279 10. Feasibility of monitoring cold fronts of geothermal doublets Figure 10.2 Positioning map showing the location of the six identified zones (green polygons) where injection electrodes could be placed. The blue circles are centered on the injection well GEV4, and the green circles on the production well GEV3. The circles have radii of 2 and 4 km. During a logging control in late October 2021, a foreign object was discovered in the GEV4 injection well. Access to this well was then prohibited due to the increased risk of logging tools becoming stuck. Consequently, the production well GEV3 has been selected by default. Since GEV3 is a production well, access will be more challenging for any future repeat measurements. Furthermore, as the cold front develops in the injection well, it is likely that, even if we gain access to production well in the near future, the cold front signal may be too weak to detect. This will be evaluated during detectability tests, but for this campaign, the decision is to focus on validating the methodology (ability to measure the signal at the bottom of the well and theoretical detectability of the cold front) and to test different source configurations, limiting the campaign to a single injection site. Based on the reconnaissance campaign results, site GEN 2 in the Sénart Forest was selected. Although some surface grounding resistances were high, drilling to a depth of about ten meters should allow for the preparation of electrodes that ensure good current injectivity. Additionally, GEN 2 is the closest site to the well’s shoe (2–3 km away) and offers the most suitable conditions in terms of quiet surroundings and adequate space.
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