| Title | Comparison of Down-Hole and Surface Resistivity Data from the Hellisheidi Geothermal Field, SW-Iceland |
|---|---|
| Authors | Svanbjörg Helga Haraldsdóttir, Hjalti Franzson, Knútur Árnason, Gunnlaugur M. Einarsson and Hédinn Björnsson |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | Resisitivity logs, 3D resistivity, MT, TEM, high temperature geothremal field, Hellisheidi, Iceland, Petrel |
| Abstract | Resistivity-logs from boreholes are compared to a previously interpreted resistivity model from TEM and MT electromagnetic soundings in the high temperature geothermal field at Hellisheidi, which is a part of the Hengill volcano system, SW-Iceland. Previous studies of resistivity from the geothermal system in the Hengill area have shown a low resistivity cap on the outer margins of the reservoir underlain by higher resistivity and further down a deep conductor which is below the depth of the present study. The resistivity pattern was explained with conduction of temperature alteration minerals which remained when a geothermal system cooled, thus the resistivity could be regarded as a “maximum thermometer”. A low resistivity layer is also present in the well-logs in this study. On the other hand the depth and extensions of the low resistivity zones do not coincide completely with the interpreted resistivity from the surface measurements. Farther down there are less similarities between the results where relatively thin low resistivity layers appear in the resistivity logs. At depth there is less resolution in the interpreted resistivity from TEM and MT and no such small patterns appear. Examples of recent results of XRD-analysis of hydrothermal alteration clay minerals are shown with the well logs. Simplified geological profiles and hydrothermal alteration minerals were compared to the resistivity logs with promising results. A remaining question yet to be confirmed is if borehole logging can be further interpreted with respect to present or previous temperature, even as early as at the end of drilling. |