Heat Flow Modeling of the Laugarnes and Elliðaár Geothermal Fields

Abstract

The Laugarnes and Elliðaár fields are low-temperature geothermal resources that have been harnessed for the district heating of Reykjavík since the 1930s and 1970s, respectively. Stable reservoir pressures in both systems indicate that these have reached quasi-equilibrium with their recharge. In Laugarnes, near-constant discharge temperatures are observed and in the prevailing models of the resource, the formation temperatures are interpreted to be stable, suggesting a steady-state heat flow. This is typically simplified in these models as a fixed pressure and temperature recharge, and the heat sources needed to support this recharge are not well understood. In this study, new conceptual models are proposed where recharge from the surface is extracting the heat from shallow formations as it percolates into the deeper productive zones. To quantitatively test this, a TOUGH2 numerical model was built where numerical simulations successfully replicated the natural state and production history by only using an elevated conductive heat flux as a boundary condition. The results demonstrate how a proposed heat extraction could support the production from the reservoir, suggesting a plausible heat source for the systems.