| Title | History of Chemical Composition of Geothermal Fluids, Krafla, Northeast Iceland, with Special Emphasis on the Liquid Phase |
|---|---|
| Authors | Halldór ÁRMANNSSON, Thráinn FRIDRIKSSON, Jón BENJAMÍNSSON, Trausti HAUKSSON |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | Krafla, liquid phase, chloride, sulphate, corrosion |
| Abstract | There are no surface springs in the Krafla area so the first studies on the liquid phase were carried out when the first two exploration wells were drilled in 1974. These revealed a dilute geothermal fluid with sulphate dominating over chloride but with a significant carbonate contribution. Sodium was the major cation and the quartz temperature close to the measured temperature. The area has later been divided into several sub-areas but the production wells that followed were like the exploration wells drilled in the Leirbotnar sub area and showed similar characteristics. Gas from magma entered the system during the Krafla fires 1975-1984, mainly in the Leirbotnar sub-area. Drilling was moved to Suðurhlíðar and Hvíthólar where the effects of the gas did not interfere. The Leirbotnar system has been divided into an upper liquid dominated part at a temperature at c.a. 200°C, and a lower two phase part at c.a. 300°C. The Suðurhlíðar system follows the boiling point curve closely and is two phase to vapour dominated at depth. The Hvíthólar system follows the boiling point curve to about 100 m depth but its lower part is cooler. The Suðurhlíðar fluid is very dilute but in most cases chloride dominates over sulphate or is of a similar concentration. In Hvíthólar the chloride concentration is greater than that of sulphate but the converse is true of the lower part fluid. In 1990 to 2000 a relative increase in sulphate concentration and an accompanying decrease in chloride concentration was observed in several wells often with a decrease in quartz temperature. This was ascribed to a cold inflow into the area. This change appears to have levelled out. During the Krafla fires bursts of corrosive fluids of low pH and high chloride were intermittently observed in some wells. Since 2000 some deeper wells have been drilled, at least two of which have hit magma. In these wells chloride is the main anion and pH is low where a liquid phase has been obtained and the steam has contained HCl , which has formed hydrochloric acid upon contact with liquid water and thus proved corrosive. |