A high-power fiber laser has been successfully tested in field trials to weaken hard rocks to increase efficiency and reduce the cost of geothermal drilling. The fiber laser technology promotes a process applied to access geothermal heat — a clean and sustainable energy source.
The thing is that when drilling deep into the earth’s crust is performed, the temperature of the drill bit not only increases on average by about three degrees Celsius per 100 meters but also when it collides with a hard stone, the drill bit wears out faster and the speed of its penetration decreases.
The cost of this process can be extremely high, and often prevents investors from continuing with deep geothermal projects. Therefore, a group of researchers from Germany combined with partners on a research project to develop a method for mechanical drilling of hard rocks employing a laser system.
This fiber laser system can not only increase the penetration rate in geothermal drilling but also helps to maintain the cutting edge of the drill bit by loosening and even breaking the rock just before drilling begins.
To be more precise, the researchers have developed this laser system by initially installing a test unit with a ytterbium-based fiber laser with an output power of up to 30 kilowatts, which they then used to successfully loosen sandstone, granite, and quartzite. At the same time, all these materials are solid rocks with a strength of more than 150 megapascals — up to 80 percent.
A jet of water is used to direct the laser beam to the rock surface – similar to how optical fiber can direct a laser system— which also prevents contamination and damage to sensitive fiber laser optics and makes it easier to remove rock fragments with a drilling tool.
Then the engineers use a fiber laser system on the rig in a specially designed drill string and test the new tool in real-world conditions in field tests, which also proved successful. In future research projects, the researchers plan to further improve the laser beam power distribution and add digital sensors to the hybrid tool to get feedback from the drilling process and thus be able to respond to material changes on the drilling path.
The flexible adjustment of the laser beam output power is one of the factors that make it a particularly effective tool for facilitating drilling processes. According to the researchers, the developed powerful fiber laser system will help reduce the cost of deep geothermal drilling in the future and simplify the use of geothermal energy as an inexhaustible source of energy-supporting other renewable sources such as sunlight, wind, and water.
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