminated water sample representative of the Upper Jurassic aquifer could be sampled, hydrochemical monitoring suggests a rather weakly mineralised formation fluid (1 to 2g/l TDS) of either the NaCl or NaHCO3 type. The geothermal gradient, measured at 3.12 degrees C/100 m, is close to normal values. Vitrinite reflectance measurements show a normal increase indicative of a paleogradient in the 3.0 to 3.5 degrees C/100 m range.

Authors 
J. Jenny, J. P. Burri, R. Muralt, A. Pugin, R. Schegg, P. Ungemach, F. D. Vuataz and R. Wernli








Published Journal 
Eclogae Geologicae Helvetiae, 1995





DOI 
Not Provided
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Citation

J. Jenny,J. P. Burri,R. Muralt,A. Pugin,R. Schegg,P. Ungemach,F. D. Vuataz,R. Wernli. 1995. The Geothermal Borehole Of Thonex, Canton Of Geneva - Stratigraphic, Tectonic, Diagenetic, Geophysical And Hydrogeological Aspects. Eclogae Geologicae Helvetiae. (!) .