The Soultz-sous-Forêts geothermal site : an example of Enhanced Geothermal System
Scientific researchers and engineers are working on Soultz-sous-Forêts geothermal site, located in the north of Alsace (50km north of Strasbourg), to move forward research and knowledge on deep geothermal energy and improve exploitation techniques for this natural heat source.
The Soultz-sous-Forêts project is, nowadays, the world most advanced research program on EGS geothermal energy.
An exceptional underground : a vast natural deep geothermal reservoir.
Two main features for a remarkable site are gathered in the underground of Soultz-sous-Forêts area :
- A heat source : the geothermal gradient is noticeably higher than normal (3 times more between surface and 1km deep), known since the oil exploitation in the area at the beginning of the 20th century.
- An abundant natural fluid allowing heat transport towards the surface : a natural brine (with a salinity 3 times higher than sea water) moves in the granite natural fractures and circulates upon great distances (several kilometers). Thus, the temperature is homogenized between 1000 and 3500m deep and the geothermal gradient is reduced (10°C/km instead of 100°C/km).
Four deep wells : a developed access to the reservoir
Four deep wells allow to reach the fractured granite at a depth of 5000m. Their large diameter permits a maximal circulation of the geothermal fluid. The diameter of the well is 50cm at the surface and decreases with depth to reach 8,5 inches at the bottom of the well. All the wells are cased to 4500m deep, which make them mechanically steady, watertight. That prevents contacts between the natural fluid of the deep reservoir and the underground close to the surface. The horizontal connection between the wells and the reservoir is limited to the last 600m of the well.
The well heads are located on two sites :
- GPK1 platform, where the first GPK1 well was drilled (to 3600m deep) and where the management site office is located (GEIE Heat Mining), is situated along the departmental road D28 (between Soultz-sous-Forêts and Kutzenhausen).
- GPK2 platform, where the well heads GPK2, GPK3 and GPK4 (to 5100m) are gathered and where the power plant is located, is situated along the departmental road D264 (between Soultz-sous-Forêts and Surbourg).
In the reservoir, a hot brine (between 140 and 200°C) circulates naturally.
Natural fluid circulation enhancement : stimulations
In the geothermal loop, the fluid circulation can be enhanced at two levels thanks to stimulation :
- Improvement of the connection between the well and the reservoir : it is necessary to develop the connectivity between the well and the reservoir as the diameter of the well is small compared to the size of the reservoir.
- Improvement of the circulation in the fractured reservoir : The geothermal loop includes a circulation between the wells in the reservoir, a second step consists on developing the connectivity between the wells within the reservoir, at large-scale.
In both case, the aim is to stimulate existing fractures thanks to hydraulic, thermal, or chemical techniques : increase hydraulic conductivity and improve the geothermal fluid flow.
This is the core of EGS technology.
21 janvier 2015