Geophysical exploration of the Helgavatn low-temperature field, W-Iceland and the Árskógsströnd area N-Iceland

Abstract

Helgavatn, W-Iceland, and Árskógsströnd, N-Iceland, are two fracture dominated low-temperature geothermal fields in Iceland. Geophysical exploration there was aimed at locating the upflow zones of the geothermal water. At Helgavatn head-on resistivity profiling was chosen to try to detect permeable near-vertical fractures, which are seen as low-resistivity structures. The results of computer modelling of the three Helgavatn head-on profiles show good correlation with known faults and dykes and indicate that the main hot springs at Helgavatn are located at the intersection between a WNW-ESE trending fault and a NE-SW trending dyke. At Árskógsströnd a study of the general tectonics of the area was carried out, including a.o.t. study of air photos, an analysis of microearthquakes in the area and on-site inspection. Accompanying this was the drilling of 12 shallow gradient wells to locate areas of anomalously high temperature gradient where good fracture permeability might also be expected. Two interesting areas were located, one in Ytri-Vík in the southern part, and the other at well site ARS-6, which is located between the two small villages, Litli-Árskógssandur and Hauganes. Further gradient wells around ARS-6, followed by a deeper exploration well, are recommended in order to find hot water for the villages. Some low-temperature fields in Greece resemble the Icelandic fields dealt with here. The geophysical methods described could be useful in the exploration of these.