Interpretative approach of electrical resistivity data for efficiency implantation of drilling on basement zone : Case of Guibéroua (Côte d’Ivoire)

Access to drinking water for all is a major challenge for all countries, especially developing ones. In Côte d'Ivoire, many efforts are still being made to sastify the water needs of the population. This is the case in Guibéroua where geophysical campaigns have been carried out beforehand in order to increase the success rate of drilling. At the end of a geophysical campaign, sites (F1, F2 and/or F3) are identified in order of priority in each locality. However, these sites, as well as the proposed preferred drilling order, may not be the best ones. The problem then arises of identifying relevant geophysical criteria in order to increase the chances of success at the first drilling attempt. This work proposes an approach to interpreting electrical drag data in order to make a judicious choice of drilling sites. From the electrical resistivity data, electrical profiles are constructed. On these profiles, different anomaly shapes are identified and fracturing indices (FI) are calculated. The results obtained show that the anomaly shapes commonly encountered are the "U", "V", "W" shapes; those of "M" shape are rare. The highest average fracture index (IFm) is observed in the "V" shaped anomalies. This indicates that these correspond to the most fractured zones and therefore the most likely to be water-bearing. Moreover, the boreholes that have been drilled there have provided good flows for village hydraulics. U-shaped anomalies have a low mFI. They therefore describe less fractured sites. This is confirmed by the very low flow rates of the boreholes that have been installed there. As for the "W" anomalies, although the mFI is low, they are ideal for drilling because of the high flow rates obtained.

This study shows that in addition to the shape of the anomaly, the fracture index is an important parameter that must be taken into account when choosing drilling sites. The use of these two parameters can guarantee a high success rate of drillings.

KEYWORDS : Electrical resistivity, Electrical profiles, Conductive anomaly, Fracturing index, Drilling.