Reservoir Tracer Test in the Krafla Geothermal Field Using Conservative and Potentially Degrading Liquid-phase Tracers

Abstract

A reservoir tracer test was conducted in the Krafla geothermal field, NE Iceland, in summer 2016 as a part of the EU-FP7 funded project IMAGE (Integrated Methods for Advanced Geothermal Exploration). Three liquid-phase tracer compounds were injected into well K-39; two naphthalene sulphonate molecules (2,6-NDS and 2,7-NDS) which are reported to be thermally stable at temperatures exceeding 300°C but degrade at higher temperatures, and potassium iodide (KI) from which the iodide ion is presumed to be conservative. Tracer recovery was only observed in one out of five monitoring wells; well K-19. The first tracer breakthrough was observed within 26 hours of injection and the recovery peak about 15 days after injection. The fast tracer recovery shows that there is a strong connection between the two wells. One-dimensional convection-diffusion models were fitted to the measured concentration data, resulting in a good fit for all tracer types. The excellent correspondence of the calibrated parameters for all three tracers suggests that no thermal breakdown of two NDS compounds has occurred.