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Hot Dry Rock Technology

Hot dry rock (HDR)-heated geological formation, without water. It is virtually limitless and is more accessible than hydrothermal resources.

One cubic kilometre of hot granite at 250 degrees centigrade has the stored energy equivalent of 40 million barrels of oil. HDR has the worldwide potential to reduce our dependence on fossil fuels.

The Concept originated in USA about 30 years ago. Now different names for the same concept are used depending on geological settings: HDR (Hot Dry Rock), HWR (Hot Wet Rock), HFR (Hot Fractured Rock), EGS (Enhanced Geothermal Systems), DHM (Deep Heat Mining).

The main HDR resource potential in the UK is in the areas with granite batholiths in southwest and northern England where temperatures are predicted to be 200°C at about 5.4 and 6 km.

In the UK the HDR potential was investigated by the Camborne School of Mines at their test site in Cornwall where three boreholes have been drilled to depths of between 2 and 2.5 km. Reservoir characteristics were monitored using logging, microseismics & other geothermal techniques.

Technological problems: difficulty of creating a reliable & a long term reservoir. After 3 years of circulation a thermal short circuit occurred, which resulted in the reduction of water temperature. This is explained by assuming channel flow instead of water flow over a wide heat exchange area.

Due to technological difficulties in commercial utilisation the program was closed in 1993.

The findings have contributed to the Integrated European - HDR Programme at Soultz in Alsace.

There was relatively slow progress due to high costs of drilling, scientific & engineering tests. However currently HDR technology is in transition from research to commercialisation.

The Concept

Heat is generated by special high heat producing granites located 3km or more below the Earth's surface. The heat inside these granites is trapped by overlying rocks which act as an insulating blanket. The heat is extracted from these granites by circulating water through them in an engineered, artificial reservoir or underground heat exchanger.

How it works

Water is injected into a borehole (depth of about 6km) which is heated to about 200°C by surrounding rock. The water is then returned to the surface through another borehole which produces steam to generate electricity or as a source of heat. The water is then re-injected into the first borehole to be reheated and used again.

Advantages

HDR geothermal energy is has the capacity to carry large base loads 24 hours per day.

HDR geothermal energy has lower environmental impact. As the energy is derived from converting heat extracted from hot rocks there are no gas emissions. The process does not produce any waste dumps and has a low noise impact after construction stage. Site disturbance is limited to drill holes and pipelines, and a building to house the power plant.

Disadvantages

Exponential drilling costs with depth

Disposal of soil, water loss

Toxicity/corrosiveness of geothermal “brine”

Noise when drilling

Once the heat is extracted it would take several thousand years for the rocks to be heated again, but it is still generally considered to be a renewable energy source.

Hot Dry Rock Technology
Hot dry rock (HDR)-heated geological formation, without water. It is virtually limitless and is more accessible than hydrothermal resources. One cubic kilometre of hot granite at 250 degrees centigrade has the stored energy equivalent of 40 million barrels of oil. HDR has the worldwide potential to reduce our dependence on fossil fuels. The Concept originated in USA about 30 years ago. Now different names for the same concept are used depending on geological settings: HDR (Hot Dry Rock), HWR (Hot Wet Rock), HFR (Hot Fractured Rock), EGS (Enhanced Geothermal Systems), DHM (Deep Heat Mining). The main HDR resource potential in the UK is in the areas with granite batholiths in southwest and northern England where temperatures are predicted to be 200°C at about 5.4 and 6 km. In the UK the HDR potential was investigated by the Camborne School of Mines at their test site in Cornwall where three boreholes have been drilled to depths of between 2 and 2.5 km. Reservoir characteristics were monitored using logging, microseismics & other geothermal techniques. Technological problems: difficulty of creating a reliable & a long term reservoir. After 3 years of circulation a thermal short circuit occurred, which resulted in the reduction of water temperature. This is explained by assuming channel flow instead of water flow over a wide heat exchange area. Due to technological difficulties in commercial utilisation the program was closed in 1993. The findings have contributed to the Integrated European - HDR Programme at Soultz in Alsace. There was relatively slow progress due to high costs of drilling, scientific & engineering tests. However currently HDR technology is in transition from research to commercialisation.
The Concept Heat is generated by special high heat producing granites located 3km or more below the Earth's surface. The heat inside these granites is trapped by overlying rocks which act as an insulating blanket. The heat is extracted from these granites by circulating water through them in an engineered, artificial reservoir or underground heat exchanger. How it works Water is injected into a borehole (depth of about 6km) which is heated to about 200°C by surrounding rock. The water is then returned to the surface through another borehole which produces steam to generate electricity or as a source of heat. The water is then re-injected into the first borehole to be reheated and used again.
Advantages HDR geothermal energy is has the capacity to carry large base loads 24 hours per day. HDR geothermal energy has lower environmental impact. As the energy is derived from converting heat extracted from hot rocks there are no gas emissions. The process does not produce any waste dumps and has a low noise impact after construction stage. Site disturbance is limited to drill holes and pipelines, and a building to house the power plant. Disadvantages Exponential drilling costs with depth Disposal of soil, water loss Toxicity/corrosiveness of geothermal “brine” Noise when drilling Once the heat is extracted it would take several thousand years for the rocks to be heated again, but it is still generally considered to be a renewable energy source.