Significance of basin asymmetry and regional groundwater flow conditions in preliminary geothermal potential assessment – Implications on extensional geothermal plays

Extensional domain type geothermal plays, as fertile targets for future resource development, consist of an orogen and an adjoining sedimentary basin of asymmetric physiographic and geologic setting. Preliminary geothermal potential, i.e. prospective geothermal regions, basin-scale flow patterns, heat transfer processes, temperature distribution and appearance of thermal springs were analyzed systematically by numerical simulations in groundwater basins with special emphasis on the effects of basin asymmetry. The importance of basin-scale regional groundwater flow studies in preliminary geothermal potential assessment was demonstrated for synthetic and real-life cases. A simulated series of simplified real systems revealed the effects of anisotropy, asymmetry of the topographical driving force for groundwater flow, basin heterogeneity and basal heat flow on heat accumulation, locations of thermal spring discharge and prevailing mechanisms of heat transfer. As a new aspect in basin-scale groundwater and geothermal studies, basin asymmetry was introduced which has a critical role in discharge and accumulation patterns, thus controlling the location of basin parts bearing the highest geothermal potential. During the reconnaissance phase of geothermal exploration, these conceptual, generalized and simplified groundwater flow and heat transport models can support the identification of prospective areas and planning of shallow and deep geothermal energy utilization, also with respect to reinjection possibilities. Finally, the scope of “geothermal hydrogeology” is defined in a scientific manner for the first time.