Enhanced Geothermal System

Enhanced Geothermal Plant

Enhanced Geothermal Systems (EGS) are a new type of geothermal power technologies that do not require natural convective hydrothermal resources.

Until recently, geothermal power systems have only exploited resources where naturally occurring heat, water and rock permeability is sufficient to allow energy extraction from production wells. However, the vast majority of geothermal energy within reach of conventional techniques is in dry and non-permeable rock. EGS technologies "enhance" and/or create geothermal resources in this hot dry rock (HDR) through hydraulic stimulation.

When natural cracks and pores will not allow for 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 which mobilizes shear events, enhancing the permeability of the fracture system. This process, termed hydro-shearing, used in EGS is substantially different from hydraulic tensile fracturing used in the oil & gas industries.

EGS / HDR technologies, like hydrothermal geothermal, are expected to be baseload resources which produce power 24 hours a day like a fossil plant. Distinct from hydrothermal, HDR / EGS may be feasible anywhere in the world, depending on the economic limits of drill depth. Good locations are over deep granite covered by a thick (3–5 km) layer of insulating sediments which slow heat loss. HDR wells are expected to have a useful life of 20 to 30 years before the outflow temperature drops about 10 degrees Celsius and the well becomes uneconomic. If left for 50 to 300 years the temperature will recover.

Enhanced Geothermal System

There are HDR and EGS systems 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 the Cooper Basin, Australia. The Cooper Basin has the potential to generate 5,000–10,000 MW.