Enhanced Geothermal System (EGS) is a new type of geothermal power technology that does not require natural convective hydrothermal resources. Until recently, geothermal power systems have exploited only resources where naturally occurring heat, water, and rock permeability are sufficient to allow energy extraction. However, by far the most geothermal energy within reach of conventional techniques is in dry and impermeable rock. EGS technologies enhance and/or create geothermal resources in this hot dry rock (HDR) through 'hydraulic stimulation'.
When natural cracks and pores do not allow economic flow rates, the permeability can be enhanced by pumping high-pressure cold water down an injection well into the rock. The injection increases the fluid pressure in the naturally fractured rock, mobilizing shear events that enhance the system's permeability. This process, termed hydro-shearing, is substantially different from hydraulic tensile fracturing used in the oil and gas industries.
Water travels through fractures in the rock, capturing the rock's heat until forced out of a second borehole as very hot water. The water's heat is converted into electricity using either a steam turbine or a binary power plant system. All of the water, now cooled, is injected back into the ground to heat up again in a closed loop.
EGS technologies, like hydrothermal geothermal, can function as baseload resources that produce power 24 hours a day, like a fossil fuel plant. Unlike hydrothermal, EGS appears to be feasible anywhere in the world, depending on the economic limits of drill depth. Good locations are over deep granite covered by a 3–5 kilometres (1.9–3.1 mi) layer of insulating sediments that slow heat loss. EGS wells are expected to have a useful life of 20 to 30 years before the outflow temperature drops about 10 c (18 f) and the well becomes uneconomic.
EGS systems are currently being developed and tested in France, Australia, Japan, Germany, the U.S. and Switzerland. The largest EGS project in the world is a 25-megawatt demonstration plant currently being developed in Cooper Basin, Australia. Cooper Basin has the potential to generate 5,000–10,000 MW.
Read more about Enhanced Geothermal System: EGS Industry, Induced Seismicity, CO2 EGS, EGS Potential in The United States
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