The hunt for supercritical water heats up
Breakthrough technologies developed by the EU-funded project DESCRAMBLE could allow Europe to exploit geothermal energy more efficiently and in more locations than is currently possible. The aim is to increase use of this renewable, clean energy source and reduce Europe's dependence on imported fossil fuels.
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By the end of the project in May 2018, DESCRAMBLE’s researchers plan to test the experimental technologies at a geothermal well in the Larderello area of Italy’s Tuscany region.
The well was previously drilled to a depth of 2.2 km. DESCRAMBLE will attempt to extend it to between 3 to 3.5 km below the Earth’s surface. The team aims to show that geothermal plants can operate with water extracted at pressure and heat levels never achieved before.
Previous attempts to reach such depths at other geothermal plants in Italy, Japan and Iceland failed due to the effects of extreme pressure and temperature on fluids, gasses and equipment.
Geothermal energy plants use steam or hot water taken from wells bored up to around 2 km into the Earth’s surface to turn turbines and generate electricity. The wells are usually located in volcanic areas, where hot materials from the Earth’s interior bring heat energy closer to its surface.
However, current drill and extraction technologies limit the depth of the wells, and the amount of energy that can be generated by geothermal plants. The industry would like to go deeper, where pressure reaches more than 218 times air pressure at the surface and temperatures hit 374°C.
At these extremes and above, water reaches what is called a ‘supercritical’ state – a form incorporating aspects of both liquid and steam. In this physical form the water is difficult to handle and very corrosive to current drilling and extraction equipment.
Developing the technologies to drill for and extract this supercritical water is DESCRAMBLE’s main goal. Supercritical water holds up to 10 times more energy than water or steam.
Access to supercritical water would allow geothermal plants to reduce the number of wells needed per unit of electrical production, leading to cost savings and boosting industry’s competitiveness. The ability to drill deeper would also allow other locations to develop their own geothermal plants.
DESCRAMBLE will also develop models that allow companies to predict the behaviour of supercritical water as it is transported to the surface through wells.