Exploitation of the continental intercalaire aquifer at the Kebili geothermal field, Tunisia

Abstract

The "Continental Intercalaire" aquifer is an extensive horizontal sandstone reservoir and ranks as one of the largest aquifers in the world covering 600,000 km2 in Tunisia, Algeria and Libya. In the Kebili area in southern Tunisia, the geothermal water is about 25-50 thousand years old and of the sulphate-chloride type. The depth of the reservoir ranges from 1,500 to 2,800 m. The piezometric level is about 20 bars and the flow trend is directed from the south and southeast to the north and northwest. During 18 years of exploitation the production rate has reached an average of 4 Mm3/year and several problems have emerged, the most important being severe corrosion of wellheads, scaling in pipelines and pressure decline in the reservoir. The VARFLOW program was used to simulate production and predict the drawdown until year 2020. The predicted drawdown is about 38 to 60 m, assuming an increase in production by 400 l/s. More detailed water level monitoring and closer cooperation between all producers is recommended. This study concludes that the wellheads are not being corroded from within by the geothermal fluid, but from the outside by a brine that develops due to unfavourable wellhead design and atmospheric conditions.