Wolfgramm, Marcus and Bloch, Thomas and Bartels, Jörn and Heuberger, Stefan and Kuhn, Peter and Naef, Henry and Voigt, Hans-Dieter and Seibt, Peter and Sonderegger, Michael and Steiger, Torsten and Uhlig, Stephan (2015) Reservoir-geological characterization of a Fractured Limestone: Results obtained from the Geothermal Well St. Gallen GT-1 (Switzerland). In: Proceedings World Geothermal Congress 2015, 19-25 April 2015, Melbourne, Australia.
Full text not available from this repository.Abstract
St.Gallen is situated in the western Molasse Basin (MB), an orogenic foreland basin of the Alps. The aquifer is formed by Upper Jurassic carbonates. In the eastern Molasse Basin (Germany), these carbonates are often dolomitized showing high hydraulic conductivities. For several years, geothermal plants such as Unterhaching have been producing electricity and heat. In 2009, the St.Gallen geothermal project started with a feasibility study based on a small quantity of data. Accordingly, production flow rates of 50 l/s should be possible at temperatures from 145 to 150°C. 3D seismic investigations concretizing the well design in preparation of the geothermal well were carried out. From March to July 2013, the St.Gallen GT-1 well was drilled into the Middle Jurassic down to a depth of 4450 mMD (4255 mTVD). According to plan, the NNE-SSW striking St. Gallen fault-zone could be drilled through in the Upper Jurassic section. The potential Upper Jurassic aquifer was developed from 3992 – 4404 mMD. Yellowish-brown micritic limestones containing residues of siliceous sponges were developed here from 3992 – 4280 mMD, a dark-grey micrite with sponge needles (basinal limestones) from 4280 - 4375 mMD, sandy calcisiltites down to 4404 mMD, and Dogger rocks down to 4450 mMD. In place of the expected Quinter limestones (Helvetian facies), Swabian sponge mass facies were found. Dolomites causing the good permeabilities in the eastern Molasse Basin could be observed very subordinately. Indications of karstification, open porosities and fractures were only scarce. Increased quantities of transparent calcites could be observed only at 4070 mMD and from 4150 – 4210 mMD; white calcites observed from 4315 – 4335 mMD indicate a fault zone with closed fractures. Temperature logs and other parameters show anomalies in three sections indicating inflow zones. The well St.Gallen Gt-1 was acidized several times in July and October 2013 and investigated hydraulically by means of injection and production tests. The produced deep water contains dissolved salts (TDS approx. 25 g/l) and gas. The hydraulic parameters and the structure of the reservoir could be determined by means of the tests. The pressure behavior curves indicated two closed boundaries correlating with faults in the St. Gallen fault zone. The hydraulic conductivity between the two peaks is increased here, but with a limited reach. The inflows are tied strictly to the faults.
| Item Type: | Conference or Workshop Item (Paper) |
|---|---|
| Uncontrolled Keywords: | geosfer ag, Switzerland |
| Subjects: | Methodology > Other-additional study Region > Switzerland > St. Gallen Inducing technology > Geothermal energy production |
| Project: | S4CE > ST GALLEN: geothermal project |