Mohamed Ezzat


Last Name

Ezzat

First Name

Mohamed

ORCID

0000-0001-9894-009X

Organisational unit

09494 - Saar, Martin O. / Saar, Martin O.

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2020 - 202412
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Publications 1 - 10 of 12
  • Numerical Modeling to Study the Impact of Pore Characteristics on the Electric Breakdown of Rock for Plasma Pulse Geo Drilling (PPGD)
    Item type: Other Conference Item
    Ezzat, Mohamed; Vogler, Daniel; Adams, Benjamin; et al. (2021)
    Reducing the cost of drilling is crucial to economically extract deep geothermal energy as drilling costs can reach up to 70% of the total investment budget (Tester et al. 2006). Unfortunately, traditional mechanical rotary drilling is often far too expensive to enable economical geothermal energy extraction from many deep geologic settings due to the amount of energy rotary drilling requires and due to its significant drill bit wear, causing long, unproductive tripping times to exchange worn drill heads (Schiegg et al. 2015). To reduce deep geothermal drilling costs, novel drilling technologies are required, such as Plasma Pulse Geo Drilling (PPGD) as well as thermal spallation, laser, and microwave drilling, to name a few (Woskov et al. 2014; Buckstegge et al. 2016; Vogler et al. 2020; Walsh et al. 2020). PPGD is a so-called contact-less drilling technology that uses high-voltage electricity pulses >200 kV that last for ∼2 microseconds to fracture the rock, thereby drilling without mechanical abrasion, reducing/eliminating costly, unproductive tripping times and requiring less energy to break the rock than rotary drilling. Experimentally, Anders et al. 2017 found that PPGD is ∼17% cheaper than mechanical rotary drilling. Analytical studies by Rodland 2012 and Schiegg et al. 2015 suggested that further research could possibly reduce PPGD drilling costs by as much as ∼90% of current mechanical rotary drilling costs. Nonetheless, the fundamental physics that underlies the PPGD process is still poorly understood, and the feasibility of PPGD under deep wellbore conditions requires further investigations. (Zhu et al. 2021) investigated numerically how the local electric breakdown in pores can lead to electric breakdown occurrence across the entire rock sample. Numerically, Ezzat et al. 2021 found that the plasma pressure generated due to the localized electric breakdown in rock pores is high enough to induce rock fracturing for specific conditions, resulting in drilling success. Here, we present our preliminary numerical modeling results concerning the influence of rock pore characteristics, such as pore fluid, shape, and size on the localized electric breakdown of rock. Our goal is to eventually use these results to further increase the efficiency, and thus, further reduce the costs, of PPGD. Our results show that PPGD is facilitated if the rock pores are filled with a gas and not with water, which is consistent with the experimental findings of Lisitsyn et al. 1998 and Inoue et al. 1999. Also, our results suggest that larger pore sizes and smaller pore pressures are more favorable for PPGD. These findings are valid until ∼1 MPa pore pressure. To extend our model to cover higher pressure ranges, further physical lab experiments are required that investigate the electric breakdown of air at high gas pressures >1 MPa.
  • How Plasma-Pulse Geo-Drilling (PPGD) can make Geothermal Energy Cheaper
    Item type: Presentation
    Ezzat, Mohamed (2022)
  • Simulating plasma formation in pores under short electric pulses for plasma pulse geo drilling (Ppgd)
    Item type: Journal Article
    Ezzat, Mohamed; Vogler, Daniel; Saar, Martin O.; et al. (2021)
    Energies
    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 and 500 kV in rock pores with a width between 10 and 100 µm. 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 µm 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.
  • Impact of Temperature on the Performance of Plasma-Pulse Geo-Drilling (PPGD)
    Item type: Journal Article
    Ezzat, Mohamed; Börner, Jascha; Kammermann, Benedikt; et al. (2024)
    Rock Mechanics and Rock Engineering
    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 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 PPGD performance, namely the productivity (the excavated rock volume per pulse) and the specific energy (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.
  • Numerical Modeling to Study the Impact of Pore Characteristics on the Electric Breakdown of Rock for Plasma Pulse Geo Drilling (PPGD)
    Item type: Other Conference Item
    Ezzat, Mohamed; Vogler, Daniel; Adams, Benjamin; et al. (2021)
  • Lithostatic Pressure Effects on the Plasma-Pulse Geo-Drilling (PPGD)
    Item type: Conference Paper
    Ezzat, Mohamed; Börner, Jasch; Vogler, Daniel; et al. (2022)
    48th EPS Conference on Plasma Physics
    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 Geo- Drilling (PPGD) is a novel drilling technology that uses high-voltage electric pulse to dam- age 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 well- bore 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.
  • On the effects of the lithostatic, hydrostatic pressures, and the temperature on Plasma Pulse Geo Drilling (PPGD)
    Item type: Other Conference Item
    Ezzat, Mohamed; Börner, Jascha; Vogler, Daniel; et al. (2022)
    InterPore 2022 Book of Abstracts
  • Plasma Pulse Geo-Drilling as a Low-cost Drilling Technology for Deep-geothermal Energy Utilization: Status and Challenges
    Item type: Other Conference Item
    Ezzat, Mohamed; Börner, Jascha; Vogler, Daniel; et al. (2022)
    EGUsphere
    Geothermal energy can be a limitless and CO2-free energy resource. However, moderate geothermal temperature gradients of ∼30 oC/km in most regions typically require employing so-called "Advanced" or "Enhanced" geothermal systems, called AGS and EGS, respectively, which require reservoirs with temperatures >150 oC. To access such high temperatures, we need to drill deeper than 5 km, i.e., in hard rock. The costs of drilling to such depths, using traditional rotary drilling, increase exponentially with depth and can be up to 80% of the total geothermal project investment. These high drilling costs can be reduced significantly with contactless drilling technologies (e.g., thermal spallation drilling, laser drilling, microwave drilling, and Plasma Pulse Geo-Drilling), as they avoid the lengthy tripping times associated with drill-bit damage. PPGD uses high-voltage pulses of a few microseconds duration to fracture the rock, thereby drilling without any mechanical abrasion. Future PPGD costs may be as low as 10% of mechanical rotary drilling costs (Schiegg et al., 2015). Our PPGD research addresses two outstanding questions: (1) Understand the fundamental physics of the electric breakdown inside the rock and associated rock fracturing processes, which we investigate numerically (Ezzat et al., 2022, 2021; Vogler et al., 2020; Walsh and Vogler, 2020). (2) Evaluate the PPGD performance under deep-wellbore conditions of ~5 km (i.e., high pore and lithostatic pressures, and high temperatures). Our ongoing numerical and experimental studies are expected to provide further insights into the applicability of PPGD for geothermal energy utilization. First, we numerically model the formation of a plasma in rock pores, which constitutes the onset of rock failure during the PPGD process. These numerical models show the significant effect of the pore characteristics on the PPGD process and give insight into how future PPGD operations should be designed. Second, we conduct PPGD physical experiments, where we employ lithostatic pressures of up to 1500 bar, pore pressures of up to 500 bar, temperatures of up to 80 oC, and voltages of up to 300 kV. Concluding these experiments with the associated challenges shall demonstrate whether PPGD is efficient at great depths of up to 5 km. Combining our numerical and experimental results allows optimizing future PPGD operations.
  • Plasma-Pulse Geo-Drilling for Geothermal Energy
    Item type: Other Conference Item
    Ezzat, Mohamed; Börner, Jascha; Vogler, Daniel; et al. (2022)
  • Numerical Modeling of the Effects of Pore Characteristics on the Electric Breakdown of Rock for Plasma Pulse Geo Drilling
    Item type: Journal Article
    Ezzat, Mohamed; Adams, Benjamin; Saar, Martin O.; et al. (2022)
    Energies
    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.
Publications 1 - 10 of 12