High voltage protection and shielding in downhole tools

Abstract

The downhole tool may include a voltage multiplier within the housing. The voltage multiplier may convert input power to the downhole tool from a first voltage to a second voltage higher than the first voltage. The downhole tool may also include a plurality of shielding rings surrounding at least the voltage multiplier to reduce electric field stress within the downhole tool. Additionally, the downhole tool may include an insulator located between the shielding rings and the housing.

Description

Technical Field

[0001] The present disclosure generally relates to systems and methods for electrical protection and shielding of high voltage power supplies and nuclear or photon radiation generators in downhole tools. Background Art

[0002] This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the present technology, which will be described and / or claimed below. It is believed that this discussion helps to provide the reader with background information to promote a better understanding of various aspects of the present disclosure. Therefore, it should be understood that these statements should be read from this perspective and not as any form of admission.

[0003] The production of hydrocarbons from a wellbore drilled into a geological formation is a very complex undertaking. In many cases, decisions related to hydrocarbon exploration and production can be informed by measurements from downhole logging tools that are delivered into the wellbore. These tools can be used to infer the properties and characteristics of the geological formations surrounding the wellbore to make informed decisions. Some of these tools may include radiation generators for irradiating the wellbore with nuclear radiation and sensors for making inferences based on the wellbore's response to the radiation.

[0004] Typically, an electrically powered radiation generator, such as an X-ray generator, a gamma ray generator, or a neutron generator, can use electricity to generate radiation to facilitate determining the characteristics of a surrounding environment, such as a formation. Therefore, the radiation generator can be used in a variety of situations, such as in downhole tools or for material analysis. In order to achieve high energy radiation, a high voltage power supply can be implemented. Considering the size limitations of the downhole tool, the high voltage power supply and the radiation generator can be packaged in a relatively small housing. However, placing high voltage components (such as high voltage multiplier ladder components) close to each other and / or relative to ground may result in high electric field stress and / or electrical complexity. Protecting and shielding such electrical events can improve the effectiveness, reliability, and / or life of the high voltage power supply, radiation generator, and / or downhole tool. Summary of the invention

[0005] The following is an overview of some embodiments disclosed herein. It should be understood that these aspects are presented only to provide the reader with a brief overview of these certain embodiments, and these aspects are not intended to limit the scope of the present disclosure. In fact, the present disclosure may include multiple aspects that may not be described below.

[0006] Electrically powered downhole tools, such as nuclear radiation generators, can use electrical power to generate radiation (e.g., X-rays, gamma rays, neutrons, etc.) to facilitate determining characteristics of their surroundings. To achieve high energy radiation, a high voltage power source, such as a voltage multiplier (e.g., a Cockcroft-Walton high voltage ladder or other suitable voltage multiplier) can be implemented. However, electrical components that are operably maintained at high potentials (e.g., greater than 100 kilovolts (kV)) within the confines of the downhole tool may generate high electric fields between the electrical components and relative ground. To combat the electric fields and reduce or eliminate electrical events, such as arcing, tracking, field emissions, and / or corona effects, electrical protection and shielding can be implemented around the high voltage components of the downhole tool.

[0007] In one embodiment, the downhole tool may include a voltage multiplier within the housing. The voltage multiplier may convert input power to the downhole tool from a first voltage to a second voltage higher than the first voltage. The downhole tool may also include a plurality of shielding rings surrounding at least the voltage multiplier to reduce electric field stress within the downhole tool. Additionally, the downhole tool may include an insulator located between the shielding rings and the housing.

[0008] In another embodiment, a method may include at least partially surrounding a high voltage power supply of a downhole tool with a plurality of annular shield rings to reduce electric field stress within the diameter of the shield rings. The method may also include electrically coupling a spark gap electrode to at least two of the shield rings. The spark gap electrode may propagate an arc to ground. The method may also include wrapping the shield rings with an insulator and sealing an insulating gas within a housing of the downhole tool.

[0009] In another embodiment, a downhole tool system may include a nuclear radiation generator that emits nuclear radiation; and a high voltage power supply that converts input power from a first voltage to a second voltage and provides the second voltage to the nuclear radiation generator. The downhole tool system may also include a first group of coaxial shielding rings electrically connected to a multiplication stage of the high voltage power supply and a second group of coaxial shielding rings electrically connected to a generator stage of the nuclear radiation generator. The generator stage may generate an electric field within the nuclear radiation generator to accelerate charged particles into a target to generate nuclear radiation. The downhole tool system may also include a spark gap between adjacent pairs of the first group of shielding rings to propagate an arc in response to a voltage difference greater than a threshold between at least one adjacent pair of shielding rings. The downhole tool system may also include a plastic insulator surrounding the first group of coaxial shielding rings, the second group of shielding rings, or both.

[0010] Various improvements may be made to the above features relative to various aspects of the present disclosure. Other features may also be combined in these various aspects. These improvements and additional features may exist alone or in any combination. For example, the various features discussed below with respect to one or more illustrated embodiments may be combined into any of the above aspects of the present disclosure alone or in any combination. The brief overview presented above is intended to familiarize the reader with certain aspects and backgrounds of the embodiments of the present disclosure, without being limited to the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Various aspects of the present disclosure may be better understood by reading the following detailed description and referring to the accompanying drawings, in which:

[0012] Figure 1 is an example of a downhole tool system according to an embodiment;

[0013] Figure 2 is a cross-sectional view of an exemplary downhole tool for generating nuclear radiation according to an embodiment, the downhole tool including an electrical insulator;

[0014] Figure 3 is a cross-sectional view of an exemplary downhole tool for generating nuclear radiation according to an embodiment, the downhole tool including a shield ring and an insulator;

[0015] Figure 4A is a diagram of an electric field without using a shielding ring according to an embodiment;

[0016] Figure 4B is a diagram of an electric field using a shielding ring according to an embodiment;

[0017] Figure 5 is a cross-sectional view of an exemplary downhole tool for generating nuclear radiation according to an embodiment, the downhole tool including a shield ring, an insulator, and a spark gap;

[0018] Fig. 6A is a graph of the electric field without encapsulation material according to an embodiment.

[0019] Figure 6B is a graph of an electric field with a potting material according to an embodiment; and

[0020] Figure 7 is a flow chart for implementing electrical shielding within a downhole tool according to an embodiment. DETAILED DESCRIPTION

[0021] One or more specific embodiments of the present disclosure are described below. These described embodiments are examples of the currently disclosed technology. In addition, in order to provide a brief description of these embodiments, features of the actual implementation may not be described in the specification. It should be understood that in the development of any such actual implementation, such as in any engineering or design project, many implementation-specific decisions may be made to achieve the developer's specific goals, such as complying with system-related and business-related constraints, which may vary from implementation to implementation. In addition, it should be understood that such development work may be complex and time-consuming, but for ordinary technicians who benefit from this disclosure, it will be a routine task of design, manufacturing, and manufacturing.

[0022] When introducing elements of various embodiments of the present disclosure, the articles "a," "an," and "the" are intended to indicate that there are one or more elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements in addition to the listed elements. Additionally, it should be understood that references to "one embodiment" or "an embodiment" of the present disclosure are not intended to be interpreted as excluding the existence of other embodiments that also include the recited features.

[0023] The oil and gas industry includes many sub-industries such as exploration, drilling, logging, extraction, transportation, refining, retailing, etc. During the exploration and drilling process, wellbores may be drilled into the ground for the purpose of discovering, observing, or extracting resources. These resources may include oil, natural gas, water, or any other combination of underground elements.

[0024] A wellbore, sometimes called a borehole, may be a straight or curved hole drilled into the ground from which resources are discovered, observed or extracted. During and / or after the formation of a wellbore, logging may be performed. Logging may include detailed recording of the geological formations penetrated by the wellbore and is often part of resource discovery and observation.

[0025] Exploration for subsurface objects can be accomplished through a variety of methods including surface and downhole techniques. Discovery and observation of resources using downhole techniques is typically performed in a wellbore using downhole tools. These downhole tools may be part of a tool string that may be attached to a drill or other downhole device.

[0026] A particular type of downhole tool may include an electrically powered radiation generator for generating nuclear radiation (e.g., neutrons, gamma rays, x-rays, etc.) to facilitate determining characteristics of the formation (e.g., porosity and / or mineralogy). As used herein, nuclear radiation shall include radiation of nuclear particles and / or photon particles. Depending on the desired characteristics to be determined, various types of electrically powered radiation generators may be used, such as x-ray generators, gamma ray generators, or neutron generators. For example, in a downhole tool, a radiation generator may help determine the porosity of surrounding formations based at least in part on a count of radiation (e.g., the number of neutrons or gamma rays) and / or determine the mineralogy of surrounding formations based at least in part on a radiation spectrum measured by a detector (e.g., a scintillator).

[0027] However, different types of electric radiation generators can use high voltage power supplies to facilitate the generation of nuclear radiation. For example, high voltage can be used to generate an electric field to accelerate particles (e.g., ions or electrons) toward a target. When the particles strike target atoms, radiation may be generated and output from the downhole tool. The radiation can then interact with atoms in the surrounding environment (e.g., a formation) and a response is detected.

[0028] The high voltage power source may include, for example, a Cockcroft-Walton high voltage ladder or other suitable multiplier to generate such high voltages (e.g., greater than 50 kilovolts (kV), greater than 100 kV, or greater than 400 kV). However, within the confines of the downhole tool, high electric field stresses may occur between the electrical components and the relative ground. In addition, small (e.g., less than 8 inches in diameter, less than 5 inches in diameter, or less than 3 inches in diameter) downhole tools may be more susceptible to adverse electrical effects due to the close proximity of the electrical components and / or their proximity to the relative ground. As such, shielding rings and / or insulating materials may be implemented around the electrical components of the high voltage power source and / or radiation generator to reduce or eliminate arcing, tracking, field emissions, and / or corona effects within the downhole tool.

[0029] The shielding rings can help reduce the electric field stress around the electrical components of the downhole tool by, for example, minimizing the variation of the electric field within the circumference of the shielding ring. In some embodiments, spark gaps can also be implemented between adjacent shielding rings to direct the discharge away from the electrical components of the downhole tool. Additionally or alternatively, in some embodiments, the shielding rings can be potted in a non-conductive or slightly conductive (e.g., having a resistance greater than 10 -16Siemens per meter (S / m)) to further reduce electric field stress. In addition, in some embodiments, an insulator (e.g., a plastic insulator) can be implemented around the shielding ring to further insulate the high voltage from a relative ground, such as a housing of the downhole tool. It should be understood that the embodiments described herein, although shown in the context of a downhole tool having a radiation generator, can be implemented in any suitable downhole tool that employs high voltage components for electrical protection and shielding.

[0030] Considering the foregoing, Figure 1 A well logging system 10 is shown in which the systems and methods of the present disclosure may be employed. The well logging system 10 may be used to convey a downhole tool 12 through a geological formation 14 via a wellbore 16. Figure 1 In the example of FIG. 1 , the downhole tool 12 is conveyed on the cable 18 via a logging winch system (eg, vehicle) 20. Although the logging winch system 20 is Figure 1 2 is schematically shown as a mobile logging winch system carried by a truck, but the logging winch system 20 can be substantially fixed (e.g., substantially permanent or modular long-term installation). Any suitable cable 18 for logging can be used. The cable 18 can be wound or unwound on a drum 22, and an auxiliary power supply 24 can provide energy to the logging winch system 20 and / or the downhole tool 12.

[0031] In addition, although the downhole tool 12 is described as a wireline downhole tool, it should be understood that any suitable delivery device can be used. For example, the downhole tool 12 can alternatively be delivered on a steel wire or through a coiled tubing as a part of a bottom hole assembly (BHA) of a drill string as a logging while drilling (LWD) tool, etc. For the purposes of the present disclosure, the downhole tool 12 can be any suitable downhole tool 12 that uses a high voltage power supply, for example, to generate nuclear radiation within a wellbore 16 (e.g., a downhole environment). As further discussed below, the downhole tool 12 can receive energy, for example, from an auxiliary power supply 24 or other storage / source with sufficient electrical energy, and convert the voltage for generating nuclear radiation. In addition, the supplied energy can be converted to a higher voltage within the wellbore 16, for example, via a high voltage power supply within or near the downhole tool 12.

[0032] Control signals 26 may be transmitted from the data processing system 28 to the downhole tool 12, and data signals 26 related to the response of the formation 14 may be returned from the downhole tool 12 to the data processing system 28. The processing system 28 may be any electronic data processing system 28 that may be used to perform the systems and methods of the present disclosure. For example, the data processing system 28 may include a processor 30 that may execute instructions stored in a memory 32 and / or a storage device 34. As such, the memory 32 and / or the storage device 34 of the data processing system 28 may be any suitable article of manufacture that may store instructions. The memory 32 and / or the storage device 34 may be a read-only memory (ROM), a random access memory (RAM), flash memory, an optical storage medium, or a hard drive, to name a few examples. The display 36 may be any suitable electronic display that may display images generated by the processor 30. The data processing system 28 may be a local component of the logging winch system 20 (e.g., within the downhole tool 12), a remote device that analyzes data from other logging winch systems 20, a device located proximate to the drilling operation, or any combination thereof. In some embodiments, the data processing system 28 may be a mobile computing device (eg, a tablet, smart phone, or laptop) or a server remote from the logging winch system 20 .

[0033] As mentioned above, Figure 2 As shown, the downhole tool 12 may include a high voltage power supply 38 and a radiation generator 40 housed within a housing 42. Although shown within the same housing 42, in some embodiments, the radiation generator 40 and the high voltage power supply 38 may be implemented in separate housings 42. The high voltage power supply 38 may include, for example, an input transformer 44 and a voltage multiplier 46. In some embodiments, the voltage multiplier 46 may include a diode 48 and / or a capacitor 50 arranged in a unipolar or bipolar ladder to generate a high voltage (e.g., greater than 50 kV, greater than 100 kV or greater) for output to the radiation generator 40, for example. The voltage multiplier 46 may include, for example, a Cockcroft-Walton voltage multiplier ladder, a derivative thereof, or any suitable circuit for generating a high voltage within the confines of the downhole tool 12. In some embodiments, a surge resistor 52 may be used between the high voltage power supply 38 and the radiation generator 40 to reduce or eliminate the effects of surges, for example, due to argon gas.

[0034] The radiation generator 40 can use the high voltage power generated by the high voltage power supply 38 to generate neutrons, gamma rays, X-rays, or other nuclear radiation. In some embodiments, the bias resistor 54 can cause the generated high voltage to drop across the entire length of the radiation generator 40 to generate a gradient electric field in which charged particles (e.g., electrons, ions, etc.) are accelerated. In one embodiment, the radiation generator 40 can accelerate particles into a target to generate nuclear radiation. In order to generate a potential difference, thereby generating an electric field in the radiation generator 40, a reference voltage (e.g., relative to ground) can be introduced, for example, through the housing 42. Keeping the housing 42 relatively grounded can also reduce electrical interference and / or discharge to the environment through the housing 42. However, because high voltage components (e.g., diodes 48, capacitors 50, resistors (e.g., surge resistors 52, bias resistors 54, or other resistors) and / or wires, solder joints and their leads) are used in such close proximity (e.g., less than three inches) to each other and the housing 42 relative to ground, electric field stresses may cause electrical events 56 (e.g., arcing, insulation breakdown, surface tracking, corona events, field emissions, etc.).

[0035] In some embodiments, an insulating gas 58 (e.g., air, sulfur hexafluoride (SF6), etc.) or a vacuum can be hermetically sealed within the downhole tool 12 to help prevent electrical events 56. Additionally or alternatively, an insulator 60 with a high dielectric strength (e.g., perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP) and / or plastic, Kapton or Teflon material) can be used along the inner edge of the housing 42. In some embodiments, the insulator 60 can extend from at least the beginning 62 of the voltage multiplier 46 to the end 64 of the voltage multiplier 46. In addition, the insulator 60 can also extend to the end 66 of the radiation generator 40. The insulator 60 can be fixed to the housing 42 of the downhole tool 12 and / or fixed to the internal components of the downhole tool 12 (e.g., the high voltage power supply 38, the radiation generator 40, other electrical shielding, etc.). In some embodiments, the insulator 60 can be implemented as a film wrapped around a shielding ring 68 around the internal components, such as Figure 3 shown.

[0036] The shielding ring 68 may be implemented in a coaxial arrangement around the voltage multiplier 46 and / or the radiation generator 40 to reduce the electric field stress of the electronic components near the downhole tool 12. In one embodiment, the shielding ring 68 may be generally conductive and may be made of any suitable metallic material or other conductor. In addition, in one embodiment, the shielding ring 68 may be made of a semiconductor plastic. The multiplier stage 70 of the voltage multiplier 46 and / or the radiator stage 72 of the radiation generator 40 may be electrically connected to each shielding ring 68. In this way, adjacent shielding rings 68 may be maintained at different electrical potentials. By electrically connecting each shielding ring 68 to the electrical components radially adjacent thereto, the shielding ring 68 may be maintained at the same or similar electrical potential (e.g., within 20 kV or within 40 kV) as the adjacent electrical components. By maintaining the shielding ring 68 at approximately the same electrical potential as the electrical components within the circumference of the shielding ring 68, the electric field and the corresponding electric field stress within the shielding ring 68 may be reduced. In addition, the reduced electric field may result in reduced electrical events 56.

[0037] In some embodiments, magnetic coupling from within the circumference of the shield ring 68 to the outside of the shield ring 68 may be desired. For example, the isolation transformer may be implemented as part of the circuit of the downhole tool 12, or the input transformer 44 may be partially enclosed within the shield ring 68. Thus, in one embodiment, the shield ring 68 may form a partial ring, such as having an arc angle greater than 180 degrees and less than 360 degrees, to increase the magnetic coupling from the inside of the shield ring 68 to the outside of the shield ring 68, while still minimizing the electric field stress within the shield ring 68.

[0038] To help illustrate the role of shield ring 68, Figure 4A and 4B Graphs 74, 76 of the electric field 78 around a sharp point 80 without and with the shield ring 68, respectively. For illustrative purposes, the sharp point 80 may represent a component of the downhole tool 12 that is under high voltage, such as a wire end, a corner of the radiation generator 40, or a weld. In general, the sharp point 80 causes increased electric field stress on a smooth surface and can be used to illustrate the effect on the electric field 78. Thus, electrical events 56 are more likely to occur at sharp points 80 and / or edges ... be used to represent a component of the downhole tool 12 that is under high voltage. Figure 4A The sharp point 80 in the diagram 74 of FIG. 7 is maintained at 400 kV and induces a large electric field 78 (e.g., greater than 100 megavolts per meter (MV / m)). When the shield ring 68 is implemented, as shown in FIG. Figure 4BAs shown in the diagram 76 of FIG. 74 , the electric field 78 around the cusp 80 is reduced. The reduction of the electric field 78 within the shield ring 68 can help protect the electrical components from electrical events 56, such as corona events and / or surface tracking, which in turn can increase the efficiency and / or life of the downhole tool 12. It will be appreciated that the diagrams 74 , 76 are given for illustrative purposes, and other electric fields 78 and / or voltages may occur depending on the implementation.

[0039] In one embodiment, a shield ring 68 may be implemented around the voltage multiplier 46 and the radiation generator 40. By reducing the electric field around the radiation generator 40, as described above, the electrical events 56 on the radiation generator 40 may be reduced. Additionally, the internal electric field of the radiation generator 40, such as used to accelerate charged particles, may be shielded from interference. In this way, the variability of radiation generation between individual downhole tools 12 may be reduced.

[0040] Figure 5 6 is a cross-sectional view of an exemplary downhole tool 12 that implements shield rings 68, insulators 60, insulating gas 58, and one or more spark gaps 82 between adjacent shield rings 68. The spark gaps 82 can help protect the electrical components of the downhole tool 12 in the event of an electrical event 56 (e.g., an arc). To prevent arcing within the electronic components, the spark gaps 82 can be shorted relative to a relative ground (e.g., the housing 42) when the voltage difference exceeds a given threshold. For example, if the voltage difference exceeds a threshold, such as between two shield rings 68, the arc can propagate to the relative ground via a series of electrodes, forming a spark gap 82 between them, rather than shorting the electrical components. In combination, the shield rings 68 and the spark gaps 82 help protect high voltage components from corona events, arcs, and / or current leakage, while also increasing the reliability and / or life of the downhole tool 12, while also allowing for a small size.

[0041] In some embodiments, the shield ring 68 may be potted (eg, surrounded and / or encapsulated) in a non-conductive or slightly conductive material to further reduce the risk of Figure 6B For example, the encapsulation material 84 may have an electric field stress greater than 10 -16 S / m conductivity and / or less than 10 -4 S / m, less than 10 -8 S / m or less than 10 -13S / m. Additionally, in some embodiments, the potting material 84 can be more conductive than the insulator 60 and / or the shielding ring 68. Additionally, the potting material 84 can have conductivity between the insulator 60 and the shielding ring 68. In one embodiment, a potting material 84 such as boron nitride with a silicone elastomer (e.g., Sylgard) can be implemented on the surface of the shielding ring 68, between adjacent shielding rings 68, and / or between the shielding ring 68 and the insulator 60. In this way, the potting material 84 can form a cylindrical tube on the outer edge of the shielding ring 68 and, in some embodiments, encapsulate the shielding ring 68. To help illustrate the effect of the potting material 84, Fig. 6A and 6B The shield ring 68 and the insulator 60 are shown in illustrations 86, 88 without and with the potting material 84, respectively. Figure 6B As shown in FIG88, compared with the case without potting material 84 Fig. 6A The electric field 78 surrounding the shield ring 68 potted with the potting material 84 is reduced compared to the illustration 86 of FIG. 8. The reduction of the electric field stress on the exterior of the shield ring 68 can further reduce the likelihood of electrical events 56 such as arcing. As will be appreciated, the illustrations 86, 88 are given for illustrative purposes, and other electric fields 78 may occur depending on the implementation.

[0042] Figure 7 90 is an exemplary flow chart of an example process for implementing the electrical protection and shielding discussed above within a downhole tool 12. In one embodiment, shield rings 68 may be placed around a high voltage power supply 38 or a portion thereof (e.g., voltage multiplier 46) and / or radiation generator 40 (process block 92). Each shield ring 68 may also be electrically connected to a multiplier stage 70 of voltage multiplier 46 and / or a generator stage 72 of radiation generator 40 (process block 94). Spark gaps 82 may be implemented between shield rings 68 (process block 96). Shield rings 68 may also be at least partially encapsulated in a potting material 84 (process block 98). Shield rings 68 implemented with or without potting may be wrapped in an insulator 60 (process block 100), for example, via a multi-layer insulating film. In addition, components of the downhole tool 12 may be sealed in a housing 42 (process block 102). Additionally, the area near the electrical components may be pressurized with an insulating gas 58 (process block 104). Although the flowchart 90 referenced above is shown in a given order, in some embodiments, the steps depicted may be reordered, changed, deleted and / or occur simultaneously. In addition, the flowchart 90 referenced is given as an illustrative tool, and further decision and / or process blocks may be added depending on the implementation.

[0043] In one or more embodiments, the radiation generator is configured to emit nuclear radiation, and the plurality of shielding rings surround at least the radiation generator.

[0044] In one or more embodiments, the radiation generator includes a plurality of generator stages, wherein each of the plurality of shielding rings is electrically coupled to a single generator stage of the plurality of generator stages.

[0045] In one or more embodiments, a method includes at least partially surrounding a high voltage power supply of a downhole tool with a plurality of shield rings, wherein the plurality of shield rings include an annular shape, wherein the plurality of shield rings are configured to reduce electric field stress within a diameter of the plurality of shield rings. Electrically coupling a spark gap electrode to at least two of the plurality of shield rings, wherein the spark gap electrode is configured to propagate an arc to a surface; and wrapping the plurality of shield rings with an insulator. An insulating gas is sealed within a housing of the downhole tool.

[0046] The method may also include electrically coupling each of the plurality of shielding rings surrounding the high voltage power supply to different electrical components of the high voltage power supply at different electrical potentials. The method may also include potting the plurality of shielding rings in a material comprising a first conductivity, wherein the first conductivity is greater than a second conductivity of the insulator. The method may also include wrapping the plurality of shielding rings with an insulator, including wrapping the potted plurality of shielding rings in a multilayer plastic film. The method may also at least partially surround a nuclear radiation generator of a downhole tool having a plurality of shielding rings; and electrically coupling each of the plurality of shielding rings surrounding the nuclear radiation generator to a nuclear radiation generator stage maintained at a different electrical potential, wherein the plurality of shielding rings are constructed to reduce electric field interference to the nuclear radiation generator within the diameter of the plurality of shielding rings surrounding the nuclear radiation generator.

[0047] In one or more embodiments, a downhole tool system may include a nuclear radiation generator configured to emit nuclear radiation; a high voltage power supply configured to convert input power from a first voltage to a second voltage and provide the second voltage to the nuclear radiation generator; a first plurality of coaxial shielding rings electrically coupled to a multiplier stage of the high voltage power supply; a second plurality of coaxial shielding rings electrically coupled to a generator stage of the nuclear radiation generator, wherein the generator stage is configured to generate an electric field within the nuclear radiation generator to accelerate charged particles to a target to generate nuclear radiation; a plurality of spark gaps between adjacent pairs of shielding rings of the first plurality of coaxial shielding rings, wherein the spark gaps are configured to propagate an arc in response to a voltage difference greater than a threshold between at least one pair of the adjacent pairs of shielding rings; and a plastic insulator surrounding the first plurality of coaxial shielding rings, the second plurality of coaxial shielding rings, or both.

[0048] In one or more embodiments, the system may include a potting material radially located between the plastic insulator and the first plurality of coaxial shielding rings.

[0049] In one or more embodiments, the potting material includes a cylindrical boron nitride tube having a silicone elastomer encapsulating a first plurality of coaxial shield rings.

[0050] The above specific embodiments have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the specific forms disclosed, but to cover modifications, equivalents, and alternative forms that fall within the spirit and scope of the present disclosure.

Claims

1. A downhole tool comprising: case; a voltage multiplier within the housing, the voltage multiplier configured to convert input power to the downhole tool from a first voltage to a second voltage, wherein the second voltage is greater than the first voltage; a plurality of shield rings surrounding at least the voltage multiplier and configured to reduce electric field stress within the downhole tool; an insulator located between the plurality of shielding rings and the housing; and A spark gap is provided between at least two shield rings of the plurality of shield rings.

2. The downhole tool according to claim 1, wherein: The voltage multiplier includes a plurality of multiplier stages, wherein each of the plurality of shield rings is electrically coupled to a single multiplier stage of the plurality of multiplier stages.

3. The downhole tool according to claim 1, wherein: The plurality of shielding rings include a metallic conductive material.

4. The downhole tool according to claim 1, wherein: The plurality of shield rings include a semiconductor material.

5. The downhole tool according to claim 1, wherein: The insulator includes a perfluoroalkoxy (PFA) film wrapped around an outer circumference of the plurality of shield rings.

6. The downhole tool according to claim 1, wherein: The housing is maintained at relative ground potential.

7. The downhole tool according to claim 1, wherein: The housing is sealed, and wherein the interior of the housing includes compressed sulfur hexafluoride (SF6) gas proximate the voltage multiplier.

8. The downhole tool according to claim 1, wherein: The plurality of shielding rings include at least one partial ring including an arc angle greater than 180 degrees and less than 360 degrees, wherein the at least one partial ring facilitates magnetic coupling from an interior of the at least one partial ring to an exterior of the at least one partial ring.

9. The downhole tool according to claim 1, wherein: The shield ring is potted in a potting material, wherein the potting material includes boron nitride.

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