THM modeling of gravity anomalies related to deep hydrothermal circulation at Soultz-sous-Forêts (France)

• Published in: Geothermal energy (Heidelberg) Vol. 8; no. 1; pp. 1 - 21
• Main Authors: Vallier, Bérénice, Magnenet, Vincent, Schmittbuhl, Jean, Fond, Christophe
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 26-04-2020; Springer Nature B.V; Springer; SpringerOpen
• Subjects: Amplitude; Amplitudes; Anomalies; Circulation; Convection; Convection cells; Deep geothermal reservoir; Earth and Environmental Science; Earth Sciences; EGS; Finite element method; From Exploration to Operation - Research Developments in Deep Geothermal Energy; Geoecology/Natural Processes; Geology; Geophysics; Geotechnical Engineering & Applied Earth Sciences; Graben; Gravimeters; Gravimetry; Gravity anomalies; Gravity meters; Heat flux; Heat transfer; Heterogeneity; Hydrothermal convection; Instruments; Magma; Mathematical models; Profiles; Renewable and Green Energy; Reservoirs; Sciences of the Universe; Spatial variations; Thermal anomaly; Thermo-hydro-mechanical model; Three dimensional models; Two dimensional models; Wavelength; France; EGS; Thermo-hydro-mechanical model; Deep geothermal reservoir; Hydrothermal convection; Thermal anomaly; Thermo-hydromechanical model
• ISSN: 2195-9706; 2195-9706
• DOI: 10.1186/s40517-020-00167-8

Gravity measurements in the Upper Rhine Graben evidence spatial variations at the regional scale and close to the geothermal sites. They are classically interpreted as linked to the geology. We aim to bring new insights on another potential origin of these gravity changes. Our approach is to quantify gravity anomalies related to the deep hydrothermal circulation. A thermo-hydro-mechanical model is developed at the reservoir scale for the Soultz-sous-Forêts site (Soultz), France. A finite element method is used in 2D and 3D. The size of the representative elementary volume is assumed to be 100 m with no regional fault in the reservoir. Surface gravity profiles and maps associated to the large-scale hydrothermal circulation are computed from the variations of the effective density through the model. Synthetic spatial gravity variations in 2D and 3D models are shown to have an amplitude of 0.02 mGal. They are shown to be mostly linked to the convective system. Their wavelength is about 7.5 km, consistent with the width of the hydrothermal convection cells. The anomaly maximum is located at the top of the maximum surface heat flux. However, gravity anomaly observations show much higher amplitude and heterogeneity. Spatial gravity variations linked to the hydrothermal circulation are shown to be smaller than the observed gravity spatial variations, but still measurable with very sensitive instruments (absolute gravimeters).