Geothermal energy activity is monitored at the surface at the Hengill area. This area can be impacted by natural changes, as well as the production of geothermal energy. There is no definite way of discerning whether the changes occur naturally or from human action. The changes in surface activity at Hverahlíð for instance, started when boreholes were drilled in the area. Therefore, it may be inferred that these changes are due to utilisation of geothermal heat in the area, please see map belove.
Energy production at Nesjavellir and Hellisheidi/Hverahlid
In 2022, energy production at Nesjavellir and Hellisheidi was in accordance with the power plants' operating licence and ON Power's objectives. Maintaining the power plants' production capacity at the Hengill area has been one of the company’s most important tasks in recent years. It has been found that the production density is too high in some of the production fields, the pressure drop is considered to be of concern in Hverahlíð field and the negative effects of re-injection are within the Hellisheidi field, please see appendix.
In June 2022, the Parliament Alþingi passed a parliamentary resolution on the updated classification of power plant options, and the geothermal fields Meitlar, Hverahlíð II and Þverárdalur, which are all fields in the Hengill area, are defined in a utilization category. Even though there are no plans for new power plants at the Hengill area, an extension of the current production area is anticipated, to ensure sufficient supply of hot water in the capital area and full production capacity of hot water and electricity at Hellisheidi and Nesjavellir Geothermal Power Plants for the long term. Some preliminary research on the potential of future production areas have already commenced, to facilitate licences and informed decisions on the future of power generation, and to guarantee responsible utilisation of geothermal resources. The formal process of environmental impact assessment and planning for exploratory drilling in Meitill field will begin in January 2023.
Reykjavik Energy Group places emphasis on as responsible utilisation of resources as possible.
Discharge of geothermal fluids at Nesjavellir and Hellisheidi/Hverahlid
Geothermal fluid is reinjected into the geothermal system at Nesjavellit and Hellisheidi Geothermal Power Plants, to protect surface and groundwater, as the geothermal fluid is warmer than groundwater and has a different chemical composition. The aim is also to increase the pressure in the geothermal reservoir, which in turn boosts responsible utilisation. There is full injection capacity for all separator water from both plants. In cases, where geothermal water is disposed of on the surface, the cause is unplanned interruptions in operation, which means that it is not possible to inject everything.
Various research and development projects have been conducted in recent years to fulfil reinjection requirements at Nesjavellir and Hellisheidi, with considerable success, please see appendix.
At Nesjavellir, in 2022, approximately 78% of the geothermal fluid extracted from the geothermal reservoir was reinjected into the system, thereof approximately 10% into the geothermal reservoir. The development of the reinjection utility at the plant in recent years, has resulted in the discharge of geothermal fluid being at all time low over the past years, please see appendix.
Despite the success of the reinjection system at the Nesjavellir Geothermal Power Plant, energy production is nevertheless accompanied by substantial discharge of heated groundwater at the surface, please see graph belove. Groundwater has been extensively monitored in the past by recording boreholes and hot spring temperatures in real-time, and samples have also been collected since the power plant began its operations in 1990. The results do not show a decrease in groundwater temperatures, despite less discharge. The reasons behind these findings are not quite clear at this stage, however, there are indications that hotter injection water is increasingly returning to the groundwater, even though the amount of geothermal water in surface discharges has decreased. Work continues on the development of deep injection and the next phase is to start injecting into a new injection well in the spring of 2023. It is estimated that the well will receive around 30% of Nesjvallavirkjun Geothermal Power Plants’ geothermal water.
A new injection well will be drilled in 2024, and then it is estimated that deep injection will be at least 60% of the geothermal water from the power plant. The mixing of geothermal water with district heating water in the capital area is scheduled for 2026, and it is expected that this will prevent the mixing of geothermal water with groundwater.
At Hellisheiði, in 2022, approximately 68% of geothermal fluid extracted from the geothermal reservoir (separated water and condensate water) was reinjected. The condensate water (dense, pure steam) not used for reinjection evaporated in the cooling towers or was released in shallow reinjection wells. Some 1.1% of the geothermal fluid went into the overflow of the reinjection utility, due to either procedure or incidents in operations, this discharge was minimal, please see appendix.
Increased supply of geothermal water to the capital area
In the summer of 2022, the entire Capital area received heated groundwater from the geothermal power plants in the Hengill area. This water exchange lasted longer than has been done previously. Research into the integration of the capital region's heating supply system so that it is possible to mix geothermal water and heated groundwater from power plants without the formation of scaling, is promising. The project will completely change the operating system of the heating supply and heat production in the geothermal power plants as the aim is to decrease production from low-temperature geothermal fields during the summertime, in order to further utilise the energy that is produced in power plants. The year 2022 was a considerable challenge in terms of surface dispersion at Nesjavellir due to unexpected failures and problems in maintenance projects at Veitur Utilities and ON Power. Despite this, it was possible to keep surface dispersion within ON Power’s targets.
Impact of discharge of geothermal fluids on the ecosystem in bay Þorsteinsvík
Monitoring the ecosystem in the bay Þorsteinsvík, in the lake Þingvallavatn, began before the Nesjavellir Geothermal Power Plant was built. The results of measurements, made by the Natural History Museum of Kópavogur, show that trace elements from geothermal water, previously considered to have a negative impact on the ecosystem, do not show a statistically significant increase.
Analysis of the status of groundwater at Nesjavellir will continue, in order for ON Power to achieve its objective of reducing the environmental impact of the Nesjavellir Geothermal Power Plant.
Induced seismic activity
The reinjection of geothermal fluid can cause seismic activity, known as induced seismic activity, or triggered earthquakes, especially at the Húsmúli area. Blasting, associated with geological research and drilling in high-temperature fields, may also be the culprit. ON Power follows procedures, that are designed to minimise the risk of triggered earthquakes at and around the Hengill area.
In 2022 Reykjavik Energy Group did meet its objective to safeguard that seismic activity, potentially associated with the reinjection of geothermal fluid, would not cause an inconvenience and damage. Two earthquakes of magnitude 3.2 hit ON Power's reinjection area, despite the fact that no significant changes had been made to the reinjection, please see appendix. Therefore no notifications were sent to the Icelandic Meteorological Office's seismic activity division, or the Department of Civil Protection and Emergency Management of the Icelandic Police, due to changes in the process of reinjection in 2022. However, press release was issued to inform the situation.
Appendices and links
- Production, enthalpy, reinjection and drawdown (PDF)
- Release of geothermal water from the Nesjavellir and Hellisheidi geothermal power plants. Groundwater monitoring (PDF)
- Research and development projects to meet injection demands at Hellisheidi and Nesjavellir (PDF)
- Development of seismic activity at the Hellisheidi Geothermal Power Plant since the autumn of 2011 (PDF)