| Abstract |
Structures such as fractures and faults play an important role as fluid flow pathways in geothermal reservoirs located in active tectonic regions. Fracture networks can act as either conduits or barriers to the movement of fluids and regulate the permeability, heat flow and associated geothermal activity in the subsurface. The Þeistareykir geothermal system in the Northern Volcanic Zone (NVZ) of Iceland is known to be structurally controlled. Geothermal drilling results reveal substantial variations in temperature and permeability across the field, with relatively cooler temperatures observed in wells drilled outside of the main fault and fissure system. Fracture analysis based on borehole televiewer interpretation highlights the structural character of the permeable feed zones, and zones with similar characteristics but no active fluid circulation in wells. These observations strongly indicate that geothermal fluid movement in Þeistareykir is constrained by the fault and fracture networks, but a detailed understanding of the actual structural controls is lacking. Many questions remain concerning the distribution of heat and fluid flow in the geothermal system. Therefore, a range of geological, geophysical, petrophysical, and drilling data from the Þeistareykir geothermal field are incorporated into building a 3D model to better understand the mechanisms of these structures and how they control the subsurface fluid flow processes in this structurally complex environment. A thorough characterisation of the structural network is key for predicting reservoir behaviour, defining geothermal reservoir boundaries and ensuring the sustainable management and long-term utilisation of geothermal resources. |