Enhanced geothermal system


An enhanced geothermal system generates geothermal electricity without natural convective hydrothermal resources. Traditionally, geothermal power systems operated only where naturally occurring heat, water, and rock permeability are sufficient to allow energy extraction. However, most geothermal energy within reach of conventional techniques is in dry and impermeable rock. EGS technologies expand the availability of geothermal resources through stimulation methods, such as 'hydraulic stimulation'.

Overview

In many rock formations natural cracks and pores do not allow water to flow at economic rates. Permeability can be enhanced by hydro-shearing, pumping high-pressure water down an injection well into naturally-fractured rock. The injection increases the fluid pressure in the rock, triggering shear events that expand pre-existing cracks and enhance the site's permeability. As long as the injection pressure is maintained, high permeability is not required, nor are hydraulic fracturing proppants required to maintain the fractures in an open state.
Hydro-shearing is different from hydraulic tensile fracturing, used in the oil and gas industry, which can create new fractures in addition to expanding existing fractures.
Water passes through the fractures, absorbing heat until forced to the surface as hot water. The water's heat is converted into electricity using either a steam turbine or a binary power plant system, which cools the water. The water is cycled back into the ground to repeat the process.
EGS plants are baseload resources that produce power at a constant rate. Unlike hydrothermal, EGS is apparently feasible anywhere in the world, depending on the resource depth. Good locations are typically over deep granite covered by a layer of insulating sediments that slow heat loss.
Advanced drilling techniques can penetrate hard crystalline rock to depths of up to, or exceeding, 15 km, providing access to higher-temperature rock as temperature increases with depth.
EGS plants are expected to have an economic lifetime of 20–30 years.
EGS systems are under development in Australia, France, Germany, Japan, Switzerland, and the United States. The world's largest EGS project is a 25-megawatt demonstration plant in Cooper Basin, Australia. Cooper Basin has the potential to generate 5,000–10,000 MW.

Research and development

EGS technologies use a variety of methods to create additional flow paths. EGS projects have combined hydraulic, chemical, thermal, carbon-based, and explosive stimulation methods. Some EGS projects operate at the edges of hydrothermal sites where drilled wells intersect hot, yet impermeable, reservoir rocks. Stimulation methods enhance that permeability. The table below shows EGS projects around the world.
NameCountryState/regionYear StartStimulation methodReferences
MosfellssveitIceland1970Thermal and hydraulic
Fenton HillUSANew Mexico1973Hydraulic and chemical
Bad UrachGermany1977Hydraulic
FalkenbergGermany1977Hydraulic
RosemanowesUK1977Hydraulic and explosive
Le MayetFrance1978Hydraulic,
East MesaUSACalifornia1980Hydraulic
KraflaIceland1980Thermal
BacaUSANew Mexico1981Hydraulic
Geysers UnocalUSACalifornia1981Explosive
BeowaweUSANevada1983Hydraulic
BruchalGermany1983Hydraulic
FjällbackaSweden1984Hydraulic and chemical
Germany1984
HijioriJapan1985Hydraulic
SoultzFrance1986Hydraulic and chemical
AltheimAustria1989Chemical
HachimantaiJapan1989Hydraulic
OgachiJapan1989Hydraulic
SumikawaJapan1989Thermal
TyrnyauzRussia`1991Hydraulic,
BacmanPhilippines1993Chemical
SeltjarnarnesIceland1994Hydraulic
MindanaoPhilippines1995Chemical
BouillanteFrance1996Thermal
LeytePhilippines1996Chemical
Hunter ValleyAustralia1999
Groß SchönebeckGermany2000Hydraulic and chemical
TiwiPhilippines2000Chemical
BerlinEl Salvador2001Chemical
Cooper Basin: HabaneroAustralia2002Hydraulic
Cooper Basin: Jolokia 1Australia2002Hydraulic
CosoUSACalifornia1993, 2005Hydraulic and chemical
HellisheidiIceland1993Thermal
Genesys: HorstbergGermany2003Hydraulic
Germany2003Hydraulic
UnterhachingGermany2004Chemical
SalakIndonesia2004Chemical, thermal, hydraulic and cyclic pressure loading
Olympic DamAustralia2005Hydraulic
ParalanaAustralia2005Hydraulic and chemical
Los AzufresMexico2005Chemical
Switzerland2006Hydraulic
LarderelloItaly1983, 2006Hydraulic and chemical
InsheimGermany2007Hydraulic
Desert PeakUSANevada2008Hydraulic and chemical
Brady Hot SpringsUSANevada2008Hydraulic
Southeast GeysersUSACalifornia2008Hydraulic
Genesys: HannoverGermany2009Hydraulic
St. GallenSwitzerland2009Hydraulic and chemical
New York CanyonUSANevada2009Hydraulic
Northwest GeysersUSACalifornia2009Thermal
NewberryUSAOregon2010Hydraulic
MauerstettenGermany2011Hydraulic and chemical
Soda LakeUSANevada2011Explosive
Raft RiverUSAIdaho1979, 2012Hydraulic and thermal
Blue MountainUSANevada2012Hydraulic
RittershoffenFrance2013Thermal, hydraulic and chemical
KlaipėdaLithuania2015Jetting
OtaniemiFinland2016Hydraulic
South Hungary EGS DemoHungary2016Hydraulic
PohangSouth Korea2016Hydraulic
FORGE UtahUSAUtah2016Hydraulic
ReykjanesIceland2006, 2017Thermal
Roter Kamm Germany2018Hydraulic
United Downs Deep Geothermal Power UK2018Hydraulic
Eden UK2018Hydraulic
QiabuqiaChina2018Thermal and hydraulic
VendenheimFrance2019
Project RedUSANevada2023Hydraulic
Cape StationUSAUtah2023Hydraulic

Australia

The Australian government has provided research funding for the development of Hot Dry Rock technology. Projects include Hunter Valley, Cooper Basin: Habanero, Cooper Basin: Jolokia 1, and Olympic Dam.