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Preprints
https://doi.org/10.5194/se-2020-48
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2020-48
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 29 Apr 2020

Submitted as: research article | 29 Apr 2020

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A revised version of this preprint is currently under review for the journal SE.

On morphology and amplitude of 2D and 3D thermal anomalies induced by buoyancy-driven flow within and around fault zones

Laurent Guillou-Frottier1,2, Hugo Duwiquet1,2,3, Gaëtan Launay4, Audrey Taillefer5, Vincent Roche6, and Gaétan Link7 Laurent Guillou-Frottier et al.
  • 1BRGM, Georesources Division, 45060, Orléans, France
  • 2ISTO, UMR7327, Université d'Orléans, CNRS, BRGM, 45071 Orléans, France
  • 3TLS-Geothermics, 31200, Toulouse, France
  • 4Laurentian University, P3E2C6, Sudbury, Canada
  • 5CFG Services, 45060, Orléans, France
  • 6ISTEP, UMR7193, Sorbonne Université, CNRS-INSU, 75005, Paris, France
  • 7GET, UMR 5563, Université Toulouse III-Paul Sabatier, CNRS, IRD, CNES, 31400, Toulouse, France

Abstract. In the first kilometres of the subsurface, temperature anomalies due to heat conduction processes rarely exceed 20–30 °C. When fault zones are sufficiently permeable, fluid flow may lead to thermal anomalies much higher, as evidenced by the emergence of thermal springs or by fault-related geothermal reservoirs. Hydrothermal convection triggered by buoyancy effects creates thermal anomalies whose morphology and amplitude are not well known, especially when depth- and time-dependent permeability are considered. Exploitation of shallow thermal anomalies for heat and power production partly depends on the volume and on the temperature of the hydrothermal reservoir. This study presents a non-exhaustive numerical investigation of fluid flow models within and around simplified fault zones, where realistic fluid and rock properties are accounted for, as well as appropriate boundary conditions. 2D simplified models point out relevant physical mechanisms for geological problems, such as thermal inheritance or splitting plumes showing a pulsating behaviour. When permeability is increased, the classic finger-like upwellings evolve towards a bulb-like geometry, resulting in a large volume of hot fluid at shallow depth. In the simplified 3D models, where fault zone dip angle and fault zone thickness are varied, the anomalously hot reservoir exhibits a kilometre-sized hot air balloon morphology, or, when permeability is depth-dependent, a funnel-shape geometry. For thick faults, the number of thermal anomalies increases but not the amplitude. The largest amplitude (up to 80–90 °C) is obtained for vertical fault zones. At the top of a vertical, 100 m wide, fault zone, temperature anomalies greater than 30 °C may extend laterally over more than 1 km from the fault boundary. These preliminary results should motivate further geothermal investigations of more elaborated models where topography and fault intersections would be accounted for.

Laurent Guillou-Frottier et al.

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Laurent Guillou-Frottier et al.

Laurent Guillou-Frottier et al.

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Latest update: 11 Jul 2020
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Short summary
In the first kilometres of the subsurface, temperature anomalies due to heat conduction rarely exceed 20–30 °C. However, when deep hot fluids in the shallow crust can flow upwards, for example through permeable fault zones, hydrothermal convection can form high-temperature geothermal reservoirs. Numerical modeling of hydrothermal convection shows that vertical fault zones may host funnel-shape, km-sized, geothermal reservoirs whose exploitation would not need to drill at depths below 2–3 km.
In the first kilometres of the subsurface, temperature anomalies due to heat conduction rarely...
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