High-power fibre laser used to weaken hard rock in geothermal drilling

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A high-power fibre laser has been successfully tested in field trials for weakening hard rock in order to improve the efficiency and cost of geothermal drilling, a process used to access geothermal heat – a clean and sustainable energy source.

When drilling deep into the earth's crust, not only does the temperature of a drill bit rise by an average of about three degrees Celsius per 100 metres, but when hard rock is encountered, the drill bit wears more quickly and its rate of penetration decreases. The cost of this can be prohibitive, and frequently prevents investors from going ahead with deep geothermal projects.

Scientists from the Fraunhofer Institute for Production Technology IPT have therefore joined forces with partners of the research project ‘LaserJetDrilling’, to develop a method for laser-assisted mechanical drilling of hard rock – a technique that could not only increase the rate of penetration of geothermal drilling, but also help preserve the cutting edge of the drill bit by weakening and even fracturing the rock immediately before the drilling commences.

The scientists developed the technique by initially setting up a test rig with an ytterbium fibre laser from IPG Photonics with an output power of up to 30 kilowatts, which they then used to successfully weaken sandstone, granite and quartzite  all of which are hard rocks with a strength of more than 150 megapascals – by up to 80 per cent. A water-jet was used to guide the laser beam to the rock face – similar to how an optical fibre is able to guide a laser – which also prevents contamination and damage to the sensitive laser optics and facilitates the removal of the rock debris by the drilling tool. In the next step, engineers used the laser on the drilling rig in a specially developed drill string and, in collaboration with the International Geothermal Centre Bochum, tested the new tool under realistic conditions in field trials, which also proved to be a success.

The Fraunhofer IPT scientists set up a rig with a 30kW ytterbium fibre laser to test the method on hard rocks such as sandstone, granite and quartzite (Image: Fraunhofer IPT)

In future research projects, the partners intend to further enhance the distribution of the laser power and add digital sensors to the hybrid tool in order to obtain feedback from the drilling process and thus to be able to react to changes in material along the drilling path. The flexible adjustment of the output power of the laser is one of the factors that make it a particularly efficient tool for assisting drilling processes.

According to the project partners, the developed powerful drilling system will help to reduce the cost of deep geothermal drilling in the future and increase the ease with which geothermal energy can be exploited as an inexhaustible energy source – supporting other renewable sources such as sunlight, wind and water.

The consortium of the LaserJetDrilling project consists of entities Fraunhofer IPT, IPG Laser, Swiss firm Synova – an expert in the use of water to guide laser beams, The International Geothermal Centre Bochum, drilling rig manufacturer Herrenknecht Vertical and high-pressure pump manufacturer Kamat Pumpen. The project was funded by the Federal Ministry for Economics Affairs and Energy (BMWi).

Top image caption: A high power laser, guided by a water jet, has been used to weaken hard rock prior to geothermal drilling.

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