The Continental Intercalaire Aquifer at the Kébili Geothermal Field, Southern Tunisia

Abstract

The C.I. "Continental Intercalaire" aquifer is an extensive horizontal sandstone reservoir (Neocomien: Lower Cretaceous: Purbecko-Wealdien). The CI is one of the largest aquifers in the world covering more than 1 million km2 in Tunisia, Algeria and Libya. This aquifer covers 80,000 km2 in Tunisia. In Kébili field in southern Tunisia, the geothermal water is about 25 to 50 thousand years old and of sulphate chlorite type. The depth of the reservoir ranges from 1000 to 2800 m.

The piÈzomÈtric level is about 200 meters above the wellhead. The flow rate ranges from 70 to 200 l/s with a temperature that exceeds 60?C. Approximately 95% of the geothermal water is used for irrigation of oases after cooling by atmospheric towers. Partly it is used for heating greenhouses. Most problems are encountered during the hot water utilization, such as scaling in the pipes, corrosion of anchor casing and in some parts of wellheads like valves and monitoring points. Another problem is drawdown of the water level due to the the increasing water demands and salinization by intrusion of salt water from Chotts.