The productivity from geothermal systems is often controlled by faults and fractures. Faults can have positive effects on fluid flow and heat transport, leading to drilling targets at fault zones. It is, however, under debate which part of the fault might be the most favourable site for drilling. The catalogue of geothermal systems in the Great Basin, Nevada, demonstrates that not the centre of fault planes is the setting for high geothermal activity. Instead, step-over regions, fault intersections and fault tips belong to the favourable structural settings of geothermal fields in the Great Basin. Our attempt aims to explain from a fracture mechanical perspective the cause and effect why faults tips may represent favourable targets for geothermal exploration.
Fault and fracture zones serve as fluid conduit or barrier for fluid flow. The behaviour of faults should therefore be studied and estimated before drilling.
Different concepts exist to qualitatively and numerically characterize fault and fracture zones from hydrogeologic, hydraulic (e.g. Agosta 2007, Bense et al. 2013) structural geological and tectonical (e.g. Johansen & Fossen 2008, Ferrill et al. 2008) or mechanical analysis (e.g. Imber et al. 2008) to explain fluid flow patterns and behaviour of faults in the present day stress field and under reservoir operational conditions.
Fracture mechanics may be another approach to characterize and understand the hydraulic behaviour of fractures. Other than the frequently used empirical failure criteria fracture mechanics is physically based. Fracture mechanics is the study of stress and displacement fields near a crack tip leading to fracture propagation. Fractures in solid materials determine the strength of the material. Inglis (1913) and in particular Griffith (1921), were the first to recognize the importance of pre-existing discontinuities as precursors to failure of solid materials. Today, fracture mechanics is mainly employed to recognize pre-failure rock mass behaviour that may result in predicting or averting the potential for geotechnical and geological failure (Szwedzicki 2003).
