Calcite Scaling in Slightly Saline Geothermal Water at Keldunes, Iceland

Abstract

A geothermal field was verified by drilling at Keldunes NE Iceland in 2006. The temperature of the discharge is 76°C and the geothermal water it is slightly saline, 1-2 ‰, depending on various aquifers in the well. The water is of mixed origin, partly derived from geothermal effluent water from the Krafla high temperature geothermal field further inland and water of more local origin. The salinity of the water is derived from local sediments building up the Jökulsá river delta. Production testing of the well revealed severe calcite scaling, but no steel corrosion. In samples obtained from the well at wellhead pressure of 0.5 bar only slight calcite super-saturation was calculated in the geothermal water. During a flow test of 20 months the salinity of the discharged water changed from 1.3 ‰ to about 2 ‰, even though it was sampled at similar pressure conditions. This may indicate that either the salinity of the water in the aquifers has changed with time or that the salinity of the water relies on relative influence of different aquifers, which again is dependent on pressure. The change in salinity may have affected the scaling rate of the water as the more saline samples also showed higher calculated calcite supersaturation. Tests are now being performed in order to find how to produce the well without scaling in distribution pipes. The first results are promising.