| Title | Enhancing permeability by multiple fractures in the Krafla geothermal reservoir, Iceland |
|---|---|
| Authors | Eggertsson, G H; Lavallée, Y; Kendrick, J; Lamur, A; Markússon, S |
| Year | 2016 |
| Conference | European Geothermal Congress |
| Keywords | Fracture permeability, Storage capacity, Krafla geothermal reservoir |
| Abstract | The presence of fractures in hydrothermal systems influences the storage capacity and efficiency of fluid flow necessary for successful and sustained exploitation for geothermal energy production. The magmatic-hydrothermal system at Krafla Volcano, North-East Iceland, has been exploited by Landsvirkjun National Power since 1977 to generate electricity. Here, to gain insight on the permeability of the reservoir rock, we present results of laboratory experiments conducted to evaluate the effects of multiple fractures on the permeability and porosity of basaltic rocks (with 10-21% initial porosity) collected at Krafla. A hydrostatic cell was used to measure the permeability and pore volume changes of intact rocks as a function of effective pressure (5-100 MPa). The samples were then fractured using Brazilian tensile tests and permeability measurements were repeated under the same range of conditions. Finally, the samples were fractured a second time and the permeability was measured anew. The results show that the generation of the first macro-fracture induced the most significant permeability and porosity changes. The permeability increase due to the presence of a macro-fracture is highest for the densest samples, with a porosity of <15%. The generation of a second fracture imparts little additional effect on permeability across the range of porosities tested. The findings show that the effective pressure is a key control on the efficacy of fluid flow in intact and especially, fractured rocks. |