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German institute in geothermal tech world first

LIAG first to use 3D seismic survey to find deep petrothermal hotspots for geothermal sites

LIAG’s study could be a major development for geothermal energy

A German geophysics institute will use 3D seismic survey technology to explore geothermal reservoirs. The Leibniz Institute for Applied Geophysics (LIAG) project in Saxony, Germany, will be the first to use these techniques to locate petrothermal sites. The study could be a major step in moving on geothermal energy developments around the world.

Most geothermal power is hydrothermal, using existing hot water in rock formations. Petrothermal sites are porous but with no water, such as dry fractures or fissures. The water must be pumped through to be heated and the energy then extracted.

The project is the first of its kind to locate naturally occurring porosity at great depth. At existing petrothermal plants the heat available is shallow, but in Germany it is necessary to drill to 5 or 6km before the energy can be exploited.

LIAG said: “Our research is focussed on the petrothermal concept, or hot-dry-rock technique. This means we are searching for hot areas (100-150°C) at depth with some natural porosity where water can circulate. In this respect it is a pilot project on the world-wide scale. Of course, it may be applied elsewhere in the world. However, we expect that further development of the petrothermal technique will depend to a high degree on the results of our study.”

LIAG will identify petrothermal reservoirs using a 3D seismic survey alongside a seismic blasting “star”.

LIAG said the 3D seismic survey will be performed on an area of 10 km by 10 km size. The area consists of receiver-lines and seismic sources placed perpendicular to one another. The seismic source is a group of three heavy vibrators each weighing 27 tonnes, which emit vibrations of 10 seconds in length and 10 to 100 cycles per second frequency.

The 3D survey will allow vertical analysis, with the rays being sent on a vertical plane. Since many of the fractures will be steep, to get a complete picture horizontal rays are needed. This is the role of the seismic star.

“We designed an additional seismic experiment which applies and records seismic waves that are transmitted predominantly on horizontal wave paths through our target region at 5 to 6km depth. The seismic source in this case is an explosive charge in a borehole of 30m depth,” the LIAG said.