Assessment of scaling and corrosion problems in the Kebili geothermal field, Tunisia

Abstract

Severe scaling problems have been encountered in the pipeline networks in the low-temperature geothermal field in Kebili, South Tunisia, due to the chemical changes resulting from degassing, evaporation and cooling that are necessary to produce a valid water for oasis irrigation. Data from three wells: Kebili-Ras Ela_n-C.I.10, Om Somaa-C.I.5 and Lymagues-C.I.8 was analysed to study the calcium carbonate scaling potential. One scaling sample and two pipe samples from Kebili-Ras Ela_n pipeline network were also analysed for scale identification by microscope and X-Ray Diffraction. The scale consisted mainly of aragonite. Two chemical models, the WATCH program and the SOLVEQ program were used to predict calcite and aragonite scaling, and to determine the allowable supersaturation before calcium carbonate formation becomes a problem. The saturation index, log (Q/K), for the two calcium carbonate polymorphs are high. For calcite the log (Q/K) exceeds 1.50 and for aragonite at the final step log (Q/K) exceeds 1.30, which indicates that the CaCO3 scaling problems will occur. Based on these findings more accurate predictions of calcium carbonate scaling can be made.