| Title | Reinjection and Induced Seismicity in Geothermal Fields in Iceland |
|---|---|
| Authors | Ólafur G. FLÓVENZ, Kristján ÁGÚSTSSON, Egill Árni GUÐNASON and Sigríður KRISTJÁNSDÓTTIR |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | Injection, induced seismicity, geothermal systems, Iceland |
| Abstract | Reinjection data from field operators and seismic catalogue data from the SIL network of the Iceland Meteorological Office (IMO) are used to describe and analyse re-injection into Icelandic geothermal fields and the corresponding seismicity. Unfortunately the resolution of the production and injection data is generally poor and local seismic networks were missing most of the time of exploitation and injection but is now being improved. Fluid has been injected at 11 sites in 9 production fields; 4 low temperature fields and 5 high temperature fields. All the high temperature fields and one of the low temperature fields are located at plate boundaries where background seismicity is high and occur in swarms. Injection and exploitation at all these places seem to induce or modulate the seismicity. Most of these events are below local magnitude 2. No seismicity has been observed where fluid is injected at the 3 sites outside the plate boundaries. Minor injection related seismicity has been observed at the Reykjanes field but high natural seismic swarms occur in the periphery of the production field with maximum observed local magnitude of 4.7. At the Svartsengi geothermal field the induced seismicity is low with largest observed event of 3.2. At the injection sites for the Hellisheidi power plant only minor seismicity has been observed at Gráuhnjúkar while at the Húsmúli injection site huge induced seismicity has been observed with numerous triggered events with magnitude in the range 3 -4. At Nesjavellir we observe moderate seismicity with a few events above local magnitude 2, the largest being 3.2. These events are within the production field but they are not necessarily related to injection rather than the production. At Krafla considerable seismicity started when injection was initiated but the events are generally below magnitude 2.0. At the low temperature field Laugaland í Holtum in the south Iceland Seismic zone lowering of the fluid pressure due to geothermal production and seasonal variation in the pressure seem to modulate the natural seismicity and might have delayed an impending 6.4 event on June 17th 2000 by several years but also affected its exact timing. |