Fracture Analysis Using Borehole Televiewer Logs in Þeistareykir Geothermal System, NE Iceland

To characterise fracture networks and understand their impact on fluid flow in geothermal reservoirs, an integrated study of borehole televiewer image logs is performed from six wells in the Þeistareykir geothermal field in the Northern Volcanic Zone of Iceland. The characteristics of natural fractures are identified in terms of their occurrence, orientation and relative distribution. Fractures are more concentrated in the eastern part of the field and there is an observed spatial variability in the fracture trends ranging from NNW-SSW, N-S, NNE-SSW to NE-SW. A relationship between lithology and fracture character is also observed as hyaloclastites exhibit a broad dispersion in fracture orientation and a lower fracture density compared to the deeper basaltic and intrusive rocks. The results of BHTV fracture analysis also correlate with various temperature and subsurface logs acquired during drilling to provide insights into the faults and fracture zones that could potentially be linked to permeability and fluid circulation in the wells.