| Abstract: | Shallow geothermal prospecting has been undertaken in three zones in Tunisia for which few deep thermal data are available. Five areas have been included in this work, and temperature data from depths between 35 and 335 m from 46 wells in these areas have been analyzed. In addition, thermal measurements have been made on 112 limestones, dolomites, and sandstones to add to the data base.Temperature profiles from the different areas vary substantially from well to well, and these variations depend on both the local and regional geological and hydrological conditions. The shallow thermal gradients vary from 11 mkm-1 to 132 mkm-1, compared with the maximum deep gradient so far observed in Tunisia of 52 mkm-1 (Ben Dhia, 1988). The discrepancies between shallow and deep gradients in the various regions appear to strongly depend on the geological continuity between the shallow and deeper layers, especially in zones where substantial tectonism has occurred.It is concluded that although near surface geothermal data are useful in areas where few deep data are available, great care must be taken in their interpretation, and both regional and local conditions must be considered. Furthermore, predicting the temperature conditions at depth from these observations can be uncertain, and so combining results from such studies with those from deeper data must be done with care.The Zazghouan area appears as an interesting geothermal prospect, while the others need more investigation to be conclusive. |
