THC-Modelling of Gt1 Borehole Conditions during the 2011 Failed Circulation Test of the Deep Geothermal Project GeneSys in Hanover
2 BGR, Hannover
O 13.7 in Reactive transport modeling
14.04.2016, 16:15-16:30, Audimax A, Geb. 30.95
The project GeneSys had the goal to demonstrate the feasibility of establishing a deep geothermal heat exchanger by only using a single well. It was planned to produce a previously injected fluid from a deep reservoir and reinject it via the annulus of the well into a shallower more permeable formation after heat extraction.
After creating a frac (reservoir) within the Buntsandstein formation in about 3900 m of depth by injecting about 20 000 m3 of fresh water in May 2011, pressure was shut-in. Within 6 month of residential time, fluid dissolved great amounts of solids to TDS values of at least 450 g/kgw. During a production test in November of the same year the production tubing of the geothermal well Groß Buchholz Gt1 was clogged due to the formation of a massive halite plug. Consequently the project was put on hold until further notice.
To understand and quantify the complex coupled thermal, hydraulic and chemical processes, conditions were modelled using the THC code TOUGHREACT. For the evaluation of precipitation and dissolution processes in this highly saline environment, the Pitzer ion interaction model was used for all chemical calculations. As halite solubility is first and foremost thermally driven, temperature measurements during the production test were used to calibrate the model. The thermal behavior of the well was modelled in very good agreement to measurements. Also the location of the modelled salt plug and the total amount of precipitated solids comply to observations on site.
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