129 6. Borehole electrical panels:an experiment boreholes M07, M20, and M08, suggesting a higher clay content in the limestone consistent with the cuttings log and OPTV observations. A distinct low-resistivity anomaly is observed between 86 and 89 m, corresponding precisely to the fractured zone identified on the OPTV. In borehole M08, the cuttings log describes Bathonian and Bajocian limestone with occasional clay layers at depths of 67 m and 86 m. The OPTV imagery reveals darker zones at approximately 90 m, 100 m, and below 110 m. However, no karstic features are observed on the OPTV. The ERT profile indicates that the limestone is generally resistive (ρa >150 ohm·m), except below 110 m where resistivity decreases, likely due to increased clay content or porosity. No distinct low-resistivity anomalies are detected, which is consistent with the absence of karstic cavities intersected by this borehole. Summary The apparent resistivities of the limestone formations are generally greater than 150 ohm·m down to a depth of approximately 110 meters. The only exception is observed in panel M04, where apparent resistivities remain lower throughout the entire section. Below 110 meters, the apparent resistivities measured in boreholes M20, M07, M08, and M11 decrease to values below 100 ohm·m. Lithological data obtained from OPTV imaging and cuttings logs allow for correlating the geological nature of the formations encountered in the boreholes with the ranges of apparent resistivities recorded. Apparent resistivities exceeding 150 ohm·m correspond to carbonate formations of the Upper Aalenian, Bajocian, and, to a lesser extent, Bathonian stages. The exception in borehole M04, where lower resistivities are observed in these formations, can be attributed to the more clayey-marly composition of the limestones described in the cuttings logs and evidenced by generally darker intervals on the OPTV images. The low resistivities measured at the base of the panels likely correspond to marly-limestone facies characteristic of the Aalenian. The three main depth intervals identified by the 3D seismic block (35–40 m, 85–87 m, and 110–115 m) were clearly detected by the electrical measurements (Fig. 5). These conductive anomalies are often confirmed by OPTV images. The level located between 85 and 87 m based on seismic data is detected between 85 and 90 m by electrical methods. Comparison of resistivity panels and optical wall imagery confirms that low-resistivity point anomalies correspond to open, waterfilled karst conduits. Additionally, the karstic level identified through acoustic methods (Mari and Porel, 2018; Mari, Porel, and Delay, 2020; see also Chapter 5, Mari 2026) at approximately 100 m depth in borehole M20 is also detected by electrical panels (Fig. 6 and 9). This level exhibits a double conductive anomaly and is particularly well defined on
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