| Title | The Application Of THC Code TOUGHREACT-Pitzer On Failure Conditions Of Geothermal Project GeneSys |
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| Authors | Fabian Nitschke, Sebastian Held, Thomas Himmelsbach, Thomas Kohl |
| Year | 2015 |
| Conference | European Geothermal Workshop |
| Keywords | |
| Abstract | The genesys project aimed to demonstrate the feasibility of utilizing geothermal energy from deep‐seated tight sediments to supply the buildings of the bgr in hanover with heating energy. The idea was to establish a coaxial single borehole system, where the geothermal fluid is produced from the inner string and injected via the annulus of the same well. Therefore in 2009 groß‐buchholz gt1 was drilled down to 3901 m yielding a downhole temperature of 170 °c. To supply the heat demand of the buildings 2 mw of geothermal heat extraction were planned. For the development of a reservoir in the virtually impermeable sediments of the middle buntsandstein in may 2011 a frac was created by injecting 20 000 m3 of fresh water. The created frac is assumed to extend over a fracture area of 1 km2 (Tischner et al. 2013). After about 6 month of shut in period a circulation test was carried out. Fluid was produced during three major cycles from the buntsandstein reservoir and was then reinjected without heat extraction into the permeable more shallow wealden sandstone in 1175 m of depth. Immediately after exchanging the production string volume, the brine salinity strongly increased up to an oversaturated state with respect to halite for the achieved production temperatures (Hesshaus et al. 2013). Halite started to precipitate in the surface installation as well as in the wellbore. As a result injectivity into the wealden formation has strongly decreased during the 3rd cycle, whereupon production was stopped. The annulus was flushed with freshwater in order to dissolve the precipitations. Thereafter it was not possible to resume production. In the production string a massive salt plug has been formed between 655 m and 1350 m depth (Hesshaus et al. 2013). This plug completely clogged the well. Production was no longer possible and operations had to be stopped until further notice. This study focuses on the numerical modelling of the conditions within the well leading to the salt plug. The goal is to build up a coupled chemical reactive transport model of the well groß‐buchholz gt1. |