| Title | Stable Gas Isotope Characterisation of the Reykjanes Geothermal Field, Iceland |
|---|---|
| Authors | Finnbogi ÓSKARSSON, Salvatore INGUAGGIATO, Thráinn FRIDRIKSSON, Stefano CALIRO |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | Reykjanes, geothermal field, gas, isotopes, mantle component |
| Abstract | We present gas concentrations and stable isotope results for samples collected from production wells in the Reykjanes geothermal field in SW-Iceland in 2007, 2009 and 2013. The geothermal gas in Reykjanes is characterised by a low 40Ar/36Ar ratio, a N2/36Ar ratio of about 14500 and a negative but variable measured δ15N in N2, suggesting that N2 and Ar are to a large extent surface-derived. The δ13C values measured in CO2 are close to the estimated magmatic 13C endmember for Icelandic geothermal fluids (-3.8‰). The He concentrations and measured 3He/4He ratio have decreased significantly since the initiation of the 100 MWe Reykjanes Power Plant in 2006, especially in the SW-part of the field where production has been most extensive. When corrections have been made for atmospheric contributions to He and N2, the isotopic signature of the deeper component suggests an origin deep in the mantle with R from 15 to 17 Ra and a δ15N down to -17‰. The corrected R and δ15N show a stronger deep mantle fingerprint for the samples collected in 2013 than the older samples. |