Abstract
The geothermal powerplant of Soultz-sous-Forêts (France) is investigating the possibility of producing more energy with the same infrastructure by reinjecting the geothermal fluid at lower temperatures. Indeed, during the operation of the powerplant, the geothermal fluid is currently reinjected at 60–70 °C in a deep fractured granite reservoir, and the MEET project aims to test its reinjection at 40 °C. A 3D hydrothermal study was performed in order to evaluate the spreading of the thermal front during colder reinjection and its impact on the production temperature. In the first step, a 3D structural model at fault scale was created, integrating pre-existing models from 2D vintage seismic profiles, vertical seismic profiles, seismic cloud structure and borehole image logs calibrated with well data. This geometrical model was then adapted to be able to run hydrothermal simulation. In the third step, a 3D hydrothermal model was built based on the structural model. After calibration, the effect of colder reinjection on the production temperature was calculated. The results show that a decrease of 10 °C in the injection temperature leads to a drop in the production temperature of 2 °C after 2 years, reaching 3 °C after 25 years of operation. Lastly, the accuracy of the structural model on which the simulations are based is discussed and an update of the structural model is proposed in order to better reproduce the observations.
Highlights
The Upper Rhine Graben is known for its great potential for the exploitation of geothermal energy at high temperatures
The initial goal was to use the heat in the deep crystalline rocks to produce electricity by fracturing the granite to create an artificial heat exchanger as part of a hot dry rock (HDR) project
The first 3D structural model of Soultz-sous-Forêts was built in 1994 [10] from well data and seismic profiles interpreted by the BRGM [11]
Summary
The Upper Rhine Graben is known for its great potential for the exploitation of geothermal energy at high temperatures. An initial phase of drilling, stimulation, circulation tests and observation was carried out until 2007 to study the crystalline rock and the feasibility of future operations This showed that hydrothermal fluid circulation was occurring in the natural fracture system. In existing EGS plants, it plans to demonstrate the feasibility of reinjecting at lower temperatures, down to 40 ◦C, increasing the potential heat valorization of 30% For this purpose, various investigations have been carried out in the framework of the MEET project, regarding the on-site feasibility of colder reinjection [7] and its chemical effects [8]. The objective of the works presented here was to evaluate the potential consequences of a decrease in the injection temperature on the production temperature on a long-term basis
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