Numerical modeling of reinjection and tracer transport in a shallow aquifer, Nesjavellir Geothermal System, Iceland

Esteban Gómez-Díaz*, Samuel Scott, Thomas Ratouis, Juliet Newson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


Reinjection of excess water from the power production process in the Nesjavellir geothermal field has increased the temperature of shallow groundwaters, posing a risk to cold water wells used for the power plant as well as the ecosystem in Lake Thingvellir. Here, we present a numerical model of fluid flow and heat transport in the shallow reinjection zone to elucidate the flow path of reinjected liquid and the impact of reinjection on the temperature of groundwaters. The permeability structure of the model is based on a 3D geological model of the area. The numerical simulation is calibrated against underground water temperature data measured between 1998 and 2018 and data from a tracer test performed in 2018–2019. The model reproduces the overall temperature field and shows how a high-permeability lava flow together with rift-parallel normal faults act as permeable channels controlling fluid transport. If injection continues, the temperature along the lava flow increases considerably and spreads vertically to much deeper levels, generating a narrow warm zone along the main fault. If shallow injection ceases, temperature drops rapidly at the surface, but decreases slowly around the reinjection zone over 20 years. The numerical model in this study allowed a better characterization of the fracture–matrix interface and the porosity of post-glacial lava flows, contributing to sustainable management of the geothermal resource and the surrounding environment.

Original languageEnglish
Article number7
JournalGeothermal Energy
Issue number1
Publication statusPublished - Dec 2022

Bibliographical note

Funding Information:
The authors thank Reykjavik Energy (OR) for providing valuable data, assistance, and support during this research. Due to the nature of this research, and the data policy of the entity that owns the dataset, the supporting data are not available for sharing publicly.

Publisher Copyright:
© 2022, The Author(s).

Other keywords

  • Dual porosity
  • Fluid flow
  • Geothermal reinjection
  • Heat transfer
  • MINC
  • Numerical modeling
  • Tracer injection


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