287 10. Feasibility of monitoring cold fronts of geothermal doublets Figure 10.8 Amplitude spectrum of the signal emitted by the source (TX), the signal recorded by the surface receiver (RX1), and the signal recorded at the borehole bottom (RX2). Figure 10.9 Simplified geological model for measurement validation. 10.6 Detectability of the cold front To determine if the cold front is detectable, a new modeling is performed. A parallelepiped with dimensions 100×100×100 m (representing a volume of 106 m³) simulating water at 40 °C is inserted at the reservoir level. The resistivity of the cold front is chosen to be 41% higher than that of the reservoir layer (based on the experimental tests), which is at 70 °C. Three measurement configurations are modeled (see Figure 10.10) to evaluate the detectability of the cold front. These configurations represent different scenarios we might encounter. The modeling results are summarized in Figure 10.11. In configuration 1, the magnitude of the secondary field produced by the anomaly (10–⁶ nT) is two orders of magnitude higher than the ambient noise level (10–⁸ nT). This signal-to-noise ratio
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