Nesjavellir Geothermal Field

Iceland

Nesjavellir Geothermal Field is located in the Northern part of the Hengill central volcano in South West Iceland. Industrial operations at this site commenced in 1990, with an initial phase of development of 100 MW thermal power plant, which expanded to a current capacity of 120 MWe and 300 MWth, through a total of 30 production wells.

Annual emission of geothermal gases from the Nesjavellir power plant reach up to ~8000 tonnes of H2S and ~15000 tonnes of CO2. Re-injection of geothermal gases into basaltic formations for sequestering the dissolved gases in minerals in the bedrock has proven to be a successful and environment friendly solution to reduce gas emissions at the nearby Hellisheidi power plant.  

The same methodology is planned to be implemented in the Nesjavellir field by 2022, starting with a pilot injection of ~1000 tonnes CO2 per year into the injection well, NJ-18, which is 2136 m deep with temperatures up to 250°C. The planned injection of geothermal gases and fluids into the Nesjavellir reservoir requires the development of a thorough understanding of the structural permeability controlling fluid flow at the injection site. The permeability at the reservoir depth is mainly fracture-dominated though, which is particularly relevant for:

  1. identifying and characterizing the feed-zones and flow-paths in relation to the injection well to be able to monitor the success of the mineralization of the injected gases within the bedrock,
  2. minimize the impacts of re-injection in terms of induced seismicity,
  3. and provide an input to improve the current/implement future numerical reservoir models.

S4CE will support a combination of field and experimental methods in order to characterize the structural permeability at the Nesjavellir geothermal field. Through this combined approach, permeability and the variables controlling it (e.g. effective pressure, presence of macro-fractures and fractures intersections) can be quantified in the laboratory and then further up-scaled through field observations and drone imagery analysis. Analysis of available seismic data and further seismic instrumentation at the Nesjavellir site is also proposed to constrain the 3D geometry of the activated fault zones in the area and the time-dependence of their seismicity with injection, specifically around injection well NJ-18.