Contribution to Groundwater Research in the World’s Largest Hot Desert: Hydrogeophysical Study for the Apprehension of the Jurassic Aquifer in the Tunisian “Sahara”

Abstract

Southern Tunisia belongs to the Sahara desert, one of the driest regions of the world, where groundwater research is crucial to satisfy the water demand. In this region, the Jurassic aquifer appears as a potential resource. Nevertheless, the related information is too limited to develop a suitable plan for exploitation. The present study aimed for a thorough understanding of the Jurassic series using borehole and seismic reflection data. Well logs from 40 petroleum boreholes were analyzed both qualitatively and quantitatively to define precisely the potential water reservoirs and determine their petrophysical characteristics. Comparison of the various recordings revealed the abundance of sandstone and dolomite deposits in the Sebaia Formation (Dogger–Malm) and the evaporitic composition of the Abreghs Formation (Lias). The Sebaia Formation is enriched in clays toward the south as indicated by well logs correlation and computed shale volumes (V_sh reaching 27.8%). The south-east part of Southern Tunisia contains mostly sandy Jurassic reservoirs, exhibiting the highest estimated porosities (22.8–31%). Lithostratigraphic correlations were established to firstly approach the geometry of the Jurassic aquifer. These correlations highlighted that the Jurassic series have variable depth and thickness along the Dahar structure, which thicken and deepen from the Dahar to the west and disappear in the Jeffara. These findings were further refined by the interpretation of 198 seismic profiles, which display several NW–SE-, E–W- and NE–SW-trending normal faults that influenced the Jurassic reservoirs depth, thickness, facies and petrophysical characteristics as well as groundwater circulation. The present study yielded interesting results that may enormously guide the investigation of the Jurassic aquifer in Southern Tunisia. Furthermore, it may be considered as an example for hydrogeophysical applications in the “Sahara” and other arid zones worldwide.