Geochemical Monitoring of the Reykjanes Geothermal Reservoir 2003 to 2013

Abstract

This paper presents data collected for chemical monitoring of the Reykjanes production from before the commissioning of the 100 MWe Reykjanes Geothermal Power Plant in 2006 to present. This includes the concentrations of dissolved minerals and gases and stable isotope composition of the deep liquid, as well as CO2, H2S and CH4 emissions from the production wells. The most notable chemical changes in the Reykjanes reservoir fluid is that several wells, in particular the directional wells producing from the reservoir south of the SW part of the production field have exhibited gradual increase in the concentrations of the most abundant dissolved solids (Cl, Na, K, and Ca) since the commissioning of the power plant in 2006, most likely indicating progressive boiling in the reservoir. Other wells do not exhibit this trend. Lately the concentrations of dissolved solids in the deep geothermal solutions has levelled off to some degree and even showed some decrease. The concentrations of CO2 and H2S in the deep liquid remain more or less constant with time. The concentrations of N2 and Ar have decreased gradually since 2006. This is clear from the CO2/N2 and H2S/N2 ratios in the deep liquid which decreased gradually in 2006–2010 but has since levelled off, perhaps indicating that the influence of progressive boiling is becoming less significant.