| Title | The Response of the Reykjanes Geothermal System to 100 MWe Power Prodution: Fluid Chemistry and Surface Activity |
|---|---|
| Authors | Thrainn Fridriksson, Audur Agla Oladottir, Pall Jonsson, Ester Inga Eyjolfsdottir |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | Reykjanes, Iceland, High-temperature, steam cap, gas chemistry, surface activity |
| Abstract | The 100 MWe Reykjanes Power Plant was commissioned in May 2006. During the first three years of operation the pressure below the boiling level in the production zone has dropped by ~35bar. The drawdown has resulted in a formation of a steam cap in the upper part of the production zone of the system. As a result the discharge enthalpy of deep production wells has increased from 1210 - 1400 kJ/kg (liquid enthalpy at 275 - 310 °C) before May 2006 to 1450 - 1950 kJ/kg in 2008. Two relatively shallow wells (1225 and 960 m) have been drilled to produce saturated steam from the steam cap (enthalpy ~2700 kJ/kg). Unequivocal signs of systematic, long term changes in the chemical composition of the Reykjanes geothermal fluid have not been observed so far. The CO2 concentration of steam from production wells has not increased significantly despite increasing enthalpy of production well discharge. Furthermore, the CO2 concentration in steam from the two dry-steam wells is not significantly higher than in steam from wet wells. The gas concentrations in steam from the steam cap indicate that the liquid feeding steam cap has been significantly degassed with respect to CO2 but not with H2S. The pressure drawdown since May 2006 has invigorated surface activity significantly. The thermal anomaly at the surface has increased in size, particularly toward the south east. Discharge from steam vents in 2007 was almost an order of magnitude higher than in 2004. The soil diffuse degassing of CO2 has increased by 40% and the estimated total steam flow (through steam vents and soil) from the geothermal reservoir has increased by 50% since the power plant was commissioned. The increase in surface activity due to power production appears to be of a comparable magnitude to an increase in activity resulting from earthquakes in 1967. |