Pulsed Power Plasma Stimulation: A Comprehensive Review and Field Insights

Abstract

Pulsed Power Plasma Stimulation (3PS) represents a promising and environmentally favorable alternative to conventional well stimulation techniques for enhancing subsurface permeability. This comprehensive review tracks the evolution of plasma-based rock stimulation, offering insights from key laboratory, numerical, and field-scale studies. The review begins with foundational electrohydraulic discharge concepts and progresses through the evolution of Pulsed Arc Electrohydraulic Discharge (PAED) and the more advanced 3PS systems. High-voltage, ultrafast plasma discharges generate mechanical shockwaves and localized thermal effects that result in complex fracture networks, particularly in tight and crystalline formations. Compared to conventional well stimulation techniques, 3PS reduces water use, avoids chemical additives, and minimizes induced seismicity. Laboratory studies demonstrate significant improvements in permeability, porosity, and fracture intensity, while field trials show an increase in production from oil, gas, and geothermal wells. However, 3PS faces some limitations such as short stimulation radii and logistical constraints in wireline-based delivery systems. Emerging technologies like plasma-assisted drilling and hybrid PDC–plasma tools offer promising integration pathways. Overall, 3PS provides a practical, scalable, low-impact stimulation approach with broad applicability across energy sectors, especially in environmentally sensitive or water-scarce regions.

1. Introduction

Two of the key challenges current energy systems have to solve are satisfying the rising global need for energy and minimizing their environmental effects. As the world evolves toward a more sustainable energy system, subsurface engineering, especially rock fracturing, becomes more vital. Numerous critical industries are currently supported by engineered rock fractures. For instance, more than 95% of oil and gas extraction from unconventional shale formations [1,2], as well as 80 to 90% of Enhanced Geothermal Systems (EGSs) [3,4,5], take place through horizontal drilling and hydraulic fracturing techniques. In addition, some recent studies confirm the efficacy of engineered rock fracturing for improving hard-rock cuttability in mining extraction operations [6,7].

The most commonly deployed method, hydraulic fracturing (HF), has enabled the exploitation of tight formations and unconventional reservoirs. However, its deployment is accompanied by mounting environmental and operational concerns. First, HF is resource-intensive, requiring 4–6.6 million gallons (15–25 million liters) of water per shale well, which places pressure on already strained freshwater systems, particularly in arid regions [6]. Second, HF operations might cause measurable seismicity (magnitude: ~1–2.0) in 5–10% of projects [7,8,9]. This is because they change the pore pressure and activate faults. The carbon footprint of HF is also increased by the movement and injection of proppants, which account for 8–12% of all emissions in a normal well’s lifecycle [10,11,12]. Because of these concerns, along with problems like formation damage, chemical leakage, and not being able to control how fractures propagate, we need new technology to develop subsurface resources in the future.

One promising alternative is electrohydraulic fracturing (EHF) technology, which uses high-voltage electrical pulses to induce stress and fracture initiation within rock formations [13]. The application of high-voltage discharge for the purpose of enhancing oil shale production was announced in 1964 [14]. The electric supply entails accumulating and releasing energy from capacitors to electrodes positioned in a wellbore, which triggers powerful plasma and intense shockwaves capable of fracturing the reservoir, the extent of which is proportional to the discharged energy. This technique is applied in two distinct forms, including Pulsed Corona Electrohydraulic Discharge (PCED) and Pulsed Arc Electrohydraulic Discharge (PAED) [13,15].

PCED, which is also referred to as a corona discharge, operates on the concept of low-energy and high-voltage electrical pulses to produce a non-thermal plasma [13,15]. It occurs in isolated zones around the electrode tip when the electric field intensity surpasses the liquid’s dielectric breakdown threshold. The discharge produces UV light in addition to reactive chemicals. These items are very good at encouraging chemical reactions and sterilization techniques. However, PCED has no major mechanical effect as it does not produce powerful shockwaves or cavitation, which makes it unsuitable for uses needing physical disturbance, such as rock fracturing.

On the other hand, PAED is a high-energy process that produces strong electrical arcs between submerged electrodes [16]. Once the liquid’s breakdown voltage is exceeded, the arcs produce conductive plasma channels that release enormous amounts of energy. Rapid liquid evaporation, explosive bubble growth, and intense shockwaves follow, causing cavitation effects. These shockwaves and associated thermal stresses have a notable mechanical impact, hence making PAED a useful instrument for fracturing. With electrode gaps designed to endure great strains, the method usually runs with large currents of up to thousands of amperes and pulse lengths ranging in microseconds.

PAED appeared to produce scattered microcracks by applying a rapid dynamic force on rock, in contrast to the quasi-static character of HF [17]. An analysis of the shockwaves created by submerged PAED [18,19] also revealed that when the power input hits a specific critical threshold, the permeability of the rock near the impactful waves increases greatly, even if there is no visible cracking that can be observed. Nevertheless, there are cases when PAED is not as efficient as expected because of complicated subsurface circumstances like excessive thermal and fluid conductance [20]. In addition, boosting acceleration and water molecule dispersion consume a considerable amount of discharged energy. As a result, it might be challenging to achieve levels of efficacy higher than the electric current in water. Shockwaves converted less than 25% of the absorbed electrical energy towards mechanical power in recent PAED studies [21,22]. Inadequate conversion of electric to kinetic power renders PAED a non-impactful possibility in HF treatments of unconventional rocks for flow enhancement.

A novel approach called 3PS has been developed as an upgrade to traditional PAED. One unique feature of 3PS is its capacity to produce plasma that undergoes a thermite reaction [15,18]. By introducing a thin fusible link in between the two submerged electrodes, an electrochemical reaction can be initiated, resulting in augmentation of the electrical input. For this reason, aluminum (Al) is the most suitable substance to use as an initiator. The interaction between aqueous molecules and ionized Al in plasma causes an exothermic reaction, which may boost the initial energy discharge by several times [15,23]. 3PS may induce numerous microfractures linked to pre-existing fissures, leading to significant enhancement of the near-wellbore permeability in contrast to the bi-wing fractures observed in the conventional HF method [15].

2. Principles of Pulsed Power Plasma Stimulation

Rock fracturing using 3PS could lead to a technological breakthrough. The main principle of this technology relies on the application of high-voltage electrical pulses of kilovolts through electrodes inserted into a fluid-filled borehole drilled into a rock specimen. As illustrated in Figure 1, when the electrical potential exceeds the dielectric strength of the medium (commonly water or brine), a rapid electrical breakdown occurs, which results in the formation of a highly conductive plasma channel. This plasma expands almost instantaneously, generating a sharp rise in local pressure and producing strong shockwaves that radiate outward into the surrounding rock. These shockwaves induce high-intensity tensile and shear stresses that exceed the rock’s fracture strength, leading to the initiation and propagation of micro- to macro-scale fractures. With the control of the fracturing process via pulse parameter modulation, the technology can provide much lower adverse effects on the environment in comparison to existing traditional methods, such as HF and acid stimulation.

Figure 2 illustrates the key differences between 3PS and the prominent rock stimulation methods, such as HF and gas gun methods, where each method is defined by its characteristic pressure magnitude and duration of energy delivery. HF delivers pressure gradually, reaching approximately 5000 psi over a prolonged duration of up to 1 h [22]. This approach enables slow fracture propagation, typically aligned with natural bedding planes. However, it requires large volumes of water and proppants, raising concerns regarding aquifer depletion, chemical contamination, and induced seismicity. The extended stimulation period also increases thermal and pressure dissipation, limiting its efficacy in hard or low-permeability formations.

Gas gun systems, on the other hand, generate a moderate pressure pulse (~20,000 psi) over ~10 milliseconds suitable for near-wellbore fracture enhancement [24]. While they offer improved pressure intensity compared to hydraulic methods, gas guns lack sufficient penetration and repeatability, and their ability to control fracture geometry remains limited. They are more applicable for damage mitigation or stimulation in soft formations.

Meanwhile, 3PS produces a high-amplitude, ultrafast pressure pulse of up to 100,000 psi within 10 microseconds [23]. This rapid discharge is achieved through the vaporization of a fusible link (e.g., aluminum wire) within a conductive medium, forming a transient plasma arc and generating a supersonic shockwave. The high strain rate initiates complex fracture networks, even in high-strength, low-permeability rock such as granite and basalt. Unlike hydraulic methods, 3PS minimizes fluid volume, environmental footprint, and seismic risk, making it a promising alternative for geothermal, unconventional oil and gas, and mining operations.

Figure 2. Comparative pressure–time characteristics of 3PS, HF, gas gun, and explosive stimulation techniques (after Lati, 2010 [25]).

Figure 2. Comparative pressure–time characteristics of 3PS, HF, gas gun, and explosive stimulation techniques (after Lati, 2010 [25]).

2.1. Basic Principles

The basis of 3PS lies in the ability to generate high-voltage pulsed outputs using advanced energy storage devices like capacitors and inductors (Figure 3). Capacitors store energy and generate high-voltage pulses through quick discharging. On the other hand, inductors enable pulse control in terms of rise time and duration [26]. Together, these elements produce precise and effective electrical discharges. Pulsed Power (PP) technology can utilize such components to generate the requisite mechanical stresses and shockwaves that create fractures within rock, whilst reducing extraneous energy losses in the process. Consequently, 3PS provides the application of energy with a distinct utility.

Moreover, the discharge processes that serve as the basis for PP technology are vital to the creation of plasma (mainly through the use of electrohydraulic discharges). The rapid release of energy during pulsed electrical discharges results in the vaporization of material in the discharge channel, creating high-temperature plasma and high pressure, which are capable of creating mechanical stresses in the rock [27]. Therefore, the targeted application of discharge energy is important for the development of plasma channels, which allows more efficient rock fracturing processes compared to existing methods.

The plasma channels in PP applications play an important role in creating shockwaves and mechanical stress in the rock required for fracturing. The quick discharge of energy starts the plasma channel’s elongation, converting electrical energy to thermal and kinetic energy, creating mechanical stress in the rock structure. Stress waves travel within the rock and create fractures along natural fault lines [26]. This behavior is different from hydraulic fracturing, which uses fluid pressure to generate fractures in the rock. Plasma channels create electromechanical coupling and allow the application of energy into the rock as needed, improving crack control and reducing the amount of fluid necessary for conventional methods [27].

2.2. Mechanisms of Rock Fracturing

The localized vaporization of the medium present within the discharge channel leads to an increase in the internal pressure along the plasma channel, which in turn expands the pre-existing microcracks and initiates the propagation of new fissures by taking advantage of natural weaknesses, such as grain boundaries and other previous damage (Figure 4). By exploiting these weaknesses present in the rock, fracture networks are propagated with very low energy consumption compared to more traditionally used fracture methods [26,27,28]. Thus, the process of plasma propagation in rocks takes advantage of how the target rock behaves under certain conditions, optimizing the initiation and evolution of fractures, avoiding extensive fracturing of surrounding layers when it is not required, and providing benefits in terms of energy consumption and the environmental impact of the process [15,29].

Along the same line, the mechanism of rock transmutations differs between thermal fracturing and pulsed discharges. Thermal fracturing relies on extreme heat to achieve expansion and rupturing of the inner rock structure. On the other hand, pulsed discharges allow direct conversion of electric energy into mechanical work, which is achieved by electrical discharge and the establishment of a plasma channel. Such a mechanism allows for more efficient and controlled fracturing, increasing delivery efficiency and reducing energy input, exploiting the pre-existing flaws in the rock structure [27]. Additionally, it represents a significantly more eco-friendly technique, minimizing the thermal pollution and fluid use typical of thermal rock demolition [28]. In fact, this mechanism can leverage the electric delivery advantages to disturb the rock matrix in an even more efficient way, yielding specific characterized reduced environmental impacts.

2.3. Key Parameters Influencing Performance

Pulse amplitude is one of the key parameters that influence the efficiency of rock fracturing with the application of PP technologies. Taking into consideration that the energy input directly influences the rock and is able to create fractures as well as penetrate the depths of rock layers, high pulse energies improve all of the aforementioned characteristics [15,26]. With the increase in the discharged voltage, the propagation area of the plasma channel within the target rock also expands, thus allowing the creation of new fractures while widening the existing fractures [30]. Given that the fractures in rocks depend on mentioned technological factors and that their efficiency is characterized by a relationship between amplifying the pulse amplitude and certain rock properties, such as tensile strength, porosity, etc., their correlation should evidently be applied. In this regard, precise pulse amplitude control provides an opportunity to target rock characteristics in a specific manner, thus improving fracturing in a particular area and preserving energy in other regions to achieve fracturing efficiency while at the same time being environmentally responsible.

Pulse frequency and duration are also critical specifications impacting PP technology’s rock fracture performance. The pulse frequency indicates the pulse–stress application’s periodicity, as an optimal frequency ensures that the pulse cycle when applied fractures the rock [30]. Lower frequencies may promote rock stress energy absorption, resulting in significant and controllable fractures. Conversely, applying high-frequency pulses produces rapid impacts that encourage rock disaggregation. Pulse duration indicates the energy application’s time length, as it affects the energy contained in each pulse over time. A combination of pulse frequency and duration influences the fracture efficiency that fits different rock types and stress conditions, improving efficiency and minimizing the unnecessary energy loss from rock deformation [30].

Moreover, it is imperative to consider that the waveform parameters of PP significantly influence the efficiency and accuracy of rock fracturing. The waveform shape and its stability affect the channel formation distribution and strength of the plasma, determining the fracture size and its impact on rock. Square-wave, high-voltage pulses with a constant amplitude across the pulse duration allow the plasma channels to propagate stably and contribute to rock fracturing [31]. On the other hand, other waveform shapes, such as sinusoidal or triangular waveforms, also present a constant amplitude but are non-stable in the time domain. Their use can lead to disruptive energy transmission changes, instability of power delivery, uneven energy imparting, and, as a result, inefficient use. Such dependence between energy propagation and the waveform instruments of rock fracturing should be considered when creating a perfect waveform. This would facilitate employing the maximum energy input into the cracking effect and avoid wasting energy through consumption in other unstable channels.

It is also worth noting that tensile strength and porosity are among the intrinsic properties of rock formations that have a bearing on the efficacy of PP in producing sufficiently efficient fractures. As a lower tensile strength means a rock formation can develop fractures upon pulsed discharge application, rock formations whose tensile strength behavior is more brittle are more likely to be damaged than less brittle ones [15]. By the same token, porosity determines the spread and absorption of released energies. Higher porosity leads to increased crack spread, and this characteristic can, along with rock properties and PP parameters, explain why some particular formations need to be supplied with energy to optimize fracture results. These aspects make it necessary to inspect rock mechanical properties so that PP parameters can be configured with characteristics that can work with those of the geological parameters to conserve the energy extracted from resource operations while enhancing leakage and extraction in processes [28].

Additionally, in situ stress conditions and the mineralogy of rocks play a pivotal role in the effectiveness of 3PS in fracturing rocks. The in situ stress anisotropy or heterogeneity determines the propagation and orientation of fractures in a particular direction, and more discharged energy is required to fracture rock at higher confining stresses [26]. In addition, the in situ stresses generally influence the effectiveness of the energy transmission as well, consequently influencing the fracture density and length. The mineralogical differences also influence the mechanical properties of the rocks and, more importantly, the propagation nature of the plasma channel within the rocks and the triggering mechanism to create fractures. Heterogeneous rocks may experience more fractures due to the differential mechanical responses of different constituent minerals due to mechanical stress imparted by the pulsed discharges [15]. Overall, knowledge of these geological parameters is significant in adjusting the PP parameters to enhance fracture networks for the achievement of environmentally friendly energy extraction.

In addition, electrode geometry and arrangement are significant factors that affect the effectiveness of PP systems. The electrode geometry has a direct impact on the sparsity and strength of the electric field, determining how plasma channels propagate through the surrounding rock [25]. Some specific designs, like pointed or spherical electrodes, can considerably increase the discharge concentration, resulting in more effective energy concentrations capable of being transmitted to specific locations within the rock mass, further assisting fracture initiation. The electrodes’ arrangement, including the distance between them and their orientation, also influences the discharge path, affecting the fracture density and extension created by the subsequent plasma channels [27]. The use of fusible aluminum wires with different thicknesses and lengths resulted in more significant rock damage with longer and wider fractures due to the extra energy released from the thermite reaction with water compared with unused aluminum wire [15]. Therefore, careful design and precise positioning of the electrodes and fusible links are crucial to further enhance the PP systems’ efficiency, consistent with a sustainable energy approach (Figure 5).

Lastly, the use of coupling media also plays a significant role in the effectiveness of PP technologies in transmitting energy during a rock fracturing operation. Coupling media generally consist of fluids such as water or gel that conduct electric energy into the target rock structure. These media enable efficient and consistent propagation of plasma channels by allowing a uniform contact between the electrodes and the rock formation. The coupling media help in the conditional transport of high-voltage pulses into the target material, which is critical for the successful character formation in the specimen. However, design challenges exist in the downhole usage of coupling fluids considering the operational constraints over the applicable coupling media and the downhole dynamical and thermal effect on the system. These design hardships occur due to the limited applicable coupling materials and the extreme geological working conditions for pulse operation and necessitate the use of more reliable system designs [27]. However, the design coupling systems demand an adequate balance regarding the aspects of ensuring reliable operation, integrating the coupling fluid benefits, and ensuring the native rock response.

3. Comprehensive Review

This comprehensive review chronologically examines the evolution of pulse plasma-based fracturing technology in reservoir stimulation from the 1960s to 2024. The review synthesizes findings from research papers spanning six decades of development, covering fundamental principles, experimental methodologies, technological innovations, and field applications (Appendix A). By analyzing early foundational studies through recent advanced implementations, this article tracks the progression of pulse plasma techniques from basic electrical fracturing concepts to sophisticated 3PS systems. The review highlights key technological milestones, fracturing mechanisms, influential parameters, material responses, and current limitations while identifying promising research directions. This systematic chronological assessment provides valuable insights into plasma-based stimulation’s potential as an environmentally conscious alternative to conventional well stimulation for enhancing reservoir productivity.

3.1. Introduction and Historical Development

3.1.1. Early Developments (1960s–1970s)

The concept of using electrical energy for rock fracturing dates back to the late 1960s, when Melton and Cross [14] conducted pioneering research on fracturing oil shale with electricity. Their study represented one of the earliest attempts to explore the feasibility of using high-voltage electricity as an alternative to conventional fracturing methods. Through laboratory experiments and field tests, they investigated the breakdown voltage required for fracturing shale, the effectiveness across varying electrode spacings, and the impact under different overburden stresses. Their findings demonstrated that electrical fracturing could successfully create horizontal fractures and improve near-wellbore permeability. Moreover, they discovered that hybrid approaches combining electrical fracturing with conventional techniques (such as explosives) further enhanced permeability around wellbores. This methodology offered a scalable and precise approach for improving oil recovery efficiency while potentially minimizing environmental impacts. However, they noted limitations, including variations in effectiveness across different grades of oil shale and challenges in controlling energy levels to avoid electrode damage. Their work highlighted the need for improved voltage control and broader testing across diverse geological settings.

Building on these early efforts, Shugar and Odello [32] investigated the use of electrohydraulic pulsers to generate stress waves for fracturing brittle materials, with potential applications for improved tunneling techniques. Their research focused on whether electrohydraulic blasts could create controlled fractures in hydrostone specimens. Through two experimental phases, they tested hydrostone cylinders with a modified electrohydraulic system, examining fracture patterns, energy transfer efficiency, and overall system performance. Their results demonstrated the successful creation of radial fractures, though achieving the desired circumferential spall patterns proved challenging. The researchers made several technical improvements, such as reducing cable resistance to increase energy delivery, but encountered issues, including long spark durations and misaligned stress pulses, that hindered ideal fracture results. Their work emphasized the need to optimize pulse settings and test various materials to advance this technique’s potential for rock excavation.

3.1.2. Technological Advancement (1980s–1990s)

The late 1980s saw continued development, with Touryan et al. [33] addressing challenges in efficiently fracturing brittle rocks for applications like drilling and rock excavation. Their research focused on evaluating the feasibility of using electrohydraulic PP-generated shocks with an 80 kJ PP facility to fracture rocks such as Berea sandstone and Lueders limestone. Their methodology involved experimental tests with various electrode designs and configurations, along with detailed measurements of pressure, energy transfer, and fracture patterns. Their findings showed that electrohydraulic pulses successfully induced fractures, achieving erosion rates of up to 0.25 cm/s and penetration rates of 7–10 m/h. These results demonstrated the potential for high-efficiency rock disintegration, with applications in mining and drilling. However, they identified limitations such as inefficient energy transfer, challenges in controlling pulse characteristics, and the need for broader material testing. Their research highlighted gaps in optimizing shockwave geometry and scaling the technology for field applications.

3.2. Fundamental Mechanisms and Physics (2000s–Early 2010s)

3.2.1. Plasma Generation and Characterization

Research in the early 2000s focused increasingly on understanding the fundamental physics behind plasma generation for fracturing applications. Grinenko et al. [34] investigated the generation of strongly coupled plasma during underwater electrical wire explosion (UEWE), a phenomenon with applications in plasma physics and potentially in reservoir stimulation. Their study analyzed plasma channel parameters, including temperature, density, and pressure distributions. Using a combination of experimental methods and numerical simulations based on a 1D magnetohydrodynamic model, they characterized plasma behavior under extreme conditions. Their findings showed good agreement between experimental and numerical results, validating the semi-empirical conductivity model they employed. However, they identified challenges related to a nonuniform spatial distribution of plasma parameters and limitations in temperature estimation during early discharge stages.

Veksler et al. [35] expanded this work by investigating shockwave generation through UEWE, with a focus on maximizing shockwave pressure and improving energy transfer efficiency. They examined the optimization of wire configurations, confinement techniques, and generator parameters. Using experimental setups with microsecond and submicrosecond timescales, they evaluated straight and zigzag wire designs, as well as the impact of shockwave confinement using Perspex plates. Their key findings included achieving higher shockwave pressures with zigzag configurations and confined setups, demonstrating energy transfer efficiencies of up to 85%, and identifying enhanced heating rates in thinner wire segments. However, they noted limitations such as the reduced electrical performance of zigzag wires, rapid pressure dissipation, and complexities in confinement-induced interference.

3.2.2. Application to Permeability Enhancement

The practical application of plasma technology for enhancing material permeability gained significant attention around 2010. Maurel et al. [36] investigated the use of PAED to enhance the intrinsic permeability of mortar, with potential applications in oil and gas reservoir stimulation as an alternative to hydraulic fracturing. They examined the correlation between dynamic shockwave-induced damage and permeability evolution in cementitious materials. Their methodology involved generating compressive shockwaves in water with pressures reaching 250 MPa and applying single and repeated shocks to mortar specimens. The researchers found a permeability threshold, above which permeability increased linearly with applied pressure, and demonstrated that repeated shocks amplified this effect. Their findings suggested that PAED-induced diffuse microcracking could significantly increase permeability without causing excessive macrocracking, making it promising for enhancing gas production in tight reservoirs.

Chen et al. [37] continued this line of research, investigating PAED technology for generating shockwaves in water as an alternative to conventional hydraulic fracturing for enhancing rock permeability in tight gas reservoirs. Their objective was to explore how shockwaves could create distributed networks of microcracks in rocks, improving permeability while minimizing environmental impact. Using experimental setups to measure shockwave propagation and pressure profiles, complemented by numerical simulations, they demonstrated that PAED-generated shockwaves significantly increased rock permeability through dynamic microcracking, with linear permeability growth observed beyond a certain energy threshold. However, they noted challenges in measuring high-frequency shockwaves and ensuring consistent energy distribution. They identified gaps in the understanding of the precise mechanisms of shockwave interaction with rock structures and suggested further research to optimize energy transfer and refine numerical models.

3.3. Technical Optimization and Parameter Studies (Mid-2010s)

3.3.1. Discharge Optimization Studies

By the mid-2010s, researchers were focusing on optimizing discharge parameters for more effective fracturing. Carden [38] analyzed EHSG from an energy conversion perspective, examining the relationship between electrical, thermal, and physical parameters. The methodology involved experimental analysis of key variables such as electrode gap distance and charge voltage, using transient RLC circuit models and various measurements. The findings confirmed a linear relationship between charge voltage and peak pressure, with optimized electrode gaps producing maximum pressures of up to 900 psi. However, variability in arc location and electrode damage were identified as significant limitations, emphasizing the need for durable electrode designs and consistent arc control.

Zhu et al. [39] investigated the influence of water conductivity on PAED, focusing on improving efficiency for applications like water treatment. They analyzed how varying conductivity affected discharge behavior, sterilization effectiveness, and energy transfer. Their findings indicated that higher conductivity reduced breakdown voltage, discharge current, and pressure wave intensity, while also shortening pre-breakdown delay time. However, excessive conductivity could shift the discharge mode from PAED to PCED, limiting sterilization efficiency. The research highlighted the need for optimizing water conductivity and discharge settings to maximize PAED’s potential for various applications.

3.3.2. Material Selection and Configuration

Zhou et al. [40] explored how plasma-ignited energetic materials could enhance electrohydraulic shockwaves for applications like shale gas extraction and mining. Their research focused on how factors like wire configuration, material type, and charging voltage influenced energetic material ignition and shockwave performance. Testing copper and molybdenum wires of varying diameters under different energy levels, they found that higher charging voltages significantly improved ignition efficiency and shockwave strength, with copper wires outperforming molybdenum due to better energy transfer and higher plasma temperatures. However, challenges remained related to incomplete wire vaporization and variability in arc plasma behavior.

Cho et al. [41] examined the application of high-voltage pulse discharge technology for rock fragmentation, focusing on understanding the relationship between rocks’ dielectric breakdown properties and fracture patterns. Testing seven different types of rocks and a cement paste, they correlated physical and mechanical properties with dielectric breakdown strength. The results showed that denser rocks with higher mechanical strength exhibited greater dielectric breakdown resistance, and fractures often followed mineral component boundaries. However, they noted inconsistencies in voltage pulse timings and disparities between simulations and real-world data.

Han et al. [42] explored UEWE using three different discharge types (Type-A, Type-B, and Type-C) to better understand energy deposition and shockwave generation. Using copper and tungsten wires with a 500 J pulsed current source, they found significant differences across discharge types, with Type-C achieving optimal energy deposition and peak pressures exceeding 7.5 MPa. However, they noted challenges in maintaining consistent arc behavior and achieving optimal discharge conditions.

3.4. Application Development and Practical Implementation (2017–2020)

3.4.1. Fracturing Applications

Liu et al. [43] explored the fracturing effects of electrohydraulic shockwaves generated by plasma-ignited energetic materials, addressing the challenge of enhancing unconventional gas extraction while mitigating environmental risks. They found that these shockwaves created networks of cell-shaped and penetration cracks, significantly reducing fracture pressure by approximately 54.5% compared to traditional methods. This demonstrated the potential of electrohydraulic shockwaves as a promising alternative for well stimulation, offering environmental benefits such as reduced water usage and waste generation.

Han et al. [44] conducted a comprehensive comparison study of electrical explosions of various metal wires (Al, Ti, Fe, Ni, Cu, Nb, Mo, Ag, Ta, W, W-Re, Pt, and Au) in water under consistent experimental conditions. They examined the correlation between material properties and resulting shockwave strengths, optical emissions, and energy deposition. Their findings revealed that non-refractory metals (e.g., Al and Cu) absorbed more energy than needed for atomization and generated stronger shockwaves but weaker light emissions, while refractory metals (e.g., W and Ta) produced weaker shockwaves but intense optical radiation. This comprehensive comparison aided in selecting appropriate materials for applications requiring controlled shockwave or plasma generation.

Liu et al. [45] introduced an enhanced oil recovery technique based on repetitive electrohydraulic shockwaves, offering an environmentally friendly and cost-effective alternative to traditional hydraulic fracturing. The shockwaves, produced by rapid plasma channel expansion during liquid pulsed discharges, created microcracks that enhanced rock permeability. Field trials in low-permeability reservoirs in Karamay, China, demonstrated nearly doubled oil production in treated wells. However, the technique was limited in range to only a few meters from the borehole, requiring further optimization for widespread application.

3.4.2. Technical Reviews and Comparative Studies

Zhang et al. [46] provided a comprehensive review of emerging waterless fracturing technologies as sustainable alternatives to conventional hydraulic fracturing. They categorized and evaluated multiple non-aqueous fracturing fluids based on mechanisms, operational strengths, limitations, environmental impact, and economic feasibility. Economic analyses revealed that while waterless technologies had higher upfront costs, they offered lower environmental and water management expenses long-term. Supercritical CO₂ and Liquified Petroleum Gas showed promise in shale stimulation due to superior microfracture generation and recyclability.

Tariq et al. [47] reviewed pulse fracturing (also known as high-energy gas fracturing or dynamic fracturing) as an effective stimulation technique for unconventional reservoirs. Unlike conventional hydraulic fracturing, pulse fracturing uses rapid pressurization via chemical, mechanical, or gas-based means to initiate multiple radial fractures without pressurized liquid injection or proppants. They highlighted different variants of pulse fracturing and compared them based on fracture morphology, stress wave mechanics, and operational feasibility. Pulse fracturing was noted as particularly advantageous in scenarios with limited water access or naturally fractured reservoirs, though limitations included the inability to transport proppants and short fracture lengths.

3.5. Recent Advances and Specialized Applications (2019–2024)

3.5.1. Laboratory-Scale Testing and Characterization

Riu et al. [48] investigated the feasibility of plasma blasting as a water-efficient, chemically clean alternative to hydraulic fracturing. Laboratory-scale tests on cement mortar and sandstone specimens under triaxial stress conditions showed that discharge energy, controlled via gap distances and reaching up to ~17 kJ, initiated fractures influenced by differential stress magnitudes. At low stress differences, multiple, variably oriented fractures formed, while higher stress differences yielded fewer but longer fractures aligned with the minor principal stress. Multi-stage blasting extended existing fractures without causing borehole collapse, a key safety advantage over explosive methods.

Li et al. [49] investigated rock behavior under harmonic excitation, focusing on resonance characteristics relevant to Resonance Enhanced Drilling. They proposed theoretical models to calculate rock’s natural frequency based on mechanical and geometric properties and used finite element simulations to evaluate resonance frequency responses under varying conditions. Laboratory ultrasonic tests validated their models, showing that resonance frequency increases with excitation frequency, decreases with mass/volume, and is strongly affected by shape and stiffness.

At the University of Houston, laboratory-scale testing of 3PS has been actively conducted since 2019 using a dedicated experimental platform housed in the stimulation laboratory. The system includes a custom-designed true triaxial loading cell capable of independently applying three principal vertical, maximum horizontal, and minimum horizontal stresses of up to 3000 psi on cubic rock specimens measuring 14 inches per side (Figure 6b). A 2-inch borehole, drilled at the center of the cube, is filled with tap water to serve as the dielectric medium for plasma generation.

A high-voltage capacitor bank capable of delivering up to 20 kJ of electrical energy (Figure 6a) is discharged through a coiled aluminum wire positioned between two copper electrodes. Upon reaching the breakdown voltage, the aluminum wire vaporizes, forming a plasma channel and producing intense shockwaves and mechanical stresses that propagate into the rock, initiating fractures. As shown in Figure 6, the system accommodates full confinement during stimulation and includes provisions for safe high-voltage operation.

Hydraulic actuators integrated into the true triaxial cell (Figure 6b) control confining stresses in all directions. The electrodes are inserted through sealed feedthroughs and submerged in the water-filled borehole to ensure stable arc propagation. Figure 6c illustrates the electrode and wire configuration placed within the borehole. The discharge system is safely operated through a remote-control interface and dual-button firing system, shown in Figure 7c, which includes interlock protections and adjustable voltage settings.

Signal acquisition is managed using high-speed digital oscilloscopes (Figure 7b), which capture voltage, current, and pressure waveforms in real time. These diagnostic tools provide insights into energy delivery efficiency, plasma arc behavior, and dynamic fracture response. Meanwhile, the confining stress is continuously monitored and adjusted via a hydraulic control panel and pump system (Figure 7a), allowing realistic simulation of in situ subsurface conditions.

In addition to varying stress conditions and discharge energies on various rock types, the experimental protocols have also involved systematic testing of fusible aluminum wires with different diameters of 20–24 gauge (1.29–0.254 mm²) and lengths (20–50 cm) to optimize energy deposition and plasma stability. These parameters were found to significantly influence the initiation behavior of plasma channels and the intensity of shockwave propagation, enabling tailored stimulation designs for different rock types and field conditions.

3.5.2. Comparative Studies on Discharge Methods

Liu et al. [50] compared shockwave characteristics between Subsonic Streamer Breakdown Discharge and metal wire explosion in water under identical voltage conditions. Using high-speed photography, pressure probes, and synchronized diagnostics, they found that metal wire explosion led to significantly higher peak shockwave pressures (4.2 MPa vs. 2.4 MPa) and greater energy conversion efficiency (17.5% vs. 9.4%). They attributed this to more focused and rapid energy deposition during the plasma channel acceleration phase, whereas Subsonic Streamer Breakdown Discharge showed diffuse energy distribution with significant loss during the pre-breakdown stage.

Li et al. [51] investigated how capacitor size and current rise rate affected energy deposition and shockwave characteristics during UEWE. Using capacitors of 1 µF and 200 µF charged to the same energy levels, they found that smaller capacitors with a higher voltage yielded faster current increase rates, enhancing deposition power and improving shockwave strength. Thinner wires benefited more from a fast-rising current, whereas thicker wires suffered from energy loss due to high circuit resistance.

3.5.3. Recent Advanced Applications (2020–2024)

Recent years have seen more sophisticated applications and specialized studies of plasma-based fracturing. Bao et al. [52] proposed a constitutive damage model for coal rock under the combined action of hydrostatic pressure and high-voltage electrical pulse shockwaves, aiming to enhance coalbed methane recovery from low-permeability seams. Using a coupled electrohydraulic fracturing system, they applied controlled voltage and hydrostatic pressure to coal cores. Their novel damage variable based on effective bearing area and stress showed excellent agreement between experimental and numerical results, demonstrating that voltage had a stronger influence on damage than pressure.

Li et al. [53] investigated the effects of drilling number and distribution on fracture using pulse plasma in tight sand reservoirs. They prepared five cubic sandstone samples with two vertical open holes arranged at various angles and applied a consistent 9 kV discharge voltage through electrodes submerged in a water-based liquid medium. Their results showed that wellhead angles of 30° and 60° promoted more penetrating fractures, while 45° configurations yielded the highest fracture numbers. Simulations confirmed that more wells and reduced spacing enhanced fracture connectivity and coverage.

Xiao et al. [54] studied the electromagnetic field distribution during 3PS through laboratory experiments, analytical calculations, and numerical modeling. Experiments on concrete cylinders with a central borehole showed that water’s high permittivity enhanced electromagnetic signal penetration. Their simulations revealed that surrounding conductivity and permittivity significantly influenced signal strength and depth, validating 3PS’s potential for underground imaging.

Zhang et al. [55] experimentally investigated high-voltage electrical pulse fracturing in natural Binzhou blue granite with varying capacitances to control discharge energy. They found that a higher capacitance increased the peak current, strain, and shockwave vibration intensity, though the rate of increase diminished at higher capacitance levels. Strain and vibration signals confirmed both elastic and ductile deformation, with crack formation initiating around 3 ms post-discharge.

Yin et al. [56] investigated the application of high-voltage electric pulse technology for inducing pre-damage in hot dry rock using heated granite flake specimens. Subjecting granite samples to HVEP discharges with varying peak voltages and heating temperatures, they found that through-fracture failure initiated above 96 kV, with higher voltages producing denser microcrack networks. Electrical breakdown became easier as temperature increased, with maximum damage observed between 300 and 400 °C.

Peng et al. [57] examined the effects of plasma channel spacing on the fracture behavior of red sandstone under high-voltage pulse discharge. They subjected sandstone samples to two HVPD events at varying plasma channel spacings and found that at spacings ≤ 46 mm, fractures from successive discharges coalesced, while at larger spacings, independent fracture zones formed. Simulations confirmed that stress wave amplitude decayed exponentially with distance, and smaller plasma channel spacing facilitated tensile stress accumulation and horizontal fracture linkage.

Maddirala et al. [17] evaluated the effects of pulse plasma-based shockwave technology on sandstone porosity and pore connectivity, as shown in Figure 8. Using Indian field sandstone and Berea sandstone samples subjected to varying numbers of PPBSW pulses under confining pressure, they found that increasing pulse exposure decreased P-wave velocities, increased damage factors, and enhanced porosity and pore connectivity. In Berea sandstone, mean pore size and volume grew with more pulses, while pore frequency decreased due to pore merging.

Khalaf et al. [58] conducted experimental studies on pulsed plasma stimulation and matched them with simulation work. Testing sandstone and limestone samples under both unconfined and confined stress conditions, they found that confined samples required more plasma pulses and higher energy to initiate and extend fractures. Their simulations showed that natural fractures could arrest but also promote new fracture development, and longer-duration pressure pulses were more effective than higher peak pressures for initiating fractures.

Soliman et al. [15] explored plasma stimulation-induced fracturing across multiple materials. They found that aluminum wires produced more extensive fractures due to additional thermite reaction energy. Rock type and heterogeneity strongly influenced fracture patterns, with limestone forming multiple fractures and sandstone developing planar fractures. Under confining stress, higher energies and repetitive discharges were needed, and permeability measurements indicated up to 10–100-fold improvements in sandstone.

Awad et al. [59] optimized energy design for underwater electrical shockwave fracturing by developing a correlation between minimum discharge energy and aluminum wire parameters. Using a setup with coaxial capacitors and a high-voltage system, they established that sufficient energy to completely burn the wire ensured efficient current waveform rise and shockwave generation. Different materials responded differently, with cement fracturing with minor cracks while limestone exhibited more extensive fracturing due to its heterogeneity.

3.6. Field-Scale Applications and Case Studies

3.6.1. Early Field Applications

While many studies have focused on laboratory-scale experiments, several researchers have reported field applications of plasma-based fracturing technology. Melton and Cross [14] included field tests in their early work on fracturing oil shale with electricity, demonstrating the potential for field-scale implementation. However, detailed field results from this era are limited.

3.6.2. Recent Field Tests and Case Studies

More recent studies have provided insights into field applications. Rezaei et al. [27] investigated the effects of 3PS discharge on permeability changes around the wellbore in various rock types. Their single discharge tests without confining stress and repetitive discharge tests under tri-axial confining stress showed that fracture initiation depended on both rock type and energy level.

CT scans (Figure 9) revealed a complex network of internal fractures characterized by both planar and branching geometries indicative of mixed-mode tensile and shear fracturing. Despite the absence of visible surface cracks on the outer surfaces of the large rock cube, internal slices revealed fracture propagation along multiple orientations. The transverse CT slice (Figure 9b) notably highlighted fracture widths ranging from approximately 0.05 mm to 0.20 mm, confirming that microcracks were initiated and expanded due to 3PS. Detailed cross-sectional views in Figure 9c,d further distinguish between shear fractures appearing as clean, linear features (blue arrows) and tensile fractures, which display oblique or stepped paths with irregular geometries (green arrows). These observations demonstrate that 3PS can effectively enhance rock permeability by generating multi-scale internal fractures, even in the absence of macroscopic failure at the surface.

In a related study, Rezaei et al. [60] examined pulse plasma stimulation-induced rock damage under varying confining stresses using cubic samples of sandstone, limestone, and Austin chalk. They found that using a fusible link produced more significant fractures due to additional thermite reaction energy. Rock type strongly influenced fracture morphology, with homogeneous sandstone forming planar fractures and heterogeneous limestone developing multidirectional shear fractures. Increasing confining stress raised the energy threshold for fracturing, and repeated discharges widened and extended existing fractures.

Liu et al. [45] reported field trials of their repetitive electrohydraulic shockwave technique in low-permeability reservoirs in Karamay, China. These trials demonstrated nearly doubled oil production in treated wells, validating the method’s effectiveness despite its limited range.

3.7. Comparative Analysis of Fracturing Technologies

Plasma Fracturing vs. Conventional Hydraulic Fracturing

Several studies have compared plasma-based fracturing with conventional hydraulic fracturing. Zhang et al. [46] reviewed multiple waterless fracturing technologies, including plasma-based methods, as alternatives to conventional hydraulic fracturing. Their economic analyses revealed that while waterless technologies had higher upfront costs, they offered lower environmental and water management expenses long-term.

Tariq et al. [47] compared pulse fracturing with conventional hydraulic fracturing, noting that pulse fracturing uses rapid pressurization to initiate multiple radial fractures without pressurized liquid injection or proppants. They highlighted pulse fracturing’s advantages in scenarios with limited water access or naturally fractured reservoirs, though limitations included an inability to transport proppants and short fracture lengths.

4. Discussion

This comprehensive review highlights the evolution and current applications of pulse plasma-based fracturing technologies, synthesizing data from research papers spanning six decades, as shown in

Table A1. Summary of electrohydraulic fracturing studies in the literature.

Authors	Fracturing Technique	Tested Sample	Test Conditions	Studied Parameters	Main Findings
Melton & Cross, 1968 [14]	High-Voltage Electrical Pulse	Oil shales	Input voltage: (1.2–20) KV Borehole: horizontal and cased hole with 1.5” dia.	Breakdown voltage, electrode spacings, and overburden stress	Electrical discharge induced horizontal fractures and increased permeability near wellbore
Shugar & Odell, 1976 [32]	Pulsed Arc Electrohydraulic Discharge	Hydrostone (Gypsum cement)	Input energy: 10.7 KJ Borehole: open hole with 2” dia.	Energy delivery, pulse duration, hole depth, and fracture pattern	Creation of radial fractures Optimizing the pulse settings would improve the potential of electrohydraulic pulses for rock excavation
Touryan et al., 1989 [33]	Pulsed Arc Electrohydraulic Discharge	Brea sandstone and Leuders limestone	Input energy: (8–10) KJ Borehole: open hole with 2” dia.	Energy delivery, pulse duration, hole depth, and fracture patterns	Measured pressure was ~1 GPa Focused electrohydraulic shocks produced measurable rock erosion rates, leading to potential scalability for drilling and fracturing
Grinenko et al., 2005 [34]	Underwater Electrical Wire Explosion	N/A	Input energy: (2.4) KJ Copper wires with 85 mm in length and 0.5 mm in diameter	Plasma channel parameters, including temperature, density, and pressure distributions	Nonuniform spatial distribution of plasma parameters
Veksler et al., 2009 [35]	Underwater Electrical Wire Explosion	N/A	Input energy: (2.4) KJ Copper wires with 0.4 mm in dia.	Wire configurations (straight and zigzag); the impact of shockwave confinement	Characterized influence of wire configurations on underwater explosion dynamics
Maurel et al., 2010 [36]	Pulsed Arc Electrohydraulic Discharge	Mortar samples (100 mm dia. × 125 mm height)	Input voltage: 40 KV (maximum)	The impact of applying single and repeated shocks with pressures of up to 250 MPa on the intrinsic permeability of tested samples	Permeability increased linearly after threshold pressure; repeated shocks improved permeability by up to two orders of magnitude
Chen et al., 2013 [37]	Pulsed Arc Electrohydraulic Discharge	Mortar samples (100 mm dia. × 125 mm height)	Input voltage: 40 KV (maximum)	Simulating the distributed networks of microcracks created by the PAED using the measured pressure profiles and shockwave dynamics	PAED-generated shockwaves significantly increased rock permeability through dynamic microcracking, with linear permeability growth observed beyond a certain energy threshold
Carden, 2012 [38]	Pulsed Arc Electrohydraulic Discharge	N/A	Input energy: (9) KJ	The impact of electrode gap distance and charge voltage on shockwave characteristics	Linear relationship between charge voltage and peak pressure, with optimized electrode gaps to produce maximum pressures of up to 900 psi
Zhu et al., 2014 [39]	Pulsed Arc Electrohydraulic Discharge	N/A	Discharge voltage: (3–5) KV	The influence of water conductivity on PAED and energy transfer	Increasing water conductivity will reduce breakdown voltage, discharge current, and pressure wave intensity. However, excessive conductivity could shift the discharge mode from PAED to PCED limiting its efficiency
Zhou et al., 2015 [40]	Pulsed Arc Electrohydraulic Discharge	N/A	Testing copper and molybdenum wires of varying diameters under different discharge voltages (14–25) KV	The impact of wire configuration, material type, and charging voltage on ignition of energetic materials and shockwave performance	Higher charging voltages significantly improve ignition efficiency and shockwave strength
Cho et al., 2015 [41]	High-Voltage Electrical Pulse and Pulsed Arc Electrohydraulic Discharge	Different granites, limestone, and sandstone	Input energy: (20–80) KJ Borehole: open hole with 0.5” dia.	Understanding the relationship between rocks’ dielectric breakdown properties and fracture patterns	Denser rocks with higher mechanical strength exhibited greater dielectric breakdown resistance, and fractures often followed mineral boundaries
Han et al., 2017 [42]	Underwater Electrical Wire Explosion	N/A	Input energy: (13) KV (500 J stored) The wire was 4cm long and had a diameter of (50–300) microns	Investigation of underwater wire explosions under three different discharge types (Type-A, Type-B, and Type-C) to better understand energy deposition and shockwave generation	Type-C leads to optimal energy deposition and peak pressures exceeding 7.5 MPa
Liu et al., 2017 [43]	Plasma-Ignited Energetic Materials	Shale samples from Sichuan, China	Discharge voltage: 25 KV (2 KJ) Borehole: open hole with 3” dia.	Testing the fracturing effects of electrohydraulic shockwaves generated by plasma-ignited energetic materials	Creation of networks of cell-shaped and penetration cracks, significantly reducing fracture pressure by approximately 54.5% compared to traditional methods
Han et al., 2018 [44]	Underwater Electrical Wire Explosion	N/A	Wires of 15 different metals/alloys (4 cm long, 100–300 µm diameter) Input energy: 500 J Discharge voltage: 12.9 KV	Studying the correlation between material properties and resulting shockwave strengths, optical emissions, and energy deposition	The non-refractory metals (e.g., Al and Cu) absorbed more energy than needed for atomization and generated stronger shockwaves but weaker light emissions, while refractory metals (e.g., W and Ta) produced weaker shockwaves but intense optical radiation
Liu et al., 2018 [45]	Pulsed Arc Electrohydraulic Discharge	Cement blocks	Discharge voltage: (25–30) KV, repetitive pulses	Optimizing electrohydraulic shockwaves for rock fracturing and validation through simulation and field tests	The repeated pulses created microcracks that enhanced rock permeability Numerical simulations confirmed that the permeability improved exponentially with stress variations induced by shockwaves Field trials in China showed oil production doubled in treated wells
Xiao et al., 2018 [18]	Pulsed Power Plasma Stimulation	Cylindrical cement blocks with different casings and perforations	Input energy: 2 KJ (20 V capacitor)	Assessing mechanical and electromagnetic effects of shockwave-induced fractures Investigating the role of thermite reactions in enhancing mechanical energy output	The exothermic thermite reaction enhanced mechanical energy output by up to two orders of magnitude Generated transient electromagnetic fields were measured and simulated, showing potential for reservoir monitoring applications
Riu et al., 2019 [48]		Cement mortar cubes (20 cm), sandstone blocks (18 cm + mortar frame)	Input energy: 2.5–17 KJ Vertical borehole (3.2 cm dia.) at the center of sample	Fracture energy thresholds, stress dependence, bedding plane effects, and fracture orientation	Higher energy leads to more fractures; higher applied stresses result in fewer but longer fractures; plasma blasting enhances permeability by 4 orders
Liu et al., 2020 [50]	Underwater Electrical Wire Explosion	Water-filled test tank with copper wires and tungsten–copper electrodes with gap of 15 mm	Discharge voltage: 20 KV With a capacity for capacitor energy up to 600 KJ	Shockwave peak pressure, rise time, plasma channel radius and velocity, energy deposition rates, and efficiency	Metal wire explosions convert 17.5% of deposited energy into shockwave energy vs. 9.4% for Subsonic Streamer Breakdown Discharge Shockwaves generated by metal wire explosion are faster, stronger, more focused
Li et al., 2020 [51]	Underwater Electrical Wire Explosion	50 mm long copper wires (0.12–0.5 mm) diameter	Input energy: 115 J, 360 J, 1400 J Discharge voltages: 1.1–53 KV, depending on capacitor size	Rise rate of current, deposition energy, deposition power, discharge mode, vaporization threshold, and circuit resistance impact	Faster rise rate improves deposition energy and thereby strength of shockwaves; thinner wires overheat more easily; circuit resistance greatly limits energy deposition in thick wires
Rezaei et al., 2020a [27]	Pulsed Power Plasma Stimulation	Cement, limestone, sandstone blocks	Input energy: 2.2–12 KJ Open hole for sandstones and limestones and cased hole for cement	Confining stress, energy levels, and repeated discharges	Fracture initiation energy increased with stress; repeated discharges enhanced permeability
Rezaei et al., 2020b [60]	Pulsed Power Plasma Stimulation	Sandstone, limestone, and Austin chalk	Input energy: 8–20 KJ	Stress and fusible link effects	Higher stress needed higher energy for failure; fusible link enhanced fractures
Bao et al., 2021 [52]	High-Voltage Electrical Pulse	Anthracite coal blocks	7–13 KV (single-pulse discharge); 1–8 MPa hydrostatic pressure	Discharge voltage, pressure, crack length/aperture, applied stresses, and stimulated area	Higher voltage resulted in greater damage; voltage has more effect than pressure
Xiao et al., 2023 [54]	Pulsed Power Plasma Stimulation	Concrete cylinder	2 KJ stored energy	Effect of surrounding media on EM signal	Water enhanced EM signal transmission, while air degraded it
Zhang et al., 2023 [55]	High-Voltage Electrical Pulse	Binzhou blue granite 30 × 30 × 50 cm	10 KV, variable capacitance (20–500 µF)	Effect of capacitance on fracture	Capacitance controlled shockwave strength; visible cracks (horizontal and vertical) appeared at high capacitance
Li et al., 2024 [53]	Pulsed Arc Electrohydraulic Discharge	Tight sandstone blocks 200 × 200 × 200 mm	Discharge voltage: 9 KV with discharged current 5 kA	Effect of wellhead angle and well spacing	Well spacing/angle influenced fracture patterns and extension
Yin et al., 2024 [56]	High-Voltage Electrical Pulse	Fine-grained granite	(80–144) KV, 50 µF capacitance	Peak voltage and thermal effect on breakdown	Temperature reduced breakdown voltage threshold; enhanced crack complexity with heating
Peng et al., 2024 [57]	High-Voltage Electrical Pulse	Red sandstone 250 × 250 × 150 mm	Discharge voltage: 70 KV	Plasma channel spacing effects	Creation of horizontal fractures; optimal spacing enhanced fracture coalescence; wider spacing reduced effectiveness
Maddirala et al., 2024 [17]	Pulsed Power Plasma Stimulation	Berea sandstone cores	~300 J per pulse (25–26 KV)	Effect of pulse number on petrophysical characteristics of the tested cores	Porosity and fracture connectivity improved with increased pulses
Khalaf et al., 2024 [58]	Pulsed Power Plasma Stimulation	Sandstone and limestone	Input energy: (6–10) KJ Borehole: open hole with 2” dia. Triaxial confinement	Effects of confining stresses and different wire dimensions	Creation of horizontal and radial fractures. Repeated pulses enhanced fracture networks, and the presence of natural fractures affected their propagation
Awad et al., 2024 [59]	Pulsed Power Plasma Stimulation	Water tank and cement/limestone rocks	Input energy: (1.5–9) KJ Borehole: open hole with 2” dia.	Optimizing energy design for underwater electrical shockwave fracturing by developing a correlation between minimum discharge energy and aluminum wire parameters	A correlation was developed to determine the minimum energy required to burn the wire based on wire diameter and weight. Limestone exhibited more extensive fracturing, compared to cement, due to its heterogeneity
Soliman et al., 2024 [15]	Pulsed Power Plasma Stimulation	Cement, sandstone, limestone, and shale samples	Input energy: (6.4–20) KJ Borehole: open hole with 2” dia. Triaxial confinement	Effects of applied confining stresses, rock type, and energy input	Higher applied stresses required more energy; creation of horizontal and radial fractures; repeated discharges enhanced fractures

. Beginning in the 1960s, foundational studies by Melton and Cross [14] introduced the concept of electrically induced fracturing in oil shale, demonstrating the ability to generate horizontal fractures and improve near-wellbore permeability. Subsequent work in the 1970s carried out by Shugar and Odello [32] focused on electrohydraulic pulsers for brittle material fracturing, revealing the potential of stress wave propagation despite technical limitations in spall pattern formation. The 1980s and 1990s saw notable advancements, with Touryan et al. [33] employing an 80 kJ PP facility to fracture Berea sandstone and Leuders limestone, identifying key parameters influencing erosion and penetration rates but also emphasizing inefficiencies in energy transfer.

By the 2000s, the focus shifted toward understanding plasma generation physics. Grinenko et al. [34] and Veksler et al. [35] explored UEWEs and their shockwave characteristics, demonstrating improved energy efficiencies and validating numerical plasma models. In parallel, researchers such as Maurel et al. [36] and Chen et al. [37] began investigating the use of PAED for enhancing permeability in mortar and tight gas reservoirs. Their studies highlighted that shock-induced microcracking could significantly increase permeability without excessive macrofracture development. From the mid-2010s, optimization efforts intensified. Studies by Carden [38], Zhu et al. [39], and Zhou et al. [40] investigated discharge parameter tuning, wire material effects, and water conductivity on shockwave efficiency. Cho et al. [41] and Han et al. [42] provided insights into dielectric breakdown strength and arc behavior in various rock types, while Liu et al. [43], Han et al. [44], and Liu et al. [45] applied these principles to enhance unconventional gas production, with field results showing nearly doubled oil output despite the short stimulation radius.

Recent work from 2019 to 2024 has expanded the application base and characterization of plasma fracturing. Researchers such as Bao et al. [52], Li et al. [53], Xiao et al. [54], and Yin et al. [56] explored fracture propagation under different geometries, electric field distributions, and high-temperature conditions. Comparative studies showed that metal wire explosions produced stronger shockwaves than streamer breakdown, and capacitor sizing significantly influenced energy deposition and fracture patterns. Maddirala et al. [17] and Khalaf et al. [58] examined porosity evolution and energy scaling in sandstone and limestone samples, linking plasma exposure with increased pore connectivity and fracture coalescence. Lab tests by Rezaei et al. [27,60] and Liu et al. [45] confirmed the relevance of rock heterogeneity, confining stress, and discharge repetition in fracture development and productivity gains.

3PS is changing how geothermal energy is extracted by allowing specific and precise fracturing of challenging crystalline rocks. Unlike traditional methods that use mechanical or hydraulic stimulation, the technique utilizes high-voltage, ultrafast electric discharges to create shockwaves and localized plasma which start fractures along pre-existing weaknesses in a rock matrix. This is particularly useful in EGSs, where low-porosity lithologies require increased permeability. In crystalline formations such as basalt and granite, which are often insensitive to conventional stimulation methods, 3PS has been demonstrated to produce dense and interconnected fracture networks. These networks are essential for efficient heat transfer and fluid circulation in EGS environments. 3PS offers advantages over hydraulic fracturing, which is more detrimental to the environment, and it also utilizes less fluid and presents a reduced seismic risk [47]. Recent laboratory experiments have shown that 3PS can enhance thermal conductivity and heat extraction efficiency by increasing the fracture density of granite by 40–60% [61]. The ability to generate extremely short bursts of high pressure by pulsed plasma within microseconds is the integral impact of enhancement. These bursts create fracture environments with high strain rates, which exploit weaknesses at the grain boundaries without causing excessive stress to the surrounding formation [47,61].

Translation of these lab-scale discoveries into field-deployable technologies is making significant strides. Fraunhofer IEG and ETH Zurich developed the Plasma Pulse Geo Drilling (PPGD) method by applying 200 kV electrical discharges to fracture rock in place without making physical contact. By simulating deep geothermal environments with a Marx generator setup, laboratory tests under simulated in situ conditions (150 MPa pressure, 150 °C temperature) validated the efficacy of PPGD in granite [62,63,64]. The results demonstrated far faster penetration rates, less tool wear, and less tripping time as compared to the traditional rotary drilling methods. Parallel efforts have also explored coiled-tubing-compatible plasma systems aimed at improving mechanical penetration rates in hard rocks. In simulated modeling of Finland’s deep geothermal well, field-scale demonstrations showed a 20% increase in the rate of penetration, with a plasma bit outperforming roller cone bits. Due to the non-contact mechanism, the system ensured a longer tool life while achieving a projected ROP of 23 feet per hour as opposed to 7.7 feet per hour [65].

In addition to standalone 3PS, recent research has advanced the concept of integrating high-voltage pulsed plasma with conventional mechanical drilling tools. A notable innovation is the High-Voltage Electric Impulse–Polycrystalline Diamond Compact (HVEI-PDC) combined bit, which synergizes the benefits of plasma-induced rock weakening with the directional control and high efficiency of PDC bits. Liu et al. [66] demonstrated that coupling electrical breakdown damage with mechanical drilling significantly improves drilling performance, particularly in hard crystalline formations such as granite. The plasma discharges create microcracks and localized weakening zones ahead of the PDC cutters, allowing for faster penetration, reduced bit wear, and lower mechanical specific energy during drilling. Their dynamic damage model showed that when electrode spacing exceeded 40 mm, the HVEI-PDC bit achieved a higher rate of penetration and reduced composite specific energy compared to conventional PDC drilling. This hybrid strategy directly complements the standalone 3PS concept by offering an integrated pathway for field-deployable plasma-assisted stimulation and drilling systems which is suitable for deep oil and gas wells, EGSs, and hard-rock reservoirs, where conventional technologies struggle.

Further supporting the essential role of 3PS, Kazi et al. [67] investigated the effects of plasma pre-cracking on mechanical drilling in granite. Their single-insert cutter experiments revealed that plasma-treated granite exhibited up to a 50% reduction in cutting and thrust forces compared to untreated samples. Detailed surface analyses showed that plasma-induced microcracks facilitated intergranular failure, leading to easier material removal and improved drilling efficiency. These results validate plasma pre-cracking as a complementary technology for reducing energy requirements, improving tool longevity, and enhancing operational sustainability.

Recent advancements have further propelled the field. GA Drilling’s plasma-bit technology has been integrated into existing automated drilling systems, demonstrating the potential for contactless plasma drilling to enhance deep geothermal energy extraction. In collaboration with the National Renewable Energy Laboratory, GA Drilling is developing a high-temperature downhole generator designed to operate at temperatures of up to 250 °C, eliminating the need for external power cables and enhancing drilling efficiency. This collaboration aims to accelerate the commercialization of the plasma-bit hybrid drilling system, providing a cost-effective solution for ultra-deep geothermal energy access [68].

Additionally, the development of the ANCHORBIT technology by GA Drilling addresses the challenge of stick–slip vibrations in drilling operations [69]. This anchoring system stabilizes the bottom hole assembly, enabling consistent drilling without stick–slip, and allows for the use of high-torque or low-RPM downhole motors. By combining this anchoring technology with plasma drilling, the system enhances drilling performance in hard-rock formations, reducing the number of trips and extending the lifespan of drill bits.

Amid these developments, the NOVAS Plasma Pulse Stimulation (PPS) system introduced by Fraser [70] represents a mature and field-deployed realization of this technology. At the core of the system is a high-voltage plasma emitter available in two configurations: a 4.02” (102 mm) outer diameter tool measuring 9.02 ft (2750 mm) and a 2.50” (64 mm) OD tool at 12.96 ft (3950 mm). Each is designed for use in vertical, deviated, and horizontal wells, with compatibility across electric wireline services up to 13,000 ft and electric coiled-tubing assemblies up to 22,200 ft [71]. However, the reliance on wireline deployment introduces logistical limitations, as each set of plasma shots requires retrieval and reinsertion of the tool to reload expendable conductors. The tools are pressure rated up to 8000 psi (55,150 kPa) and can operate at temperatures of up to 203°F (95 °C), with an increase to 140 °C under development for deployment by late 2025. Operational prerequisites include a minimum 50 ft fluid column above the tool and at least 4 SPF at 13 SPM to ensure effective propagation of pressure waves. The plasma emitter comprises a capacitor bank rated ≥6 kV and ≥50 μF, delivering short-duration, high-energy discharges (1.5–2.0 kJ per pulse) through a fine metallic conductor inserted between a refractory-metal-coated high-voltage electrode and a grounded return electrode. Upon discharge, the coil vaporizes, creating metallic plasma and a broadband shockwave of ~50–55 microseconds at frequencies of up to 18–20 kHz. These oscillations produce non-linear elastic waves that radiate through the formation, disrupting capillary trapping, opening microchannels, and enhancing permeability. The emitter’s electrodes are supported on three angularly distributed metal stands converging at a 48° apex enclosed in a dielectric-filled, cone-shaped housing. Real-time performance feedback is provided via an integrated Rogowski coil.

The surface Ground Control Unit (SCU) is a modular, trailer-mounted system that manages voltage charging, discharge initiation, safety interlocks, and conductor advancement. It logs discharge parameters and coordinates pulse frequency and energy levels based on well parameters such as reservoir geology and original oil in place (OIP). Each treatment is customized in terms of duration and pulse count based on a comprehensive pre-treatment assessment. Field trials have demonstrated the efficacy and operational flexibility of the NOVAS PPS system [72,73]. Over the past decade, NOVAS Energy has deployed this technology across key petroleum basins in Russia, the United States, China, Kazakhstan, and the Middle East, demonstrating its versatility and field effectiveness in diverse geological settings.

In USA fields, 3PS applied to wells completed in limestone, sandstone, and shale formations led to 3- to 44-times increases in oil production (Figure 10). The most dramatic improvement occurred in a shale well in southwestern Colorado, where production surged from 24 to 106 barrels per day (a 342% increase). In Creek County, Oklahoma, sandstone wells improved from 1 to 44 barrels per day—an exceptionally high productivity gain.

Meanwhile, consistent increases in oil output were observed across multiple Russian fields (Figure 11). Shkapovskoe showed an extraordinary 698% increase (2.24 to 17.88 bbls/day), Vasiloskoe rose by 538%, and even higher-capacity fields like Tajlakovskoe and Krapovonskoe registered improvements of 214% and 200%, respectively.

In addition to production uplift, 3PS has proven valuable in enhancing injectivity in waterflood operations, as shown in Russian injection wells (Figure 12). Results indicate significant improvement in water injection rates, which is critical for maintaining reservoir pressure and sweep efficiency in EOR projects. Lomovoe and Sutorminskoe saw injectivity gains of 512% and 588%, respectively. Tajlakovskoe, with its low initial injectivity (31 bbls/day), improved over 1000% to 376 bbls/day, enabling it to become a viable injector. Muravlenkovskoe, already operating at high injection rates, still experienced a 155% improvement, confirming the value of 3PS even in relatively healthy wells.

The field 3PS systems represent a frontier in subsurface stimulation, combining minimal environmental impact, scalable electrification, and broad lithologic applicability. Their ability to activate damaged, tight, or unresponsive formations without chemical additives positions plasma technologies as cutting-edge solutions in both hydrocarbon [74] and geothermal energy development.

Recent advancements are further reflected in the US Patent 10,309,202 B2 [75], which demonstrates the use of electrically generated shockwaves via plasma discharge or thermite-induced chemical reactions as a novel means of improving hydraulic fracture propagation and complexity. The approach employs a combination of primary and secondary shockwaves, applied precisely during fluid injection, to stimulate both natural fracture swarms and near-tip fracture growth in real time.

Current field-scale plasma shock stimulation technologies face significant limitations in the number of plasma discharges that can be delivered during a single deployment, primarily due to the need for frequent wire replacements after each shot cycle. This necessitates repeated tool retrieval and redeployment, reducing operational efficiency and hindering continuous high-energy stimulation across long laterals or multi-stage completions. The NOVAS PPS tool incorporates a wire delivery system consisting of a spool-fed conductor advanced by a plunger-type electromagnet through a guiding bush into the electrode gap, as can be seen in Figure 13. This system, housed in a hermetically sealed, dielectric-filled enclosure, enables rapid reloading and supports multi-pulse operation. However, under harsh downhole conditions, its performance is constrained by potential wire feed failures due to debris accumulation, misalignment, or mechanical wear—ultimately limiting the tool’s reliability and effectiveness during extended or continuous stimulation campaigns.

Moreover, the use of downhole capacitors to store and release high-voltage energy introduces both advantages and trade-offs. While the confined physical volume and thermal conditions limit capacitor size and thus cap the energy of each pulse—reducing the stimulated rock volume per discharge—the approach offers a key operational benefit: it eliminates the need for specialized high-voltage cables, thereby reducing surface power requirements and deployment complexity. This design allows the tool to be conveyed on standard wireline or slickline systems, significantly lowering the cost and expanding compatibility with conventional well service equipment. In contrast, using surface-based capacitors to generate and transmit energy downhole requires the use of high-insulation, pulse-rated electric cable, typically limited to coiled-tubing operations due to handling constraints and safety concerns. These cables are costly, rigid, and logistically challenging, particularly in high-angle or deviated wells. Thus, while downhole capacitor integration limits individual pulse strength, it enables broader field applicability and cost-effective deployment, especially in existing completion environments where coiled-tubing options are unavailable.

The shortage of established standard regulations specifically suited to 3PS technology is one of the main hurdles to its wider adoption. Due to its unique mechanism and limited field-scale implementation to date, plasma-based stimulation is still largely unregulated, whereas conventional hydraulic fracturing is governed by a well-developed framework of environmental and operational guidelines. In environmentally sensitive regions, such as areas with protected groundwater resources or seismic risk, regulatory agencies typically require detailed environmental impact assessments and proof of containment integrity. However, no formal codes or permitting pathways currently exist for non-hydraulic plasma stimulation technologies.

This lack of rules is both a challenge and an opportunity. On the one hand, operators may face delays or uncertainty when seeking project approval, especially if there are concerns about high-voltage discharge. On the other hand, 3PS has clear environmental benefits, such as less water usage, no chemical additive requirements, and taking up less space on the ground. These benefits could fit well with recent regulations that focus on sustainability. The regulatory agencies will need to conduct a lot of collaborative research and pilot projects to come up with evidence-based procedures to weigh the risks and benefits of plasma stimulation. To use 3PS safely and responsibly in both hydrocarbon and geothermal applications, it will be important to set performance-based standards, safety thresholds, and monitoring protocols.

5. Conclusions

Pulse Power Plasma Stimulation (3PS) is redefining subsurface stimulation by providing a cleaner, more targeted alternative to conventional methods. The technology employs high-voltage, ultrafast electrical discharges to generate localized plasma and shockwaves, effectively fracturing rock along its natural planes of weakness. This mechanism is particularly advantageous in tight, crystalline formations where traditional hydraulic fracturing proves inefficient. Unlike conventional techniques, 3PS enhances permeability without dependence on water, chemical additives, or far-field stress conditions, making it a highly attractive solution for both hydrocarbon recovery and Enhanced Geothermal Systems (EGSs).

Over the years, 3PS has moved from lab-scale proof-of-concept to field-ready deployment, showing impressive results across a range of geological settings—from increased oil production in low-permeability zones to dramatic improvements in water injectivity for enhanced recovery. However, like many emerging technologies, it still carries some constraints. The need to replace a fine conductor wire after each pulse, combined with limited energy storage in downhole capacitors, restricts the number and strength of discharges per run. While placing capacitors downhole simplifies operations and avoids the cost and rigidity of surface-fed, high-voltage cables, it also limits how much energy can be delivered with each pulse.

Even so, the progress is undeniable. The system’s compact design, low environmental footprint, and compatibility with existing wireline infrastructure make it adaptable and cost-effective. With continued development—particularly in extending stimulation reach, improving wire feed reliability, and automating discharge control—3PS has the potential to become not just an alternative, but a preferred method for stimulating complex, low-permeability reservoirs. The path ahead lies in refining what already works, scaling up what is promising, and continuing to align this high-potential technology with the evolving demands of cleaner, smarter energy systems.