Geothermal gradient and geology of Hoffell low-temperature field, SE-Iceland

Abstract

The study area is a part of the Geitafell central volcano in southeast Iceland. This area has been studied extensively for the exploration of geothermal resources, in particular low-temperature, as well as for research purposes. A geological map is the foundation on which a geothermal exploration is based. All other data need to be interpreted in view of the observed or known geological features. During geothermal exploration, geothermal maps should emphasize on young igneous rocks that could act as heat sources at depth. They also show the distribution and nature of fractures and faults, and the distribution and type of hydrothermal alteration. This report describes the results of a geothermal and geological mapping project in a lowtemperature geothermal field in SE-Iceland. The aim of the study was to familiarize the author with geothermal gradient mapping, interpretation of geological information, including tectonic structures and low-temperature geothermal manifestations, as well as to study the site selection for production/exploration well drilling. Another goal of this study was to make geological and geothermal maps of a volcanic field and to analyse whether some relationship could be established between the tectonic setting and the geothermal alteration of the study area. The geothermal model of the drilled area is consistent with the existence of a structurally controlled low-temperature geothermal reservoir at various depths ranging from 50 to 600 m. Televiewer data showed that Wells ASK-29, ASK-50, ASK-56, ASK-82, and ASK-83 drilled in the area have open fractures and show a comparatively high geothermal gradient, indicating that further drilling for exploration/production should be executed. A geothermal map is presented on which possible drilling targets for a production well are suggested.