Geophysical Assessment for Deep Structuring Mapping and Water Resources Perspectivity in semi-arid land region (Northeastern Tunisia, Mediterranean basin)

Abstract

In Mediterranean semi-arid regions, shallow aquifers are generally over-exploited. Several Deeper groundwater boreholes exhibit serious problems of low hydraulic yield and dry wells. The existence of a reliable information about the regional geological structure can enhance the success of deep well programs. Geophysics proved very useful, as a fast and efficient tool to understand the structuring of deep hydrogeology aquifers. Indeed, the identification and characterization of the deep structures of the Bir Drassen – Sidi Toumi region (Cap-Bon, Northeastern Tunisia) contribute to a better quantification of the groundwater potential for asustainable management. This province can be considered as the SW extension of the NE-SW Jebel Abderrahman atlasic anticline, one of the most prominent geological structures in Northeastern Tunisia. To identify the Miocene and Oligocene reservoirs, a geophysical study was carried out, using advanced gravity analysis, supported by boreholes, seismic and geoelectrical calibration. Different gravity filters were applied to reveal the Sub-basins architecture and faulting network in the region. Using the calculation of maxima of Total Horizontal Gravity Derivative and Euler's solutions distribution, a set of deep faults of different directions was divulged. Time Domain Electromagnetic mapping illustrate the influence of fault zones on the regional arrangement of sub-basins aquifers and their recharge processes. Finally, a 3D residual gravity inversion was carried out, to better image the tectonically controlled depocenters associated with prolific thick fluvial-deltaic reservoirs. These “Deep Aquifer Valley” can be suggested as strategic targets for deep hydrogeological exploration planning.