| Keywords |
Eskifjordur, geothermal field, low temperature, district heating, lumped parameter modeling, pressure response, reinjection, production predictions, cooling predictions, tracer test |
| Abstract |
The geothermal system in Eskifjordur has been utilized since 2005, mainly for space-heating. There are two production wells in the geothermal field, ES-1 and ES-2A, currently producing around 77 °C hot water. In addition to these production wells there are three relatively shallow reinjection wells, FB-32, FB-35 and FB-37, of which well FB-37 has been most actively used. This paper is based on a compilation of production, reinjection, and water table data from wells ES-1, ES-2A, and FB-37 that span the period from 2013 to 2017. The data is used to calibrate a lumped parameter pressure response model to predict the water table in well ES-2A as a function of time and net production from the geothermal system. With this model we make forward predictions for four different scenarios: current production, with and without reinjection, and fifty percent increase in production, with and without reinjection. According to the predictions the geothermal system in Eskifjordur should be able to sustain current production and a fifty percent increased production, at least until 2040, assuming that reinjection is continuously maintained. Moreover, we present the results of a tracer test carried out in the area. Temperature of the production fluid in wells ES-1 and ES-2A has been steadily declining since reinjection started in 2009; going from 82°C down below 78°C in 2017. To estimate future drop in production fluid temperature a tracer test was performed in March 2017. Three different tracer chemicals (2-naphthalene sulfonate, 2,6-naphthalene disulfonate, and 2,7-naphthalene disulfonate) were injected into wells FB-32, FB-35, and FB-37. The concentration of the tracers was then measured in samples collected regularly from production wells ES-1 and ES-2A. Based on the result of the tracer test a 1D analytical flow model was calibrated. Along with the data from the tracer test, temperature data from the period of reinjection was also used in the calibration via a temperature model based on the flow model. The temperature model was used to make future predictions of water temperature in wells ES-1 and ES-2A for different scenarios of reinjection into wells FB-32, FB-35, and FB-37. We find that with the current reinjection scheme the water temperature will have dropped to 74°C in well ES-1 and 73°C in well ES-2A by 2040. But the temperature model predicts that this temperature drop can be mitigated by distributing the reinjection between wells FB-35 and well FB-37, with a 30/70 combination giving the best results. |