Sampling and analyses of geothermal steam and geothermometer applications in Krafla, Theistareykir, Reykjanes and Svartsengi, Iceland

Abstract

Krafla, Theistareykir, Reykjanes and Svartsengi are high-temperature geothermal areas in Iceland. In this report the results of sampling and analyses of fumaroles in Krafla, Theistareykir, and wells and fumaroles in Reykjanes and Svartsengi are presented. The results of the chemical gas analyses of samples from fumaroles and wells in these fields were used to estimate the temperature of reservoirs using selected gas geothermometers. Gas geothermometer temperatures were also calculated for wells in Reykjanes and Svartsengi. The estimated reservoir temperature for the Krafla sample is 315°C. The gas geothermometers predicted temperatures ranging between 227 and 406°C with a median value of about 290°C. The estimated reservoir temperature for Theistareykir is 280°C. The gas geothermometers predicted temperatures ranging between 220 and 395°C with a median value of about 310°C. The estimated reservoir temperature for the Reykjanes fumarole samples is 295°C. The gas geothermometers predicted temperatures ranging between 240 and 430°C with a median value of about 280°C. Geothermometer results for wells in Svartsengi (SV-11, 14, 19) range between 122 and 430°C whereas the measured well temperature is 240°C. The median of the geothermometer results for the Svartsengi wells ranges from 229°C for well 19 to 289°C for well 14. The measured temperature in well 12 at Reykjanes is about 290°C but the range of temperatures obtained from gas geothermometers is 192-447°C with a median value of 256°C. The best fit between predicted and observed/estimated temperatures was obtained by different gas geothermometers for individual samples, but Giggenbach´s CH4/CO2 geothermometer consistently predicted temperatures that are 100-200°C above estimated reservoir temperatures.