HYDROGEOPHYSICAL INVESTIGATIONS AND MODELLING OF THE TUNISIAN NORTH AFRICAN PLATE BASINS

Tunisia is a semi-arid to arid country in North Africa. It is facing a water scarcity and quality as the Mediterranean area. Water supply and storage do not respond to the demographic and economic growth and demand. In addition, only 5 10⁹ m³ of water from 35 10⁹ m³ per year renewable water supply are retained and remobilized as surface, dam and groundwater resources. The later are no longer sufficient to the developpment demand. Among the solutions to this problem, geologic, geophysical and hydrogeochemical evaluations and investigations had been undertaken during these last years.

Geophysical and hydro-geochemical approaches had been used as seismic, gravity, electric tomography and geochemical field and laboratory analyses to investigate new deep carbonate and sandstone reservoir aquifers modeling.

Tunisian margin is structured as a mosaic of kilometric Mesozoic Rift Horst platforms and Graben basins, limited by deep-seated E-W, N-S, NE-SW and NW-SE strike slip flower faults.

Seismic reflection sections calibrated to outcrops and hydraulic and petroleum wells as well as hydrogeological well correlations have proven Mesozoic fractured carbonate and multi-layered Cenozoic sandstone reservoirs distributed to unconfined and semi-confined aquifers.

Reservoir petrophysic parameters of fractured carbonate and sandstone porosity range respectively from 8 % to 15 % and from 20% to 40%, a permeability varies from 0,1*10^-4 m/s to 10*10^-4 m/s, a transmissivity from 0,1*10^-3 m²/s to 30*10^-3 m²/s, a salinity from 0 g/l to 5 g/l and the storage coefficient of confined aquifers from 10^-3 to 10^-4.

Hydrogeologic modelling had led to estimate geologic and water reserves as billions of cubic meters and should be a strategic reserves for actual and future in Tunisia.

Keywords: Tunisia, Atlas, Hydro-geophysics, Hydrogeochemics, Reservoirs, Modelling