Conceptual and Numerical Models of the Laugarnes Geothermal Field, Reykjavík Iceland

Abstract

The Laugarnes field is a low-temperature geothermal resource used for space heating in Reykjavik since the 1930s. Despite production averaging approximately 160 L/s over the past five decades, reservoir water levels and production temperatures have remained stable. This study examines the factors contributing to this stability in pressure and temperature to improve understanding and prediction of long-term reservoir behavior. A detailed review of historical static temperature surveys reveals "top-down" cooling in the upper few hundred meters of the system, which we interpret as indicative of cold recharge from near-surface formations. In the new conceptual model, this recharge is assumed to extract heat from the formation as it percolates into deeper, more productive sections of the reservoir. Numerical simulations successfully reproduced both the natural state and production history of the field, relying solely on basal conductive heat flux as the heat source and incorporating the effects of shallow recharge. The simulations also captured the temperature decline in the shallow formation and the near-stable discharge temperatures from the wells. These results suggest that shallow recharge and the associated top-down heat extraction mechanism sustain production in Laugarnes and offer an alternative framework for understanding reservoir processes in the field and other low-temperature geothermal systems.