| Title | From Exploration to Utilization, Hoffell Low Geothermal Field, Southeastern Iceland |
|---|---|
| Authors | Sigurður G. KRISTINSSON, Heimir INGIMARSSON, Gunnar ÞORGILSSON, Sigurveig ÃRNADÓTTIR, Magnús ÓLAFSSON, Pétur Einir ÞÓRÃARSON, Þórhallur HALLDÓRSSON |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | exploration, Hoffell, wells, televiewer, production, reservoir |
| Abstract | A good progress has been achieved in recent years in drilling of exploration/production wells in Hoffell/Miðfell in Hornafjörður, SE-Iceland. Low-temperature geothermal exploration began in the county of Austur-Skaftafellssýsla at the initiative of the municipalities in 1992. A noticeable heat anomaly was observed in Hoffell with a geothermal gradient of 186°C/km. Chemical analysis indicated that the temperature in the geothermal system might reach 70-80°C. Exploration in Hoffell was under the supervision of Jarðfræðistofan Stapi until 2012 when Iceland State Electricity (RARIK) got the geothermal utilization right in the area. Thereafter, Iceland GeoSurvey (ÃSOR) started the exploration of the area. Lithological measurements were conducted in selected boreholes as well as acoustic televiewer logging. Interpretation of these logs changed the previous ideas, which experts had, about the geothermal system and results showed that it was more complicated than initially considered. Five deep explorations/production wells have been drilled in Hoffell from 2012 and several gradient wells, the outcome of this drilling and the processing of imaging with acoustic televiewer among other lithological measurements in these wells have strengthen the hypothesis that the main convection of water is in northeasterly striking fractures and that the geothermal system is much larger than previously anticipated. Information derived from acoustic televiewer images have been crucial in locating production wells with greater accuracy and thus increasing the likelihood that the wells will intercept open fractures at the right depth. Today four of the five deep wells are productive: HF-1, HF-3, HF-4, and HF-5. Well HF-2 did not prove to be usable as a production well. But it did turn out to be an excellent monitoring well for the system. A lumped reservoir model for the water table of well HF-2 was calibrated using production data from wells HF-1, HF-3, and HF-4. Predictions for the future water table of well HF-2 was made from and including the year 2018. Two production scenarios were considered, 35 L/s and 45 L/s, and each production scenario included predictions with and without reinjection. Predictions for the water tables of wells HF-3 and HF-4 was extrapolated from the water table of well HF-2. The main result is that the system can withstand 35 L/s and 45 L/s production for 20 years. It is though recommended that reinjection starts within 10 years of production to minimize drawdown in the system. |