MAPPING OF APPARENT RESISTIVITY VALUES USING THE GEOSTATISTICAL METHOD IN THE GAGNOA REGION

The study aims to identify areas suitable for the installation of productive hydrogeological wells in the Gagnoa region (Ivory Coast). The objective is to improve the drinking water supply in the crystalline basement. The research is based on the geophysical method of electrical resistivity (electrical towing) using a Schlumberger quadripole arrangement. The authors applied a geostatistical approach to a sample of 42 resistivity data points obtained from 51 transects. This approach included a variographic analysis (fitted to a theoretical exponential model) to define the spatial structure, followed by kriging interpolation to map the entire area. Statistical analysis reveals high heterogeneity in the structures, with resistivity values ranging from 63 to 980 Ω·m (average of 411.48 Ω·m). The variogram indicates a practical range of 20.4 km, demonstrating good large-scale interconnectivity of the fractures. The interpolation map reveals that 32% of the region (in the northeast and west) exhibits low resistivities (180–240 Ω·m) associated with conductive shale formations, while the central and northern parts show average values (240–420 Ω·m). The geostatistical approach using kriging proves effective in predicting the distribution of apparent resistivity. Areas with low to moderate resistivities are the most promising locations for future drilling, as they coincide with high fracture densities, which are essential for groundwater flow and storage.