Thermal regime, groundwater flow and petroleum occurrences in the Cap Bon region, northeastern Tunisia

The Cap Bon region of northeastern Tunisia is part of a young continental margin that presents a thick column of sediments deposited mainly during Cretaceous and Miocene extended tectonic episodes. This sedimentary package is characterised by broad synclines alternating with NE–SW trending anticlines, and is affected by numerous NE–SW, NW–SE and E–W striking faults. Oligo-Miocene sandstones constitute the most important potential reservoir rocks in the region.The distribution of subsurface temperatures in the Cap Bon basin reflects local groundwater circulation patterns and correlates with the location of known oil and gas fields. The results of geothermal studies could therefore prove useful in the search for new hydrocarbon resources in the region. Subsurface temperatures were measured in deep oil exploration and shallow water wells. Local geothermal gradients range from 25 to 35 °C/km, showing higher values in the Korbous and Zennia areas, which correspond to zones of groundwater discharge and convergence in the Oligo-Miocene aquifer system, respectively.Analysis of thermo-hydraulic and geochemical data relative to the thermal springs in the Korbous region along the Mediterranean coast has made a useful contribution to geothermal prospecting for potential deep reservoirs. Positive geothermal gradient anomalies correspond to areas of ascending thermal waters (i.e. discharge areas), whereas negative anomalies indicate areas of infiltrating colder meteoric waters (i.e. recharge areas). The zones of convergence of upward-moving water and groundwater may be associated with petroleum occurrences.