The chemical composition of the discharged fluid from IDDP-2, Reykjanes, Iceland

The IDDP-2 well at Reykjanes was drilled by Iceland Drilling Ltd. for HS Orka Ltd. in 2016 and 2017. The well was drilled as part of the Iceland Deep Drilling Project (IDDP), which aim has been to drill deep wells down to 4–5 km depth into geothermal systems in Iceland, involved casing and deepening the production well RN-15 from 2507 m to 4659 m.  Deepening of the well commenced on August 11^th, 2016, and it was completed on January 25^th, 2017. The most recent well test of RN-15/IDDP-2 was on 5^th of May 2022. The well has a casing damage just below 2300 m depth, which hinders any logging below that depth. The main feed zones are probably at the depth of the casing damage (where the main feed zone of RN-15 was located) and at about 3400 m, but there may also be a minor feed zone near the bottom of the well. When the well is opened for discharge, fluid from these feed zones enters the wellbore, flows up the well and eventually reaches a boiling point. The fluid is then two-phase with a gradually increasing steam fraction up to the wellhead. The estimated enthalpy of the discharged fluid is from about 1107 kJ/kg to 1120 kJ/kg and the steam fraction is about 30%. The production from the well was 19.2 kg/s and 22.2 kg/s at wellhead pressure 13.5 bar-g and 7.8 bar-g, respectively. The estimated productivity index is 1.4 (kg/s)/bar, which indicates low-permeability feed zones.

The geothermometry of the collected fluid sample suggests a slightly higher reservoir temperature of 294°C compared to 290°C in 2016. Note that this difference is within analytical uncertainty for SiO₂ analysis. The highest gas content measured during this study was 1.83 wt% and is higher than most of the RN wells. The deep fluid feeding the well is more diluted comparing to the fluid from RN-15 pre-2016. Most of the major non-volatiles are in a low range of the concentrations calculated for the Reykjanes reservoir. The RN-15/IDDP-2 aquifer is, however, enriched in volatiles such as CO₂, H₂S, N₂, and H₂ compared to their content during monitoring or RN-15 in 2004-2016. In general, the temperature and the composition suggest that fluid entering the well is not only sourced from 2300 m aquifer but also from deeper feed zones. 

The IDDP-2 was funded by HS Orka, LV, OR and OS, in Iceland, together with Equinor (former Statoil). The IDDP-2 also received funding from the EU H2020 (DEEPEGS grant no.690771) for all parts of the operation, and ICDP and US NSF (grant No.05076725) for spot coring and part of the related research