Chemical composition of the discharge fluid from IDDP-2, Reykjanes, Iceland

Abstract. Well IDDP-2 was drilled through deepening of RN-15 which is one of the geothermal wells producing from the Reykjanes field (Iceland). It was drilled in 2016 and 2017 as part of the Iceland Deep Drilling Project (IDDP), which aim has been to assess the economic viability of supercritical fluids utilization. Well testing, temperature and pressure logging of RN-15/IDDP-2 together with sampling of the discharge fluid was carried out in 2022 to investigate the well production properties and its feeding aquifers. The chemical composition of the discharge samples obtained during the recent RN-15/IDDP-2 flow test in 2022 suggests a slightly higher reservoir temperature of 294 °C compared to 290 °C in 2016. Most of the major non-volatiles are in a low range of the concentrations calculated for the Reykjanes deep reservoir. The RN-15/IDDP-2 feeding aquifer is, however, enriched in gases such as CO2, H2S, N2, and H2 compared to their content before drilling. In general, the temperature, gas content and the discharge composition suggest that part of the fluid entering the well originates at greater depths compared to the depths of the main feed zones in other Reykjanes wells. Additional research is required to evaluate if the discharge of the well has a signature of a fluid that originates at depths corresponding to supercritical conditions of seawater (T > 403 °C, P > 285 bar).