EGS: What is an Enhanced Geothermal System?
In some cases, very little pressure is needed to cause a permeability increase. In other cases, high pressure may be needed. It depends on the in situ fracture patterns, stress magnitudes/orientations, and rock strength. Once the permeability has been increased, production can be sustained by injecting water (supplemented as necessary from external sources) into injection wells and circulating water through the newly created permeability, where it is heated as it travels to the production wells. As the circulating water cools, the engineered fractures, induced seismicity, and chemical dissolution of minerals may also create new permeability, continually expanding the reservoir and exposing more heat to be mined.