| Title | Reinjection Into Two-phase High-enthalpy Liquid Dominated Geothermal Fields in NE-Iceland |
|---|---|
| Authors | Anette K. MORTENSEN, Egill JÚLÃUSSON, Ãsgerður SIGURÃARDÓTTIR, ÃsgrÃmur GUÃMUNDSSON, Bjarni PÃLSSON, Steinn Ãgúst STEINSSON |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Reinjection, Krafla, Theistareykir, Iceland, Geothermal field |
| Abstract | This paper will present an overview of experience gained from reinjection strategies at two high-enthalpy liquid dominated geothermal fields operated in NE-Iceland by Landsvirkjun, the national power company of Iceland. Krafla geothermal power plant has been in operation for more than 40 years, but currently the installed capacity is 60 MWe. Up until 2002 all brine was discharged on the surface, but since 2002 gradually increasing proportions of brine has been reinjected into infield wells deep in the reservoir. Mainly two wells have been used as reinjection wells. Well K-26 is located in the south-western part of the well field and is 300-500 m from the nearest production wells. Reinjection in well K-26 commenced in 2002. Initially the objective with reinjection of 120°C hot brine was to attempt to diminish the corrosive properties of fluids in the lower part of the reservoir, but the main aquifer in well K-26 is at 2050 m depth and is within the superheated part of the reservoir, where temperatures exceed 340°C. In the past 10 years reinjection rates in K-26 have been 70-76 l/s. Signs of thermal or chemical breakthrough have thus far been negligible and have been limited to one well at the edge of the current production field. Well K-39 is located in the southern part of the production field and is 150-300 m from nearby production wells in SuðurhlÃðar. Reinjection in well K-39 commenced in 2013 with the objective to provide pressure support to the reservoir in SuðurhlÃðar, which had experienced decline in production. The main aquifers in K-39 are rather shallow between 1200-1600 m depth. Despite of this reinjection rates have been rather high up to 60 l/s, partially prompted by the objective to reduce surface discharge of brine. Initially a stabilisation in steam output had been observed, however, chemical breakthrough has subsequently been observed as well as enthalpy decrease in nearby production wells, which has prompted a reduction in reinjection in K-39. Work is ongoing to achieve appropriate ratios of reinjection in K-39, which will provide pressure support while at the same time avoiding severe thermal breakthrough. At Theistareykir geothermal field production commenced in December 2017 and the installed capacity has been 90 MWe since April 2018. The initial reinjection strategy at Theistareykir is to reinject all brine into shallow wells above the cap rock of the geothermal reservoir. The reinjection wells are 450 m deep and are located more than 1 km northwest of the main production field, where they have been drilled into the outflow from the geothermal reservoir. Production history is short, but despite of this pressure increase have been observed in monitoring wells west of the production field. |