Contact
| Phone | +41 44 632 2558 |
| mohamed.mostafa(at)eaps.ethz.ch |
Administration
| Katerina Good | |
| Phone | +41 44 632 3465 |
| katerina.good(at)eaps.ethz.ch | |
Brief introduction
My research in the GEG group focuses on developing Plasma-Pulse Geo-Drilling (PPGD) technology through numerical modeling and lab experiments. PPGD has the potential to significantly reduce drilling costs in hard rock formations at depths up to 5 km or more.
Publications 
[Go to Proceedings Refereed] [Go to Proceedings Non-Refereed] [Go to Theses]
Underlined names are links to current or past GEG members
REFEREED PUBLICATIONS IN JOURNALS
5.
Ezzat, M., J. Beorner, E. Kammermann, E. Rossi, B.M. Adams, V. Wittig, J. Biela, H-O. Schiegg, D. Vogler, and M.O. Saar, Impact of Temperature on the Performance of Plasma-Pulse Geo-Drilling (PPGD), Rock Mechanics and Rock Engineering, 2024. https://doi.org/10.1007/s00603-023-03736-y [Download] [View Abstract]Advanced Geothermal Systems (AGS) may in principle be able to satisfy the global energy demand using standard continental-crust geothermal temperature gradients of 25-35◦C/km. However, conventional mechanical rotary drilling is still too expensive to cost-competitively provide the required borehole depths and lengths for AGS. This highlights the need for a new, cheaper drilling technology, such as Plasma-Pulse Geo-Drilling (PPGD), to improve the economic feasibility of AGS. PPGD is a rather new drilling method and is based on nanoseconds-long, high-voltage pulses to fracture the rock without mechanical abrasion. The absence of mechanical abrasion prolongs the bit lifetime, thereby increasing the penetration rate. Laboratory experiments under ambient-air conditions and comparative analyses (which assume drilling at a depth between 3.5 km and 4.5 km) have shown that PPGD may reduce drilling costs by approximately 17-23%, compared to the costs of mechanical drilling, while further research and development are expected to reduce PPGD costs further. However, the performance of the PPGD process under deep wellbore conditions, i.e., at elevated temperatures as well as elevated lithostatic and hydrostatic pressures, has yet to be systematically tested. In this paper, we introduce a standard experiment parameter to examine the impact of deep wellbore conditions on drilling performance, namely the productivity (the excavated rock volume per pulse) and the specific energy, the latter being the amount of energy required to drill a unit volume of rock.
We employ these parameters to investigate the effect of temperature on PPGD performance, with temperatures increasing up to 80◦C, corresponding to a drilling depth of up to approximately 3 km.
4.
Ezzat, M., B. M. Adams, M.O. Saar, and D. Vogler, Numerical Modeling of the Effects of Pore Characteristics on the Electric Breakdown of Rock for Plasma Pulse Geo Drilling, Energies, 15/1, 2022. https://doi.org/10.3390/en15010250 [Download] [View Abstract]Drilling costs can be 80% of geothermal project investment, so decreasing these deep drilling costs substantially reduces overall project costs, contributing to less expensive geothermal electricity or heat generation. Plasma Pulse Geo Drilling (PPGD) is a contactless drilling technique that uses high-voltage pulses to fracture the rock without mechanical abrasion, which may reduce drilling costs by up to 90% of conventional mechanical rotary drilling costs. However, further development of PPGD requires a better understanding of the underlying fundamental physics, specifically the dielectric breakdown of rocks with pore fluids subjected to high-voltage pulses. This paper presents a numerical model to investigate the effects of the pore characteristics (i.e., pore fluid, shape, size, and pressure) on the occurrence of the local electric breakdown (i.e., plasma formation in the pore fluid) inside the granite pores and thus on PPGD efficiency. Investigated are: (i) two pore fluids, consisting of air (gas) or liquid water; (ii) three pore shapes, i.e., ellipses, circles, and squares; (iii) pore sizes ranging from 10 to 150 μm; (iv) pore pressures ranging from 0.1 to 2.5 MPa. The study shows how the investigated pore characteristics affect the local electric breakdown and, consequently, the PPGD process.
3.
Ezzat, M., D. Vogler, M. O. Saar, and B. M. Adams, Simulating Plasma Formation in Pores under Short Electric Pulses for Plasma Pulse Geo Drilling (PPGD), Energies, 14/16, 2021. https://doi.org/10.3390/en14164717 [Download] [View Abstract]
Plasma Pulse Geo Drilling (PPGD) is a contact-less drilling technique, where an electric discharge across a rock sample causes the rock to fracture.
Experimental results have shown PPGD drilling operations are successful if certain electrode spacings, pulse voltages, and pulse rise times are given.
However, the underlying physics of the electric breakdown within the rock, which cause damage in the process, are still poorly understood.
This study presents a novel methodology to numerically study plasma generation for electric pulses between 200 to 500 kV in rock pores with a width between 10 and 100 \(\mu\)m.
We further investigate whether the pressure increase, induced by the plasma generation, is sufficient to cause rock fracturing, which is indicative of the onset of drilling success.
We find that rock fracturing occurs in simulations with a 100 \(\mu\)m. pore size and an imposed pulse voltage of approximately 400 kV.
Furthermore, pulses with voltages lower than 400 kV induce damage near the electrodes, which expands from pulse to pulse, and eventually, rock fracturing occurs.
Additionally, we find that the likelihood for fracturing increases with increasing pore voltage drop, which increases with pore size, electric pulse voltage, and rock effective relative permittivity while being inversely proportional to the rock porosity and pulse rise time.
2.
Horacek, J., et al., M. Ezzat, et al., EUROfusion MST1 Team, JET Contributors, and MAST-U Team, Scaling of L-mode heat flux for ITER and COMPASS-U divertors, based on five tokamaks, Nuclear Fusion, 60/6, 2020. https://doi.org/10.1088/1741-4326/ab7e47 [Download] [View Abstract]This contribution aims to improve existing scalings of the L-mode power decay length, especially for plasma configurations with strike points at the ITER-relevant location - closed vertical divertor targets. We propose 13 new scalings based on data from the tokamaks JET, EAST, MAST, Alcator C-mod and COMPASS, and validate them against the output of the 2D turbulence code HESEL. The analysis covers 500 divertor heat flux profiles (obtained by probes or IR cameras), measured in L-mode discharges with varying 12 global plasma parameters (all well predictable). We find that two previously published scalings [Eich, J.Nucl.Mat. 438 (2013) S72; Scarabosio, J.Nucl.Mat. 438 (2013) S426] (based on outer targets of AUG and JET) describe well all the JET, C-mod and COMPASS profiles, not only at outer horizontal and vertical targets, but surprisingly also at the inner vertical targets. In contrast, EAST, HESEL and especially MAST data are poorly described by these scalings. We therefore derive 13 new scalings describing 85-92 % of the measured decay lengths variability. The reader is suggested to use as many as possible scalings from here, depending on which parameters have available. Despite the fact that the scaling candidates are based on different parameters, predictions for the highest current L-modes in ITER are all very similar. Just prior to the L-H transition, in ITER baseline scenario, all the scalings predict values 2.5-3.5 mm (mapped to outer midplane), shorter for a single scaling based on predicted stored plasma energy. 1.6-2.6 mm is predicted for the COMPASS-Upgrade tokamak. In attached L-mode plasma, our results imply (using significant assumptions) steady-state surface-perpendicular heat flux around 10 MW/m2 for ITER, and 20 MW/m2 for COMPASS-Upgrade.
1.
Ascasíbar, E., et al., M. Ezzat, et al., J. M. García-Regaña, et al., and the TJ-II team, Overview of recent TJ-II stellarator results
, Nuclear Fusion, 59/11, pp. 1-13, 2019. https://doi.org/10.1088/1741-4326/ab205e [Download] [View Abstract]The main results obtained in the TJ-II stellarator in the last two years are reported. The most
important topics investigated have been modelling and validation of impurity transport, validation
of gyrokinetic simulations, turbulence characterisation, effect of magnetic configuration on
transport, fuelling with pellet injection, fast particles and liquid metal plasma facing components.
As regards impurity transport research, a number of working lines exploring several
recently discovered effects have been developed: the effect of tangential drifts on stellarator
neoclassical transport, the impurity flux driven by electric fields tangent to magnetic surfaces
and attempts of experimental validation with Doppler reflectometry of the variation of the
radial electric field on the flux surface. Concerning gyrokinetic simulations, two validation
activities have been performed, the comparison with measurements of zonal flow relaxation
in pellet-induced fast transients and the comparison with experimental poloidal variation of
fluctuations amplitude. The impact of radial electric fields on turbulence spreading in the edge
and scrape-off layer has been also experimentally characterized using a 2D Langmuir probe
array. Another remarkable piece of work has been the investigation of the radial propagation of
small temperature perturbations using transfer entropy. Research on the physics and modelling
of plasma core fuelling with pellet and tracer-encapsulated solid-pellet injection has produced
also relevant results. Neutral beam injection driven Alfvénic activity and its possible control
by electron cyclotron current drive has been examined as well in TJ-II. Finally, recent results
on alternative plasma facing components based on liquid metals are also presented.
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PROCEEDINGS NON-REFEREED
1.
Ezzat, M., J. Börner, D. Vogler, V. Wittig, B. Kammermann, J. Biela, and M. O. Saar, Lithostatic Pressure Effects on the Plasma-Pulse Geo-Drilling (PPGD), 48 EPS Conference on Plasma Physics , 2022. https://doi.org/10.3929/ethz-b-000568862 [Download] [View Abstract]Drilling cost is one of the main challenges facing the utilization of deep closed-loop geothermal systems, so-called Advanced Geothermal Systems (AGS). Plasma-Pulse GeoDrilling (PPGD) is a novel drilling technology that uses high-voltage electric pulses to damage the rock without mechanical abrasion. PPGD may reduce the drilling costs significantly compared to mechanical rotary drilling, according to a comparative analysis that assumes ambient operating conditions. However, the level of performance of PPGD under deep wellbore conditions of higher pressures and temperatures is still ambiguous. Therefore, this contribution presents preliminary experiment results from the laboratory that investigate the effect of high lithostatic pressures of up to 150 MPa, equivalent to a depth of ∼5.7 km, on the performance of PPGD.
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THESES
2.
Ezzat, M., Numerical and Experimental Investigation of the Plasma-Pulse Geo-Drilling Technology, Dissertation, ETH Zurich, pp., 2024. https://doi.org/10.3929/ethz-b-000697688 [Download] [View Abstract]The economic feasibility of harnessing deep-geothermal energy (i.e., 5 km or more) via Enhanced or Advanced Geothermal Systems is conditional on reducing the drilling costs significantly, which is unachievable using conventional mechanical rotary drilling. A game changer could lie among frictionless or contactless drilling technologies, including Plasma-Pulse Geo-Drilling (PPGD). PPGD uses microsecond-long highvoltage pulses to fracture the rock by inducing electric discharging inside it. If the resulting increase in the tensile pressure exceeds the rock’s tensile strength, PPGD fractures the rock. Intermittent research using lab experiments and numerical modeling over the last few decades has shown that PPGD can reduce drilling costs by around 20% compared to mechanical rotary drilling, while analytical estimations expect further reductions of up to 90%, assuming further research and development.
Despite that, the physics underlining the PPGD process has yet to be fully understood to optimize the operating parameters and push the PPGD research from lab experiments to field scale testing. Further, PPGD feasibility in deep drilling for deep-geothermal investments requires systematic experimental investigations of the effect of these deep wellbore extreme conditions of temperatures and lithostatic and hydrostatic pressures on the PPGD performance. The numerical modeling and the lab experiments presented in this thesis contribute to bridging these knowledge gaps, as follows. First, Chapter 1 gives a general brief background on the motivation behind the PPGD research, the working principle of the PPGD, the advantages and the challenges, and the thesis outline. The content of this chapter is brief as more elaborations are given in the introduction sections of the following Chapters 2-4.
Then, Chapter 2 investigates the impact of the pore characteristics (i.e., fluid, pressure, size, and shape) on the PPGD process. To this end, we build an electrostatic model to calculate the voltage gradient distribution across a given granite sample, thereby calculating the voltage gradient across a single pore. For PPGD to induce fracturing, these calculated voltage gradients must exceed the fluid’s dielectric strength under the defined pore size and pressure. The outcome of this chapter is an electric breakdown criteria to estimate the dielectric strength of any rock, and this criterion has been validated against experimental data.
Next, Chapter 3 investigated the impact of temperature elevation up to 80C on the PPGD process, simulating the conditions at a depth of ∼3 km. To this end, we build an experimental protocol to test the impact of temperature elevation, lithostatic pressure elevation, and hydrostatic pressure elevation on the PPGD performance. The main outcome of this chapter is that temperature alone reduces the performance of the PPGD process linearly in granite when deionized water is used, and using an alternative oil-based mud could improve the performance at high temperatures.
After that, Chapter 4 investigated the impact of lithostatic pressure elevation up to 150 MPa on the PPGD process, simulating the lithostatic pressure conditions at a depth of ∼5.7 km. Increasing the lithostatic pressure up to 40 MPa reduces PPGD performance (i.e., productivity decreases to around 60% and Specific energy increases by 75% from their baseline values), which is unfavorable for the PPGD process. Between the 40 and 80 MPa pressure values, the observed performance shows a constant value, as there is no change in the values of both the productivity and the specific energy for the given error bars. For lithostatic pressure values greater than 80 MPa, PPGD performance is enhanced significantly (i.e., productivity increased by around 60% above its baseline value and Specific energy decreased by 75%), which is favorable for the PPGD process. The effect of both temperature and lithostatic pressure has shown a tendency to enhance the performance of the PPGD process to exceed the baseline value at depths greater than 3.5 km.
Finally, Chapter 5 summarizes the thesis in two sections; the first is for the numerical modeling work of Chapter 2, while the second is for the experimental lab work of Chapters 3 and 4. Each section highlights the modeling scheme or the experimental protocol, the main findings focusing on the implications, and concludes with an outlook for future research
1.
Ezzat, M., Advanced neoclassical impurity transport modelling with its experimental comparison for TJ-II , MSc Thesis, Ghent University, 51 pp., 2018. [View Abstract]The absence of the disruptive instabilities, increasing of the confinement time with the ECRH heating and the steady-state operation make stellarator concept as a competitive candidate for future fusion reactors as the tokamak. Impurity accumulation in the core though is one of the stellarator drawbacks because it dilutes the plasma and increases the radiation losses contributing to the plasma collapse. Neoclassical theory predicts a non-ambipolar transport of different species electrons and ions in stellarators due to magnetic field ripples that are produced by the three-dimensional coils structure. Non-ambipolar transport creates, depending on the collisionality of each species, inward (outward) an ambipolar radial electric field for ion (electron) root regimes. Ion root regime has been predicted for the future stellarator reactor scenarios, which imply very likely impurity accumulation. However, outward transport has been observed during an improved confinement regime so-called \textit{HDH mode} at W7-AS (\textit{K. McCormick 2002}) and the \textit{impurity hole} at LHD (\textit{K. Ida 2009}) but without without satisfactory theoritical explanation. Historically, neoclassical treatment considers only the radial component of the electric field, which is a good approximation for the bulk species, but not for the higher charge species like impurity. Recent approaches have considered the tangential component due to the variation of the electrostatic potential within a flux surface which is more important for high charge impurity (see \[\textit{J. M. {Garc\'ia-Rega\~na} 2013}\] and reference therein). Advanced modelling of this variational part has been done here for TJ-II plasma introducing a parameter which can be measured indirectly. Direct measurement of the variational part is non-trivial and had been carried only for plasma edge (\textit{M. A. Pedrosa 2015}). Here, the indirect measurements cover the whole cross section by constructing the radiation map at two toroidal planes in TJ-II that carried impurity density distribution and in sequence the variational electrostatic part. Linearized impurity-ion collision operator (in \textit{I. Calvo 2018-Arxiv}) had been employed for impurity simulation because it is higher collisional instead of the usual pitch angel scattering operator (in \textit{C. D. Beidler 2011}) for bulk species with low collisions.