EGS needs water in large quantities. Sea water may be used.
With EGS/DHM, Geothermal energy is now an option even for countries without natural ‘hot fields’.
Most natural geothermal fields occur at the periphery of tectonic plates.
Malta is situated between the Eurasian and African plates, in a zone characterized by pull-apart rifting.
Malta is situated within a general area considered geothermally hot.
Tectonic plate movement
Tectonic plate processes
Malta's tectonics and stratigraphy
Pelagian Area(U.S.G.S. Bulletin 2202D)
Geothermal Gradient Map
Malta platform
The average geothermal gradient (Fig.20) in wells on the Malta platform (about 2°C/100 m) is slightly lower than the basin of Ragusa (2.2°C/100 m) and Sirte (2.6°C/100 m). However, the gradient at well AQ, located near the edge of the platform and closest to the study area, is 2.3°C/100 m (Fig.21). By extrapolation, a temperature of 100°C would be reached at about 3,600 m, marking the onset of significant oil generation.
Source: Bishop W.F.& Debono G., Hydrocarbon Geology of Southern Offshore Malta and Surrounding Regions, Journal of Petroleum Geology Vol 19/2 April 1996 pp 129-160
Geothermal Gradients in Malta Wells
Post-Miocene time has been a period of active tectonics in the Pelagian Block , as indicated by the Sicily channel rift complex with its volcanic islands (Pantelleria and Linosa) and submarine volcanic centres (Calanchi et al., 1989).
Therefore, higher geothermal gradients may be present off the stable Malta platform. A relationship between Cretaceous volcanic rocks and geothermal gradient was assumed in east-central Tunisia by Bishop (1988), and
Fig.21 shows a marked increase in gradient from 1.4°C/100 m to 3.6°C/100 m in Jurassic volcanic interval at depths of about 3,800 m in well MSA. |
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Hottest Regions
Crust Thickness
The predicted crust thickness corresponding to the Malta plate is about 18 – 20 km. The temperature gradient cannot be really linear, as rock formations are heterogeneous, yet it is intuitive that at deep levels, temperatures will rise sharply.
The technology is available to drill in granite to 15 km depths and more. Drilling in sedimentary formations is much easier and at a fraction of the cost.
Sedimentary EGS needs less fracturing stimulation
Granite may hold more heat because of isotope decay, but it is much harder to reach deeply.
Crustal Model
Small Power Plants
Once the wells are drilled and the rigging removed, EGS plants are small and low profile.
Air condensing Hawaii plant
Water cooled condensation could make this installation even less obtrusive.
Highest Contribution Efficiency
‘Contribution efficiency’ is the ratio of energy generated per year to the installed (operating) capacity
Compared to other RES, geothermal energy has the highest contribution efficiency, which is:
- Geothermal = 6.4 GWh/ MWe
- Solid Biomass = 5.5 GWh/ MWe
- Hydroelectric = 3.6 GWh/ MWe
- Wind = 1.9 GWh/ MWe
- Solar PV = 0.074 GWh/ MWe IEA - GIA 2005 Annual Report, p.5
- Although some RES may cost less per MW installed, they operate for a fraction of the time!
EGS in Europe
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Many EU countries with access to Nuclear, Hydro, Wind, Bio and Natural Gas resources are also developing EGS
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Soultz
EGS, while starting slowly in the USA more than 30 years ago, is becoming more important each year.
There are many projects underway, notably the Soultz project in France, which started electricity production in June 2008.
Inauguration of Soultz plant
President Sarkozy |
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CW: Power installation, ORC plant, Geothermal loop, Isobutane filling
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CW: The Site, Salt for brine, Circulation, Well head
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