How can we meet the world’s growing energy demand at the same time as reducing CO2? One promising technology is geothermal energy, which allows us to use the earth’s natural heat as a clean source of energy. Nina Romich and Philipp Strauss tell us how, where and when this works.

“Geothermal energy is the use of heat stored in the earth’s crust,” explains Philipp Strauss, exploration geologist at OMV. “The temperature of the earth increases as you go deeper, by about 3 degrees per 100 meters. As a result, the water at a depth of several thousand meters is over 100 degrees Celsius. And that means lots of environmentally friendly thermal energy available to us.” But how do you get the heat out of the ground and how can you use it?

“Geothermal wells are similar to wells for oil or gas. A geothermal doublet consists of two boreholes, a producer and an injector.”, explains Nina Romich, project developer at OMV in the Low Carbon Business unit. The producer pumps hot reservoir water to the earth’s surface, and the thermal energy is transferred to a second fluid via a heat exchanger. “After the heat is transferred, the reservoir water is pumped back into the earth with the injector to maintain the pressure in the reservoir,” explains Nina Romich. “In this way, the reservoir water always remains in a closed circuit. It has been stored in the reservoir for thousands of years and is very salty,” she says.

“With geothermal energy, it’s like with oil and gas, we don’t actually search for it directly, but we look for deposits and for certain rocks,” says Philipp Strauss. And he means that literally: “First, a geological study is made of a region, based on all the data already available. But we also go into the field, take samples and analyze the conditions on site.” This is followed by seismologic studies and an exploration well. Depending on the region, the hot water we are looking for is at depths of about 3,000 to 4,000 meters. As a comparison, oil and gas in the Vienna Basin can already be extracted from depths as shallow as of 1,000 to 1,500 meters.

The geothermal energy can be used, for example, to generate electricity by means of a steam turbine. “At the moment, this is only economically feasible if the extracted reservoir water reaches extraordinarily high temperatures in countries like Iceland, New Zealand or Italy . In the Vienna Basin, for example, we get a lower surface temperature, so a lot of efficiency would be lost,” says Nina.

The geothermal conditions in the Vienna Basin, however, are very well suited for use as a direct heat carrier for district heating. “For this, you need the right infrastructure – i.e., a district heating network or an industrial consumer such as a factory – in the immediate vicinity of the drilling site, because you can’t store heat for a long time or transport it over long distances,” says Nina Romich. “Here’s a comparison: I can feed electricity into the grid immediately, there is a power line almost everywhere. This is more difficult with district heating, because the grids are not developed over such a large area – and that has to be taken into account when looking for locations for geothermal projects,” explains Philipp Strauss.

“The industrial application of geothermal energy is still in its infancy,” says Philipp Strauss. “There’s huge potential in questions like how to build heat exchangers on an industrial scale or whether electricity generation is possible even at low temperatures. A lot is set to happen here in the next couple of years,” he says. 

OMV has included geothermal energy in its new strategy: The plan is to produce up to 9 TWh of energy per year from geothermal applications by 2030, making another important contribution to reducing CO2. “In addition to the Vienna Basin, we are also evaluating the geothermal potential in many other regions,” says Nina Romich. 

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