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

Project Information

DeepU

Grant agreement ID: 101046937

DOI

10.3030/101046937

Project closed

EC signature date 7 March 2022

Start date 1 March 2022

End date 31 October 2025

Funded under

• The European Innovation Council (EIC)

Total cost

€ 3 425 640,75

EU contribution

€ 3 425 640,75

Coordinated by

R.E.D. SRL
Italy

Periodic Reporting for period 2 - DeepU (Deep U-tube heat exchanger breakthrough: combining laser and cryogenic gas for geothermal energy exploitation)

Reporting period: 2023-03-01 to 2025-10-31

Summary of the context and overall objectives of the project

The disruptive technology envisioned in the project “Deep U-tube heat exchanger breakthrough: combining laser and cryogenics gas for geothermal energy exploitation (DeepU)” aims to revolutionise the deep geothermal energy sector. The goal is to create a deep (>4 km) closed-loop U-tube heat exchanger by developing a fast and effective drilling technology. A laser drill head is connected to a special drill strings sustaining the coupled action of laser and cryogenic gas, which breaks-up, melts, evaporates and cools even the hardest rocks. Fine particles are transported to the surface in the gas stream. The gas stream also cools the borehole walls. The resulting glazed layer on the borehole walls acts as a casing so that the heat exchanger is ready immediately after drilling.
At laboratory scale, the feasibility of DeepU is demonstrated on different rock types, and the specific objectives are to: (i) select a cryogenic gas able to cool in a controlled manner the rock melted by a laser; (ii) simulate the gas flow inside and outside the drill string to predict temperature, pressure and flow rate; (iii) develop an innovative lightweight drill string able to host gas and laser simultaneously; (iv) develop temperature-control and laser lenses able to convey heat and sustain multilateral drilling; (v) determine the thermo-physical phenomena affecting different rocks, to assess borehole-wall vitrification, integrity and hydraulic tightness; (vi) evaluate legislative aspects and potential environmental, health and safety risks; (vii) model the DeepU geothermal exploitation potential for selected virtual case studies, including techno-economic analysis; (viii) assess stakeholder interest in moving from laboratory to field validation and explore market applications.
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 to traditional energy storage and production and enabling decentralised low-carbon heat supply even in areas where deep geothermal exploitation is currently deemed uneconomic.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Since the start of the project, DeepU has implemented all technical and management work packages (WP1–WP8) and completed the planned deliverables following the approved amendments and project extension.
In WP1, liquid nitrogen (LN2) was selected as reference cryogenic fluid, the DeepU operating window was defined and several drill string prototypes were designed, manufactured and tested. WP2 delivered combined laser–gas processing heads for vertical and horizontal drilling and a large-scale laboratory facility, demonstrating laser drilling in different lithologies, producing a scaled U-tube in rock and optimising key process parameters. In WP3, representative rocks were characterised before and after laser–gas exposure, confirming the formation of a vitrified wall and providing thermodynamic models that map efficient drilling and vitrification regimes. WP4 completed the legislative and standards review, carried out a detailed Failure Mode and Effect Analysis and Environment, Healthy and Safety risk assessment and produced EHS/regulatory recommendations and a technology roadmap for regulatory approval in future field demonstrations. WP5 developed numerical models of DeepU-based closed-loop systems for three virtual case studies, a drilling-operations cost estimator and techno-economic analyses, feeding into an exploitation and IPR strategy and the preparation of two patent applications. WP6 implemented and updated the PDEC, maintained the website and communication kit and disseminated results through conferences, webinars, a Final Conference and media outputs. WP7 ensured coordination, governance, quality assurance and reporting, updated the QAP and DMP (including final FAIR status) and managed the widening phase with WUST. WP8 focused on the cryogenic circulation and return-flow system and on integrated drill-string behaviour, defining return-gas flow conditions and validating the prototype drill-string assemblement.
Overall, these activities demonstrated the feasibility of the DeepU concept at laboratory scale, produced key components to around TRL 3–4 and provided a scientific, technical and regulatory basis for future field-scale demonstrations.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Continuously renewable, CO2-neutral, clean, affordable and modern energy for the benefit of all people is at the core of SDG7. In parallel, the EU Renewable Energy Directive and the REPowerEU plan set ambitious targets for the share of renewables in the EU energy mix. Geothermal energy, defined as the thermal energy stored in the Earth, is a key candidate to provide secure, low-carbon baseload heat and power. Yet, today’s installed geothermal capacity exploits less than a tiny fraction of the global resource, mainly because deep wells in hard rocks remain expensive and risky to drill with conventional rotary technologies. Current deep geothermal technologies are constrained by depth (typically 4–5 km), long drilling times, complex drilling fluids, multiple casing and cementing stages and significant non-productive time. To overcome these limits and improve the techno-economic performance of deep systems, DeepU focuses on demonstrating, at laboratory scale, a U-shaped closed-loop system physically isolated from the surrounding environment. The project combines a high-power laser with a cryogenic gaseous flushing medium (liquid nitrogen), an innovative multi-pipe drill string and dedicated processing heads to create a heat exchanger consisting of two vertical and one horizontal section (U-shape). Experiments and modelling carried out in the different work packages show that, under appropriate conditions, laser and cryogenic gas can jointly remove, melt and vitrify rock, forming a glazed layer on the borehole wall with low permeability and good mechanical integrity. This would enable an underground closed-loop system to be operated immediately after drilling, without conventional casing, and could also support favourable gravity-driven circulation during exploitation. If successfully scaled up beyond the laboratory, the DeepU technology could contribute to the realisation of ultra-deep geothermal heat exchangers at depths greater than 4 km, making “geothermal anywhere” a realistic option and supporting EU climate-neutrality and energy-transition objectives

The laser beam on the rock sample before starting the drilling operation