REASSESSMENT OF THE THELAM÷RK LOW TEMPERATURE GEOTHERMAL SYSTEM IN N-ICELAND FOLLOWING SUCCESSFUL DEEPENING OF WELL L?N-10

Abstract

The Thelamˆrk low-temperature geothermal system in N-Iceland has for the last nine years been a source of hot water for the Akureyri District Heating Service. The main production well in the Thelamˆrk field, L?N-11, was drilled in 1992 intersecting a productive fracture at 450 m depth yielding 17 l/s of 91?C water. Geochemical data indicated deep reservoir temperatures around 100?C and drilling experience in the region shows that the best feed-zones are usually at depths between 1000 to 1500 m. Instead of drilling a new well to hit this target an old 900 m deep well, L?N-10, was deepened and deviated towards the main fracture-zone of the system. The well intersected a good feed-zone at 1700 m depth with a temperature about 103?C. A five-month production test was performed with careful monitoring of production rates, water level changes and water temperature for well L?N-10 as well as five other wells in the field. Observed water level changes were simulated with lumped parameter models. The simulation results indicate that the Thelamˆrk reservoir has a volume of about 1 km3 and an average permeability of 1 Dm. Predicted water level changes during long-term production indicate that the geothermal system will sustain a production between 20 and 21 l/s of 103?C water for the next 8 years, with a draw-down less than 245 m. The deepening of well L?N-10 has resulted in an increase in the energy production potential of the Thelamˆrk geothermal system from 4.4 MWt to 6.4 MWt.