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

Periodic Reporting for period 1 - DeepU (Deep U-tube heat exchanger breakthrough: combining laser and cryogenic gas for geothermal energy exploitation)

Période du rapport: 2022-03-01 au 2023-02-28

The disruptive technology envisioned in “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 are: (i) to select a cryogenic gas able to cool in a controlled manner the rock melted by a laser; (ii) to develop an innovative lightweight drill string able to host the gas and the laser at the same time; (iii) to develop specific temperature control analysis and innovative laser lenses able to convey the heat and to sustain multilateral drilling, (iv) to 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.
The DeepU project consists of 7 work packages (WPs): five (WP1 to WP5) address the technological and scientific development of the project, while the remaining two concern dissemination and communication (WP6) and management (WP7). DeepU is expected to achieve technical and environmental/standardization innovation goals. So far, the main results achieved are:
• WP1: definition and selection of the cryogenic gas to be used in laboratory tests (T1.1); design and modelling of 3 different laser drill string solutions (T1.2) including the design and manufacturing of the first prototype to be used in laboratory (T1.3);
• WP2: prototype of the processing drilling head (T2.1) and experimental set-up for the laboratory testing completed (T2.2); the interaction between the laser and the rock samples started (T2.3);
• WP3: beginning of rock samples petrophysical characterization after receiving the first materials (T3.1). A methodological approach is finalized and the preliminary rocks’ thin sections are now ready to be analyzed.
• WP4: review of the legislative and regulatory assessment focusing on risk management, drilling practices and underground energy storage in Europe completed (T4.1); preliminary definition of 2 main tools for the EHS evaluation (T4.2).
• WP5: silent in the first year. However, the discussion about the criteria for selecting 2 virtual case studies in Italy and Ireland started (T5.1). In addition, material on the state of art drilling cost breakdown was collected (T5.2) and the first step towards patentability of DeepU technology started to be considered (T5.3).
• WP6: the project website, logo, leaflet and brochure were completed (T6.2) as the first Dissemination, Exploitation and Communication activities Plan (T6.1). The DeepU first scientific results started to be presented at international and national congresses (T6.3).
• WP7: the Quality Assurance Plan, the Detailed Project Management Plan, the Data Management Plan and its update were prepared on time (T7.1 T7.2). 3 General Assembly meetings, 3 internal WPs meetings and 2 joint WPs meetings were held in the first year to clarify some technical procedures between WPs.
Continuously renewable, CO2-neutral, clean, affordable, and modern energy for the benefit of all people is the 7th of the United Nations Sustainable Development Goals (SDG). In addition, the EU Renewable Energy Directive and the REPowerEU plan set a common target (32%) of renewable energy in the EU’s energy consumption by 2030. Geothermal energy (GTE), defined as the thermal energy stored in the earth, is considered a critical renewable energy source for the future. Today’s installed geothermal capacity accounts for less than 1% of global geothermal resources and is expected to grow steadily until 2050. Cost reduction and improved system performance, as a new drilling technology economically and technologically more efficient than the current ones, is crucial for GTE growth.
GTE plays a key role in the energy transition towards renewables as it offers a continuous and flexible production. Therefore, increasing the GTE share in the energy mix is fundamental to develop national and European energy policies. Geothermal resources are conventionally divided into near-surface (shallow) and deep. However, current deep geothermal technologies suffer limitations and disadvantages, among them the depth limitation (4-5km) due to the traditional drilling methods.
To overcome these limits and make projects economically viable, the DeepU technology focuses on demonstrating at the lab scale a U-shaped closed-loop system, physically isolated from the surrounding environment. With a new, revolutionary, intelligent temperature management control system tested in laboratory, the project will use a laser-beam propulsion drilling method and a cryogenic gaseous flushing medium to realize a heat exchanger consisting of two vertical and one horizontal tube section (U-shape). The use of laser & cryogenic gas will form a glazed layer on the borehole walls, allowing an underground closed-loop system to immediately develop after drilling without requiring further casing activities. This technical solution will also favor the gravity pump effect during geothermal exploitation. If successful, the DeepU technological could contribute to realizing ultra-deep geothermal heat exchangers at >4km depth.
The laser beam on the rock sample before starting the drilling operation