| Title | Using Distinct Chemical Ratios of Boreholes´ Geothermal Brine to Determine Connectivity Between Faults and Fractures in Þeistareykir Geothermal Field in Northeast Iceland |
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| Authors | Julia Lee Reimer, Teitur Hinrichsen, Anette Mortensen, Helgi A. Alfredsson |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | |
| Abstract | During the months of June through October of 2024, a chemical tracer test was conducted by Landsvirkjun at Þeistareykir Geothermal Field in Northeast Iceland. The tracer test served to investigate the aquifers intersected by borehole ÞG-19, a new production borehole whose drilling had been completed in November of the previous year. ÞG-19 was determined to have two major aquifer intervals: an upper aquifer interval at 1100m - 1500 depth at a temperature of 150 C, and lower aquifer interval at 2200-2800 m depth at 260 C. On May 10th of 2024, Borehole ÞG-19 was shut-in, which caused a crossflow of the upper aquifer in ÞG-19 down into the lower aquifer interval, which in turn flowed into surrounding faults and fractures. Boreholes throughout the Þeistareykir Geothermal Field were then sampled to monitor any changes in their water chemistry that would indicate the presence of the upper aquifer brine from ÞG-19. This water chemistry analysis could provide better insight into the connectivity of faults and fractures within the geothermal reservoir. The tracer test continued into October to monitor any further changes after ÞG-19 was put on discharge on September 25th. A potential fault connection between ÞG-19 and ÞG-04, a producing borehole to the northeast of ÞG-19, was identified at both the boreholes’ lower aquifer intervals. Further verification with more detailed analysis of the sampled brine from these two boreholes is ongoing . |