Deep U-tube heat exchanger breakthrough: combining laser and cryogenics gas for geothermal energy exploitation

The disruptive technology envisioned in the “Deep U-tube heat exchanger breakthrough: combining laser and cryogenics gas for geothermal energy exploitation (DeepU)” Project is expected to revolutionize the deep geothermal energy sector. The ultimate goal is to create a deep (>4 km) closed-loop connection in the shape of a U-tube exchanger by developing a fast and effective drilling technology. A laser drill head is combined with special drill strings sustaining the coupled action of laser and cryogenic gas, responsible for melting, evaporating and cooling even the hardest rocks. The fine particles are transported to the surface in the gas stream via the earth tube required for the geothermal heat exchanger. Specific temperature control analysis and innovative laser lenses, able to convey the heat and sustain multilateral drilling, guarantee liquefaction and vitrification of the rocks from the ground surface to significant depths. The resulting glazed layer on the borehole walls acts as a case so that the heat exchanger is ready immediately after drilling. The technical feasibility of DeepU is demonstrated at the laboratory scale, and the specific objectives of the Project are: (i) select a cryogenic gas able to cool in a controlled manner the rock melted by a laser; (ii) develop an innovative lightweight drill string able to host the gas and the laser at the same time; (iii) develop specific temperature control analysis and innovative laser lenses able to convey the heat and to sustain multilateral drilling, (iv) determine the physical-thermal phenomena affecting different kinds of rocks in order to assess the borehole wall vitrification and integrity. Numerical simulations calibrated by the laboratory data provide references to define the DeepU geothermal exploitation potential, including economic analyses. The legislative aspects and environmental standards related to the proposed solution are also assessed. The high-risk innovation presented in DeepU has the potential to make geothermal energy systems accessible anywhere in a targeted and demand-oriented manner, offering a complementary approach and an alternative solution to traditional energy storage and production, decentralizing the power supply also in areas where this is currently deemed uneconomic.