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Fast track innovative drilling system for deep geothermal challenges in Europe

Periodic Reporting for period 3 - ThermoDrill (Fast track innovative drilling system for deep geothermal challenges in Europe)

Reporting period: 2018-09-01 to 2019-08-31

Geothermal energy is a key component of Europe’s energy strategy to significantly enhance the share of renewable and sustainable energy systems in Europe. In order to make geothermal energy more attractive, there is an urgent need to provide cost-efficient and novel deep drilling technologies and concepts which increase the number of economically viable geothermal projects in Europe.

Overall objectives:
Revolutionary and breakthrough drilling technology
Geothermal wells often have to be drilled through very hard rock formations. This takes state-of-the-art drilling equipment to its limits, resulting in an urgent need for a faster and more durable technology. The combination of conventional rotary drilling with high pressure water jetting showed the potential to be the required game-changing technology. The high pressure jet cuts the rock surface in front of the drill bit, reducing the stress in the rock and thus significantly increasing the rate of penetration. The pressure is generated downhole, meaning that no additional surface infrastructure is required and high safety standards can be upheld.
Unique drill bit prototype
The drill bit needs to withstand the enormous hydraulic pressure transferred through the bit to the jetting nozzles. For this reason a novel high pressure body was designed and integrated into the frame of a roller cone bit. The extended nozzles allow quick and easy maintenance and exchange of worn-out parts, while also keeping the distance between the borehole bottom and the nozzle to a minimum.
During the ThermoDrill project period (September 2015 to August 2019), all set Milestones were achieved and all planned Deliverables successfully finalized and submitted.
Some challenging tasks such as the drill bit development and optimization, the experimental/numerical investigation of the jet cutting performance (under simulated wellbore conditions) or the development of an alternative drilling fluid have, to a large extent, already been successfully completed in the first 3 project years.
Within the 4th Project year, the consortium continued to make remarkable progress towards further optimizing the drill bit design and validating the current design by utilizing the comprehensive dataset from scaled-down and full-scale experiments. In addition, experiments and simulations via the powerful IDEASTM platform were performed and the simulation of jet-rock interaction was investigated in detail.
The research & development focus at the end of the project was on testing and optimization of the individual ThermoDrill system components as well as their proper interaction. Furthermore, significant progress was made in optimizing the Downhole Pressure Intensifier (DPI) including its subcomponents, high-pressure connections and sealing. After manufacturing, the DPI units were delivered to the project partner RED for extensive surface testing.
Due to tireless efforts of all ThermoDrill participants, the physical assembly of the DPI units in the custom-built housing and connection with the drill bit was performed without any considerable issues. After reaching this major milestone, the surface tests were performed and positively completed. During the tests, potential for further improvements were identified that required some modification of the DPI. Despite a very tight timeframe, all of the identified DPI modifications were performed in time prior to the field tests. In May 2019 the field tests were accomplished in a rather impressive manner. A three-cone bit with identical cutting structure was used for the baseline run. Drilling occurred in the same formation and at similar depth as the tests of the ThermoDrill assembly. The field tests clearly verified the feasibility and efficiency of the ThermoDrill system in real drilling environment and the observed drilling performance confirmed the significant advantages compared to the baseline bit. Moreover, the tests allowed to identify technical aspects to develop this promising technology further.
Renewable geothermal energy is low on emissions and has the potential to become an important cornerstone of base-load energy generation in Europe, either for electricity or via direct utilisation for heating of households or greenhouses. One important advantage of geothermal over other currently available renewable energy sources is its capability of providing continuous and more or less constant base-load electricity, irrespective of daytime, weather conditions or the time of the year. In principle, geothermal energy could be utilised in most parts of the globe. However, suitable geological rock formations are commonly found at great depths in the order of 4,000 to 5,000 meters below surface. Accessing such deep energy reservoirs are inherently linked to significant drilling costs that, in many instances, amount to almost half of the total capital investment costs of the entire geothermal energy plant. During borehole establishment, different geological rock formations with variable hardness and strength are penetrated. Hard rock types (e.g. granite) encountered during drilling are causing much reduced penetration rates and lead to excessive wear of the drill bit. To overcome the aforementioned issues, the ThermoDrill consortium, managed to develop a novel revolutionary drilling technology which has already been successfully deployed in field tests.

Innovative drilling technology
The novel hybrid drilling technique combines standard rotary drilling with a technology called water jet cutting. The high-pressure water jet (approx. 2,000 bar) is used to pre-damage the rock on impact with the effect of significantly increasing the rate of penetration and thus the overall efficiency of the drilling process. Technical, economic and safety reasons demand that the high-pressure generation unit is directly placed below the drill bit. Despite several great challenges including confined space and harsh conditions at the borehole bottom, a prototype of the high-pressure generation unit was developed and successfully integrated as essential component of the ThermoDrill drilling system.

Novel technology successfully tested
The feasibility and efficiency of the innovative drilling technology was initially tested in experiments at various laboratory scales. Final field tests under real environment within an existing 1,3 km deep borehole confirmed the enormous potential of the technology, which is capable of achieving around twice the rate of penetration when compared to standard rotary drilling. Moreover, the tests highlighted that the novel “ThermoDrill-System” can be integrated with existing drilling infrastructure and technology without any difficulties, thereby boosting the acceptance for its deployment as a market-ready system in future.

Significant cost-reductions for geothermal drilling
As previously mentioned, a considerable reduction of the drilling costs leads to substantially reduced overall capital expenditure, hence to much improved economics of entire geothermal projects. Via the deployment of the “ThermoDrill-System”, cost savings of approx. 20% or around 3 Million Euro are expected to be achieved, just for a single deep borehole (5,000 m). Further future advancements will bring this drilling technology to market-readiness, thereby paving the way for intensified utilisation of geothermal as environmentally friendly alternative energy source throughout Europe and even globally.
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