In conventional geothermal-electricity generation, wells are drilled deep into fractured, high-temperature rock. Naturally occuring hot, pressurized water and steam are allowed to flow through the wells to the surface to turn steam turbines and produce electricity. Naturally occuring geothermal reservoirs are, however, limited in size, extent and duration. One mechanism of extending the resource is through the design and construction of Enhanced Geothermal Systems (EGS).

With EGS, an incipient reservoir is targeted within a volume of rock that is hot, tectonically stressed and fractured. However, due to secondary-mineralization processes, those fractures have sealed over time, resulting in low permeability. Through a combination of hydraulic, thermal, and chemical processes, the target EGS reservoir can be 'stimulated', causing the fractures to open, extend and interconnect. This results in the creation of a conductive fracture network and a reservoir that is indistinguishable from conventional geothermal reservoirs. This process could serve to extend the margins of existing geothermal systems or to create entirely new ones wherever appropriate thermal and tectonic conditions exist. The figures to the right serve to illustrate this process.