30 May 2022 to 2 June 2022
Asia/Dubai timezone

On the effects of the lithostatic, hydrostatic pressures, and the temperature on Plasma Pulse Geo Drilling (PPGD)

30 May 2022, 16:20
15m
Oral Presentation (MS17) Thermal Processes, Thermal Coupling and Thermal Properties of Porous Media: modeling and experiments at different scales MS17

Speaker

Mohamed Ezzat (Geothermal Energy and Geofluids group, ETH-Zurich)

Description

Geothermal energy is, in principle, a limitless energy resource that exists everywhere. Geothermal energy can be used as a baseload power source (i.e., it is available at all hours of the day throughout the year) or as a dispatch power source (i.e., it can support other intermittently available energy sources, such as wind and solar, by providing power when there is no wind or sunshine). However, producing heat or generating electricity from geothermal reservoirs, employing so-called "advanced"[1] or "enhanced"[2] geothermal systems, requires deep drilling into rock layers (i.e., crystalline basement) that exhibit temperatures ≳150$^o$C[3]. For example, drilling to depths of 5 km is required in Europe to reach the required temperatures (≳150$^o$C), given that the geothermal temperature gradient is typically ≲30$^o$C/km.

Drilling costs, particularly into crystalline basement rock, can contribute up to 80% of the total investment required for a geothermal power plant when using mechanical rotary drilling, which can render such power plants uneconomical. High drilling costs can be attributed to long tripping times, which is the time spent replacing worn or damaged drill bits once the often short lifetime of a drill bit has been exceeded. Contactless drilling methods, however, do not rely on mechanical abrasion, thereby eliminating mechanical abrasion and extending the lifetime of the drill bit[4–7]. Plasma Pulse Geo Drilling (PPGD) in particular uses high voltage pulses that last for a few microseconds to fracture the rock[8–12]. During PPGD, two electrodes transmit these pulses to the rock surface, inducing plasma formation inside the rock pores, increasing the pore pressure, exceeding the rock tensile strength, and causing rock fracturing. Under ambient conditions, PPGD has proven to be cheaper than mechanical rotary drilling, and further research and development could reduce the cost by 90%, compared to rotary drilling costs[3,13]. Nonetheless, no experimental work on PPGD drilling investigates deep well pore conditions, i.e., high lithostatic pressures, hydrostatic pressures, and temperatures.

This study aims at understanding the effect of the aforementioned conditions on the following five parameters: (1)PPGD performance (i.e., excavated rock volume per electric pulse); (2)Specific excavation energy (i.e., required energy to excavate a unit volume of the rock); (3)Cutting size (i.e., rock fragment size resulting from PPGD drilling); (4)Relative penetration depth (i.e., the penetration depth per unit inter-electrode gap distance); and (5)Pre-damage phase of the PPGD process.
The experimental design uses a bi-axial cell that can apply lithostatic pressure of up to 150MPa (i.e., simulating 5 km deep conditions) on a granite specimen(Figure 1a). Deionized water immerses the entire experiment setup, i.e., simulating the drilling fluid. Next, a few dozen electric pulses of 200kV, with rise-times shorter than 0.5 microseconds, are applied to the specimen. To investigate the effect of hydrostatic pressure and of temperature, rock specimens are placed in the so-called i.BOGS autoclave(Figure-1b). Pressures up to 50 MPa and temperatures up to 80$^o$C can be reached in the i.BOGS. The results of these experiments shed light on the viability of the PPGD process as a deep drilling technology and highlight the key factors driving PPGD drilling success.

References

[1] Adam E Malek, Benjamin Adams, Edoardo Rossi, Hans O Schiegg, and Martin O Saar. Electric power generation, specific capital cost, and specific power for advanced geothermal systems (ags). In 46th Workshop on Geothermal Reservoir Engineering, 2021.
[2] Valentin S. Gischig, Domenico Giardini, Florian Amann, Marian Hertrich, Hannes Krietsch, Simon Loew, Hansruedi Maurer, Linus Villiger, Stefan Wiemer, Falko Bethmann, Bernard Brixel, Joseph Doetsch, Nima Gholizadeh Doonechaly, Thomas Driesner, Nathan Dutler, Keith F. Evans, Mohammadreza Jalali, David Jordan, Anniina Kittilä, Xiaodong Ma, Peter Meier, Morteza Nejati, Anne Obermann, Katrin Plenkers, Martin O. Saar, Alexis Shakas, and Benoît Valley. Hydraulic stimulation and fluid circulation experiments in underground laboratories: Stepping up the scale towards engineered geothermal systems. Geomechanics for Energy and the Environment, 24:100175, 2020.
[3] Hans O Schiegg, Arild Rødland, Guizhi Zhu, and David A Yuen. Electro-pulse-boring (epb): Novel super-deep drilling technology for low cost electricity. Journal of Earth Science, 26(1):37–46, 2015.
[4] Daniel Vogler, Stuart DC Walsh, Philipp Rudolf von Rohr, and Martin O Saar. Simulation of rock failure modes in thermal spallation drilling. Acta Geotechnica, pages 1–14, 2020.
[5] E. Rossi, M. A. Kant, C. Madonna, M. O. Saar, and P. Rudolf von Rohr. The effects of high heating rate and high temperature on the rock strength: Feasibility study of a thermally assisted drilling method. Rock Mechanics and Rock Engineering, 51(9):2957–2964, Sep 2018.
[6] Frederik Buckstegge, Theresa Michel, Maik Zimmermann, Stephan Roth, and Michael Schmidt. Advanced rock drilling technologies using high laser power. Physics Procedia, 83:336 – 343, 2016.
[7] Paul P. Woskov, Herbert H. Einstein, and Kenneth D. Oglesby. Penetrating rock with intense millimeter-waves. In 2014 39th International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz), pages 1–2, 2014.
[8] AA. Vorob’ev, GA. Vorob’ev, and AT. Chepikov. Regularities of breakdown of a solid dielectric at the interface with a liquid dielectric under the action of a voltage pulse. Vyshaya Shkola Moscow, Dec 1961. Certificate of the opening of NA-122 (in Russian).
[9] Igor V Timoshkin, John W Mackersie, and Scott J MacGregor. Plasma channel miniature hole drilling technology. IEEE Transactions on plasma science, 32(5):2055–2061, 2004.
[10] Daniel Vogler, Stuart DC Walsh, and Martin O Saar. A numerical investigation into key factors controlling hard rock excavation via electropulse stimulation. Journal of Rock Mechanics and Geotechnical Engineering, 12(4):793–801, 2020.
[11] Stuart DC Walsh and Daniel Vogler. Simulating electropulse fracture of granitic rock. International Journal of Rock Mechanics and Mining Sciences, 128:104238, 2020.
[12] Mohamed Ezzat, Daniel Vogler, Martin O. Saar, and Benjamin M. Adams. Simulating plasma formation in pores under short electric pulses for plasma pulse geo drilling (ppgd). Energies, 14(16), 2021.
[13] E. Anders, Matthias Voigt, Franziska Lehmann, and Margarita Mezzetti. Electric impulse drilling: The future of drilling technology begins now. In 36th International Conference on Ocean, Offshore & Arctic Engineering, volume 8, Trondheim, Norway, 2017. OMAE.

Participation In person
Country Switzerland
MDPI Energies Student Poster Award Yes, I would like to submit this presentation into the student poster award.
Time Block Preference Time Block A (09:00-12:00 CET)
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Primary author

Mohamed Ezzat (Geothermal Energy and Geofluids group, ETH-Zurich)

Co-authors

Mr Jascha Börner (Fraunhofer Institution for Energy Infrastructures and Geothermal Systems (IEG) ) Dr Daniel Vogler (Geothermal Energy and Geofluids Group, Institute of Geophysics, Department of Earth Sciences, ETH Zurich) Mr Wittig Volker (Fraunhofer Institution for Energy Infrastructures and Geothermal Systems (IEG)) Prof. Martin O. Saar (Geothermal Energy and Geofluids Group, Institute of Geophysics, Department of Earth Sciences, ETH Zurich)

Presentation materials