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Fig. 8 | Geothermal Energy

Fig. 8

From: How do the geological and geophysical signatures of permeable fractures in granitic basement evolve after long periods of natural circulation? Insights from the Rittershoffen geothermal wells (France)

Fig. 8

Conceptual model of fracture zones and their geophysical and geological signatures linked to hydrothermal alteration grades in the granitic basement of Rittershoffen. Red zones represent the depth extent of permeable fracture zones. a Specific geological and geophysical signatures of a permeable fracture. b Specific geological and geophysical signatures of a plugged fracture with low residual permeability. The geophysical log anomalies are true anomalies that were found in the GRT-2 well as well as the quartz, illite, and chlorite samples. The hydrothermal alteration facies are as follows: HLOW: low hydrothermal alteration grade, HMOD: moderate alteration grade, HHIG: high alteration grade, HEXT: extreme hydrothermal alteration, and VEIN: quartz vein

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