Fractures System Characterization for the Low-Temperature Laugaland Geothermal Field

Abstract

The Laugaland geothermal field is located on the southern flank of the South Iceland Seismic Zone, a tectonically active strike-slip area connecting the East and West Volcanic regions of Iceland. The field is operated by Veitur Utilities and provides hot water for the district heating systems in Hella, Hvolsvöllur and the neighbouring rural area. Shortly after production started from the field, reservoir pressure declined dramatically with limited production. This occurred in spite the feed zones encountered in the production wells being high-yielding. Ever since the district heating system started operation, its operators have been struggling with declining reservoir pressure and rising demand. Traditional methods for locating more resources in the area have proven unsuccessful, time and time again. Drilling is by far the highest capital cost for developing these resources further. After two failed drilling attempts, it was time to step back and start again with a detailed tectonic study of the area. This field has proven to be successful for extracting and injecting water from feed zones with a favourable local and regional stress (NS and NE fractures) from which the best wells have been located closer to before. This, summed to the previous conceptualization where a high influence from fractures is present, are the main motivation for this work, where previous lineament mappings were analysed, filtered and re-traced as possible surface faults to be then classified and correlated with subsurface observations from borehole televiewer logs' interpretations, allowing to start generating intensity-based correlations according to fault-related fracturing mechanisms. Additionally, fractures' geometrical parameters such as orientation and dimensions along with their distribution through depth have been quick-looked, all of which could be further added to the current well planning strategies.