**4.5 Habanero (Australia; after MIT, 2006 and Wyborn, 2011)**

Australia has the hottest granites in the world thanks to radioactive decay characterized by temperatures approaching 250°C at a depth of 4 km in the Innamincka granite (Cooper Basin, south Australia) where the Habanero EGS is developed. Like at Soultz, the Habanero EGS is based on 3 drillings reaching a 4250 m depth. In this white two-mica granite containing 75%SiO2, biotite is widely chloritized, feldspar is also altered and calcite precipitated as secondary mineral as already described for the Soultz granite (see section 3). Some fractures intersected in the first well were overpressured with water at 35 MPa above hydrostatic pressure. The fractures encountered were more permeable than expected likely because of slipping improving their permeability and resulting in drilling fluids being lost into them. The well intersected granite at 3668 m and was completed with a 6-inch open hole. It was stimulated in November and December 2003. A volume of 20000 cubic meters of water was injected into the fractures at flow rates from 13.5 kg/s to 26 kg/s, at pressures up to about 70 MPa. As a result, a volume estimated from acoustic emission data at 0.7 km3 was developed into the granite body. A second well was drilled 500 m from the first one and intersected the fractured reservoir at 4325 m. During drilling pressure changes were recorded in the first well. The second well was tested in 2005 with flows up to 25kg/s and a surface temperature of 210°C was achieved. Testing between the two wells was delayed because of lost equipment in the second well. The first well was stimulated again with 20000 m3 of water and it appeared, thanks to acoustic emission, that the old reservoir was extended by another 50% and finally covered an area of 4 km2. A third well was drilled 568 m from the first one and was stimulated in 2008. The well productivity was doubled. As a result of these stimulations, two parallel fracture planes with a 15°W dip developed separated by about 100 m around 4200-4400 m and 4300- 4600 m depths. The open-loop test performed in 2008 injected 18.5 kg/s in the first well. The third well produced 20 kg/s of water at a temperature around 212°C thanks to flow in the main fracture plane cited before. The productivity obtained during this test was nearly similar to that obtained in the Soultz GPK2 well allowing electricity production from June 2008. The main challenges to future progress are the reduction of drilling costs, an increased rate of penetration for drillings in hard formations, increasing flow rate by improving well connection to reservoir and through development of multiple reservoirs

The Soultz-sous-Forêts' Enhanced Geothermal System:

**6. Conclusion** 

district networks).

**7. References** 

A Granitic Basement Used as a Heat Exchanger to Produce Electricity 499

Enhanced Geothermal Systems experiences at Fenton Hill (USA), Rosemanowes (UK), Hijori (Japan) and Basel (Switzerland) allowed scientists to develop a European thermal pilot-plant producing electricity in Soultz-sous-Forêts (France) since June 2008. This project is the result of 20 years of active research based on geology (petrography, mineralogy, fracture analysis), geochemistry, geophysics (seismic monitoring, well-logging), hydraulics and modelling. Technical improvements were also necessary to allow deep drilling (down to 5000 m) in a hard (granite), highly fractured rock and circulation of water at great depth (between 4500 and 5000 m). The rock behaves as a heat exchanger in which cold water is injected. The water circulates in the re-activated fracture planes where it warms up. It is pumped to the surface and activates a 1.5 MWe geothermal Organic Rankine Cycle power plant that converts the thermal energy into electricity. In such a project challenges are numerous and difficult since the injected water must circulate at great depths between the 3 wells of the triplet with no or little loss and the flow rate and fluid temperature must be and remain high enough to allow production of electricity. Provided careful monitoring of the reservoir during operation, EGS are a sustainable, renewable and clean way to produce electricity. It has been proven that environmental impacts of EGS are lower than those of nuclear or fossil fuel power plants dedicated to the production of electricity. The Soultz EGS pilot plant is the first one in the world to produce electricity and it should be followed in the forthcoming years by industrial units that will produce electricity at a commercial scale. Many other EGS projects have begun all around the world and a lot of scientific and technical targets are in development to improve the production of energy (electricity and central heating through

Baisch, S., Carbon, D., Dannwolf, U., Delacou, B., Devaux, M., Dunand, F., Jung, R., Koller,

Bartier, D., Ledésert, B., Clauer, N., Meunier, A., Liewig, N., Morvan, G, Addad, A. (2008).

Beardsmore, G.R. & Cooper, G.T. (2009). Geothermal Systems Assesment- Identification and

Brown, D.W. (2000). A Hot Dry Rock Geothermal Energy Concept Utilizing Supercritical

*Basel-Stadt, Armt für Umwelt und Energie*, Available at

http://www.wsu.bs.ch/serianex\_teil\_1\_english.pdf

*Mineralogy*, 20 (1), 131-142.

2000, SGP-TR-165.

February 9-11, 2009, SGP-TR-187

M., Matin, C., Sartori, M., Secanelll, R. & Uörös, R. (2009). Deep Heat Mining – Seismic Risk Analysis, *Departement für Wirtschaft, Soziales und Umwelt des Kantons* 

Hydrothermal alteration of the Soultz-sous-Forêts granite (Hot Fractured Rock geothermal exchanger) into a tosudite and illite assemblage, *European Journal of* 

Mitigation of EGS Exploration Risk, *Proceedings of the Thirty-Fourth Workshop on Geothermal Reservoir Engineering,* Stanford University, Stanford, California,

CO2 Instead of Water, *Proceedings of the Twenty-Fifth Workshop on Geothermal Reservoir Engineering*, Stanford University, Stanford, California, January 24–26,

(Wyborn, 2011). The concept of a 25MWe commercial plant is now designed with 3 injection wells and 6 production wells. The ultimate potential is to supply up to 6500 MWe of long-term base-loadpower, equivalent to electrical supply from ~750 MT thermal coal (Wyborn, 2011).
