A pulsed power drilling system and method for breaking a mineral substrate by use of microwave radiation for ionizing a fluid volume

Abstract

A pulsed power drilling system for breaking a mineral substrate and to a method for breaking a mineral substrate by passing a pulsed electrical current through the mineral substrate via at least one fluid volume that is at least partly ionized by use of microwave radiation. The disclosed pulsed power drilling system and method use microwave radiation for at least partly ionizing a fluid volume extending between an electrode and the surface of the mineral substrate and. The disclosed pulsed power drilling system and method may for example be applied in rock drilling, concrete processing, mineral processing, and continuous mining. The present disclosure further relates to a drill rig comprising a pulsed power drilling system and the use of a pulsed power drilling system.

Description

[0001] TITLE

[0002] A pulsed power drilling system and method for breaking a mineral substrate by use of microwave radiation for ionizing a fluid volume

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to a pulsed power drilling system for breaking a mineral substrate and to a method for breaking a mineral substrate by passing a pulsed electrical current through the mineral substrate via at least one fluid volume that is at least partly ionized by use of microwave radiation. The disclosed pulsed power drilling system and method use microwave radiation for at least partly ionizing a fluid volume extending between an electrode and the surface of the mineral substrate and. The disclosed pulsed power drilling system and method may for example be applied in rock drilling, concrete processing, mineral processing, and continuous mining. The present disclosure further relates to a drill rig comprising a pulsed power drilling system and the use of a pulsed power drilling system.

[0005] BACKGROUND

[0006] In the field of rock drilling, a new technology has emerged during the recent years, referred to as electro pulse boring (EPB), plasma channel drilling, pulsed plasma drilling, etc. The technology relies on mechanical electrodes creating contact with a rock material, and the application of a high voltage between the electrodes. The discharge occurring, if successful, penetrates the rock material and breaks loose small pieces. In some applications, an insulating fluid is proposed to prevent direct discharge between the electrodes. For most applications however, water has to be used for practical reasons, and in some cases even saline water. This makes it crucial to achieve a good contact between the electrodes and the rock material, since the discharge path through the water will otherwise become more attractive than the desired discharge path via the rock material.

[0007] A drill head usually comprises a plurality of electrodes. Since the rock surface is never ideally flat, one or more electrodes of the drill head are likely not to be in direct contact with the rock surface. Thus, some of the discharges are likely to occur directly between the electrodes, not penetrating the rock material. When the discharge does not penetrate the rock material, a loss of efficiency occurs. Ultimately, such a failed rock penetration will result in that no rock destruction is achieved.

[0008] There are typically relatively high requirements on the positioning accuracy of the drill head in that the electrodes of the drill head must be positioned in close proximity of the rock surface in order to achieve sufficiently good electrical contact with the surface of the rock material and allow for a high voltage current pulse generated by the pulsed power generator to pass between two electrodes of the drill head via the rock to be drilled. Individually suspended, spring-loaded electrodes, each with rock contact, have earlier been proposed. However, such electrodes are fragile and prone to wear.

[0009] SUMMARY

[0010] In light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks associated with conventional pulsed power drilling tools, such as non-penetrating discharge between the electrodes, low efficiency, high requirements on the positioning of the electrodes close to the surface of the mineral substrate to be drilled and excess wear of the electrodes.

[0011] A primary object of the present disclosure is to achieve an in at least some aspects improved pulsed power drilling system and method for pulsed power drilling. In particular, it is an object to achieve such a pulsed power drilling system and method which alleviate at least some of the drawbacks associated with prior art pulsed power drilling tools, such as non-penetrating discharge between the electrodes, low efficiency, high requirements on the positioning of the electrodes close to the surface of the mineral substrate to be drilled and excess wear of the electrodes.

[0012] Other objects of the present disclosure include the use of an improved pulsed power drilling system according to any of the embodiments disclosed and achieving an in at least some aspects improved drill rig comprising the improved pulsed power drilling system according to any of the embodiments disclosed.

[0013] According to a first aspect of the disclosure, at least the primary object is achieved by a pulsed power drilling system according to claim 1 , hereinafter also referred to as a drilling system. The drilling system is configured for passing a pulsed electrical current through a mineral substrate to break the mineral substrate and comprises: - a pulsed power generator for generating high voltage current pulses,

[0014] - a drill head comprising a plurality of electrodes comprising a solid electrode portion configured to be connected to the pulsed power generator, and

[0015] - an arrangement for generating microwave radiation used for at least partly and temporarily ionizing a fluid volume extending from a first solid electrode portion to a surface of the mineral substrate.

[0016] The present disclosure addresses at least some of the above-mentioned drawbacks associated with prior art pulsed power drilling tools by proposing a pulsed power drilling system comprising an arrangement for generating microwave radiation used for at least partly and temporarily ionizing at least a fluid volume extending from a solid electrode portion of a first electrode of the drill head to a surface of the mineral substrate, or rock surface.

[0017] In embodiments, the arrangement for generating microwave radiation comprises a microwave generator including a circuit for generating microwave radiation. The circuit may then be connected to a waveguide configured to transport the microwave radiation generated by the circuit in the direction of the fluid volume so as to allow the generated microwave radiation to be emitted in the fluid volume extending from the first solid electrode portion to a surface of the mineral substrate.

[0018] In embodiments, the pulsed power drilling system further comprises at least one microwave-transmissive device configured for positioning the focus point of the micro wave radiation, or micro wave beam, so that the focus point of the micro wave radiation is in the fluid volume extending between at least a solid electrode portion of a first electrode and the surface of the mineral substrate, or rock surface. The at least one microwave-transmissive device for positioning the focus point of the emitted microwave radiation may then comprise at least one lens, for example at least one dielectric lens.

[0019] In embodiments, the arrangement for generating microwave radiation comprises at least one microwave generator in the form of at least one of a magnetron, a solid- state generator, a maser, travelling wave tubes and frequency multipliers. The at least one microwave generator may then be configured to generated microwave radiation used for at least partly and temporarily ionizing at least a fluid volume extending from a solid electrode portion of a first electrode of the drill head to a surface of the mineral substrate prior to the generating, by the pulsed power generator, of at least one high voltage current pulse that is allowed to pass between the solid electrode portion of the first electrode and a second solid electrode portion of a second electrode of the drill head via the fluid volume and the mineral substrate.

[0020] In embodiments, the pulsed power drilling system comprises a pulsed power drilling tool including a pulsed power generator and a drill head, and the arrangement for generating microwave radiation comprises a microwave generator that is physically separated from the pulsed power drilling tool. The microwave generator may then be arranged and configured to emit microwave radiation in a fluid volume extending from a solid electrode portion of at least one of the electrodes of the drill head to a surface of the mineral substrate.

[0021] In embodiments, the solid electrode portion of at least one of the electrodes among the plurality of electrodes of the drill head is configured to be electrically connected to a micro wave generator of the arrangement for generating micro wave radiation. The solid electrode portion of the at least one electrode of the drill head may then be configured to function as an antenna for emitting the microwave radiation generated by the microwave generator.

[0022] In embodiments, the pulsed power drilling system further comprises a control system and a switching arrangement including at least one switch and the solid electrode portions of at least one of the plurality of electrodes of the drill head are arranged and configured to be electrically connected to a microwave generator of the arrangement for generating micro wave radiation.

[0023] The solid electrode portion of the at least one electrode among the plurality of electrodes may be further configured to also function as a waveguide for transporting the microwave radiation generated by the microwave generator to the fluid volume extending from the solid electrode portion of the at least one electrode to a surface of the mineral substrate.

[0024] In embodiments, the arrangement for generating microwave radiation comprises at least one microwave generator and the solid electrode portion of at least one of the electrodes among the plurality of electrodes is configured to be electrically connected to at least one microwave generator in the form of at least one of a magnetron, a solid-state generator, a maser, travelling wave tubes and frequency multipliers. The microwave generator may typically comprise a circuit, for example an oscillating circuit, for generating the microwave radiation.

[0025] In certain embodiments, the circuit is electrically connected to a waveguide configured to transport the microwave radiation generated by the circuit in the direction of a solid electrode portion of at least one of the electrodes functioning as a microwave antenna for emitting the microwave radiation. The waveguide may then be a dielectrically filled waveguide configured to transport the microwave radiation from the circuit for generating microwave radiation to the solid electrode portion of at least one of the electrodes.

[0026] In embodiments, the pulsed power drilling system may further comprise at least one microwave-transmissive device adapted for positioning the focus point of the microwave radiation emitted from the at least one solid electrode portion functioning as an antenna so that the focus point is between the solid electrode portion and the surface of the mineral substrate. The at least one microwave- transmissive device for positioning the focus point of the microwave radiation may then typically comprise at least one lens, for example a dielectric lens.

[0027] In aspects, the present disclosure relates to the use of a pulsed power drilling system according to any of the embodiments mentioned above.

[0028] In aspects, the present disclosure relates to a drill rig comprising a pulsed power drilling system according to any of the embodiments mentioned above. The drill rig may then be configured for breaking of a mineral substrate, such as in any one of rock drilling, concrete processing, mineral processing, and continuous mining.

[0029] In aspects, the present disclosure relates to an improved method for breaking a mineral substrate by use of a pulsed power drilling system comprising an arrangement for generating microwave radiation, a pulsed power generator and a drill head including a plurality of electrodes each comprising a solid electrode portion configured to be connected to the pulsed power generator, the improved method comprising:

[0030] - positioning the drill head so that the solid electrode portions of the plurality of electrodes of the drill head are at least in proximity of a surface of the mineral substrate; - generating, by use of an arrangement for generating microwave radiation, micro wave radiation;

[0031] - emitting the generated micro wave radiation in the fluid volume;

[0032] - generating, by use of a pulsed power generator, at least one high voltage current pulse; and

[0033] - passing the at least one high voltage current pulse between the solid electrode portion of the first electrode and a solid electrode portion of another electrode of the drill head via the fluid volume and the mineral substrate.

[0034] In embodiments, the pulsed power drilling system further comprises at least one microwave-transmissive device for positioning the focus point of microwave radiation, and the above method further comprises:

[0035] - positioning, by use of the at least one microwave-transmissive device, the focus point of the microwave radiation so that the focus point is between a solid electrode portion of at least the first electrode of the drill head and the surface of the mineral substrate.

[0036] In embodiments, the arrangement for generating microwave radiation includes a microwave generator comprising a circuit for generating microwave radiation and a waveguide where the circuit is electrically connected to the waveguide, and the above method further comprises the following step:

[0037] - transporting, through the waveguide, the microwave radiation generated by the circuit in the direction of the solid electrode portion of at least the first electrode among the plurality of electrodes of the drill head.

[0038] In embodiments, the arrangement for generating microwave radiation includes a microwave generator comprising a circuit for generating microwave radiation and at least a solid electrode portion of the first electrode among the pluralify of solid electrode portions of the drill head is configured to be connectable to the circuit of the microwave generator and arranged and configured to also function as an antenna, the step of emitting microwave radiation is comprising:

[0039] - emitting the microwave radiation generated by the circuit of the microwave generator from the solid electrode portion of at least the first electrode functioning as a microwave antenna. In embodiments, the pulsed power drilling system further comprises a control system and a switching arrangement including at least one switch and the solid electrode portions of a plurality of electrodes of the drill head are arranged and configured to be electrically connected to the circuit of the microwave generator, the method further comprises:

[0040] - controlling, by the control system, at least one switch of the switching arrangement so that at least a solid electrode portion of at least one of the electrodes functioning as a microwave antenna is electrically connected to a microwave generator, wherein the switching arrangement is controlled so that the solid electrode portion of at least one of the electrodes that is connected to a microwave generator includes the first electrode.

[0041] According to aspects of the technology disclosed, at least some of the above- mentioned drawbacks associated with conventional drilling systems are achieved by an improved pulsed power drilling system according to claim 1. The improved pulsed power drilling system is configured for passing a pulsed electrical current through a mineral substrate to break the mineral substrate. It comprises:

[0042] - a pulsed power generator for generating high voltage current pulses,

[0043] - a drill head comprising a plurality of electrodes comprising a solid electrode portion configured to be connected to the pulsed power generator, and

[0044] - an arrangement for generating microwave radiation used for at least partly and temporarily ionizing a fluid volume extending from a first solid electrode portion to a surface of the mineral substrate, so as to allow a high voltage current pulse generated by the pulsed power generator to pass between the first solid electrode portion and a second solid electrode portion of the drill head via the at least partly ionized fluid volume and the mineral substrate. The present disclosure also relates to use of a pulsed power drilling system for breaking of a mineral substrate, such as in any one of rock drilling, concrete processing, mineral processing, and continuous mining.

[0045] Advantages of the improved pulsed power drilling system comprising an arrangement for generating microwave radiation for transmission into a fluid volume between a solid electrode portion and the surface of the mineral substrate include that a region of higher conductivity can be achieved between the solid electrode portion and the mineral substrate.

[0046] The pulsed power drilling system of the present disclosure comprising an arrangement for generating microwave radiation for transmission into a fluid volume between a solid electrode portion and the surface of the mineral substrate may also enable that a good electrical contact may be achieved also with uneven substrate surfaces and / or when the solid electrode portions of the drill head are positioned a longer distance from the substrate surface than for conventional pulsed power drilling tolls, while the efficiency of the drilling process may be maintained or improved.

[0047] The pulsed power drilling system of the present disclosure may thus enable that the drill head with its solid electrode portions may be positioned a longer distance from the mineral substrate to be drilled than possible with other known drilling systems yet provide for sufficient electrical contact may be achieved with the substrate surfaces. Electrode wear as well as the risk for non-penetrating discharge between the electrodes can thereby be reduced, while the efficiency of the drilling process may be maintained or improved.

[0048] The pulsed power drilling system of the present disclosure comprising an arrangement for generating microwave radiation for transmission into a fluid volume between a solid electrode portion and the surface of the mineral substrate may also reduce the need for a plasma generator comprising a compressed gas supply system for supplying gas to the plasma generator.

[0049] Other advantages of the pulsed power drilling system according to the various embodiments of the pulsed power drilling system disclosed include that the at least partly ionized fluid volume(s) may easily be adapted to the dielectric properties of the mineral substrate by, for example, adjusting the power of the generated microwave radiation to thereby adjust the degree of ionization.

[0050] Further advantages and advantageous features of the disclosure are disclosed in the following description and in the dependent claims.

[0051] BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In the following, the technology disclosed will be described in detail, with reference to exemplifying embodiments and to the enclosed drawings.

[0053] In the drawings:

[0054] Fig. 1 schematically illustrates a pulsed power drilling system according to an embodiment of the disclosure,

[0055] Fig. 2 schematically illustrates a pulsed power drilling system according to an embodiment of the disclosure,

[0056] Fig. 3 schematically illustrates a pulsed power drilling system according to an embodiment of the disclosure,

[0057] Fig. 4 schematically illustrates a pulsed power drilling system according to an embodiment of the disclosure,

[0058] Fig. 5 schematically illustrates a pulsed power drilling system according to an embodiment of the disclosure,

[0059] Fig. 6 schematically illustrates a pulsed power drilling system according to an embodiment of the disclosure,

[0060] Fig. 7 is a flow-chart illustrating steps of a method according to an embodiment of the disclosure, and

[0061] Fig. 8 is a rock drilling machine, or drill rig, configured for comprising any of the pulsed power drilling system shown in Figs. 1, 2, 3, 4, 5, and 6.

[0062] The drawings show diagrammatic, exemplifying embodiments of the present disclosure and are thus not necessarily drawn to scale. It shall be understood that the embodiments shown and described are exemplifying and that the disclosure is not limited to these embodiments. It shall also be noted that some details in the drawings may be exaggerated in order to better describe and illustrate the disclosure. Like reference characters refer to like elements throughout the description, unless expressed otherwise.

[0063] DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE DISCLOSURE

[0064] The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.

[0065] The present disclosure addresses at least some of the above-mentioned drawbacks associated with prior art pulsed power drilling tools by proposing a pulsed power drilling system comprising an arrangement for generating microwave radiation used for at least partly and temporarily ionizing at least a fluid volume extending from a solid electrode portion of a first electrode of the drill head to a surface of the mineral substrate, or rock surface.

[0066] The technology disclosed relates to a pulsed power drilling system for breaking a mineral substrate and to a method for breaking a mineral substrate by passing a high voltage current pulse for breaking the mineral substrate through the mineral substrate via at least one fluid volume that is already at least partly ionized by use of microwave radiation transmitted into the fluid volume. The disclosed pulsed power drilling system and method use microwave radiation for at least partly ionizing a fluid volume extending between a solid portion of an electrode of the drill head and the surface of the mineral substrate. The disclosed pulsed power drilling system and method may for example be applied in rock drilling, concrete processing, mineral processing, and continuous mining.

[0067] The technology disclosed further relates to a drill rig comprising a pulsed power drilling system configured to use microwave radiation for at least partly ionizing at least one fluid volume prior to passing a high voltage current pulse through the mineral substrate via the fluid volume and the use of such a pulsed power drilling system for breaking a mineral substrate. The at least one fluid volume is at least partly ionized by use of microwave radiation generated by an arrangement for generating microwave radiation. High voltage current pulses generated by the pulsed power generator pass between a solid electrode portion of a first electrode and a solid electrode portion of a second electrode of the drill head via the at least one fluid volume and the mineral substrate. The pulsed power drilling system may then generate high voltage current pulses that are allowed to pass from the solid electrode portion of the first electrode to the solid electrode portion of the second electrode, or vice versa.

[0068] The pulsed power drilling system may in various embodiment comprise a drill head with three or more electrodes each comprising a solid electrode portion and the system may then be configured to selectively allow for that high voltage current pulses may pass from a first solid electrode portion of any of the three or more electrodes to a second solid electrode portion of any of the other electrodes of the drill head via at least one fluid volume that is at least partly ionized by use of microwave radiation and a mineral substrate. The same pulsed power system may also be configured to selectively allow for that high voltage current pulses may pass from the second solid electrode portion to the first solid electrode portion via at least one fluid volume that is at least partly ionized by use of microwave radiation and a mineral substrate. For example, the pulsed power drilling system may comprise two microwave generators each associated with and configured to be connected to at least one of the at least three electrodes so that a fluid volume extending between the respective two solid electrode portions selected for carrying the discharge of the high voltage current pulse and the substrate surface is at least partly ionized by use of the microwave radiation so that two at least partly ionized channels are created in the at least one fluid volume between the drill head and the substrate surface.

[0069] In embodiments, the pulsed power drilling system comprises at least three electrodes and is configured to allow for that high voltage current pulses may pass from a solid electrode portion of at least any of three of the at least three to any of the other at least two other electrodes via at least one fluid volume that is at least partly ionized by use of microwave radiation and a mineral substrate, or vice versa.

[0070] The microwave radiation is emitted in the at least one fluid volume for the purpose of temporarily heating up the at least one fluid volume. The heat added to the at least one fluid volume by the transmission of the microwave radiation generated by at least one microwave generator is at least indirectly contributing to the process of creating an at least partly ionized fluid volume, or channel, between the solid electrode portion of a first electrode of the drill head to a surface of the mineral substrate and, optionally, also an at least partly ionized fluid volume extending between the solid electrode portion of the second electrode to a surface of the mineral substrate.

[0071] The technology disclosed proposes a pulsed power drilling system that is configured for passing a pulsed electrical current through a mineral substrate to break the mineral substrate. The pulsed power drilling system comprises a pulsed power generator for generating high voltage current pulses, a drill head comprising a plurality of electrodes that each typically comprises a solid electrode portion configured to be connected to the pulsed power generator, and an arrangement for generating microwave radiation used for at least partly and temporarily ionizing a fluid volume extending from a first solid electrode portion to a surface of the mineral substrate. The pulsed power drilling system thereby allows for at least one high voltage current pulse generated by the pulsed power generator to pass between the first solid electrode portion and a second solid electrode portion of the drill head via the at least partly ionized fluid volume and the mineral substrate.

[0072] The arrangement for generating microwave radiation comprises at least one microwave generator each including a circuit for generating microwave radiation. The at least one circuit may be configured to be electrically connected directly to at least one of the electrodes of the drill head or the at least one circuit is configured to be connected to at least one of the electrodes of the drill head via a waveguide configured to transport the microwave radiation generated by the circuit in the direction of a fluid volume present in front of the respective at least one electrode so as to allow the generated microwave radiation to be emitted in the fluid volume extending from a solid electrode portion of the at least one electrode to a surface of the mineral substrate.

[0073] In embodiments, the fluid volume present in front of the front end of the drill head may then be extending both from a solid electrode portion of a first electrode to the surface of the mineral substrate and from a solid electrode portion of a second electrode to the surface of the mineral substrate and the fluid volume is at least partly ionized by use of microwave radiation generated by at least one arrangement for generating microwave radiation in order to create both a first at least partly ionizied fluid volume extending between the solid electrode portion of the first electrode and the mineral substrate and a second at least partly ionizied fluid volume extending between the solid electrode portion of the second electrode and the mineral substrate. The microwave radiation, which is generated by at least one microwave generator of the arrangement, is transmitted into the at least one fluid volume for the purpose of temporarily heating up the fluid volume where the heat added to the fluid volume by the microwave radiation is at least indirectly contributing to the process of creating an at least partly ionized first channel extending between the solid electrode portion of the first electrode to a surface of the mineral substrate and an at least partly ionized second channel extending between the solid electrode portion of the second electrode to a surface of the mineral substrate. The fluid volume, for example water, may then be generated by the pulsed power drilling system and / or be naturally present between the drill head and the surface of the mineral substrate to be drilled.

[0074] In certain embodiments, both a first fluid volume extending from a solid electrode portion of a first electrode to the surface of the mineral substrate and a second fluid volume extending from a second solid electrode portion of a second electrode to the surface of the mineral substrate are at least partly ionized by use of the microwave radiation generated by the arrangement for generating microwave radiation.

[0075] The arrangement for generating microwave radiation may then comprise at least one microwave generator in the form of at least one of a magnetron, a solid-state generator, a maser, travelling wave tubes and frequency multipliers. The at least one microwave generator may then be configured to generate microwave radiation used for at least partly and temporarily ionizing at least a fluid volume extending from a solid electrode portion of a first electrode of the drill head to a surface of the mineral substrate prior to the generating, by the pulsed power generator, of at least one high voltage current pulse that is allowed to pass between the solid electrode portion of the first electrode and a second solid electrode portion of a second electrode of the drill head via the fluid volume and the mineral substrate. The fluid volume is heated by the microwave radiation generated by the microwave generator and emitted in the fluid volume. The heating of the fluid volume by transmitting the microwave radiation into the fluid volume then contributes to the process of partly and temporarily ionizing the fluid volume, so as to allow and guide the at least one high voltage current pulse to pass between the solid electrode portion of the first electrode and a second solid electrode portion of a second electrode of the drill head via the fluid volume and the mineral substrate. The microwave radiation generated by the at least one arrangement for generating microwave radiation is used for at least partly and temporarily ionizing a fluid volume extending from a solid electrode portion of an electrode of the drill head to a surface of the mineral substrate so that a region of higher conductivity can be achieved between the solid electrode portion and the mineral substrate. The at least partly and temporarily ionized fluid volume will have a substantially higher conductivity in comparison with, for example, non-ionized fluid surrounding it, which means that the high voltage current pulse will pass through the ionized fluid volume from the solid electrode portion to the mineral substrate.

[0076] The transmission of microwave radiation into the fluid volume provides for a fluid volume that is at least partly ionized and where at least portions of the fluid volume has a higher conductivity between the solid electrode portion and the mineral substrate to thereby achieve an improved electrical contact between the solid electrode portion and the mineral substrate, which electrical contact improves the guidance of the current into the mineral substrate without “leaking” into the surrounding environment of the fluid volume. The improved electrical contact provided in this way is not dependent on any mechanical contact between the solid electrode portion and the mineral substrate. Thus, a good electrical contact may be achieved also with uneven substrate surfaces and / or when the solid electrode portions of the drill head are positioned a longer distance from the substrate surface, while the efficiency of the drilling process may be maintained or improved.

[0077] A pulsed power drill system that comprises an arrangement for emitting microwave radiation into the fluid volume may further enable that the drill head with its solid electrode portions may be positioned a longer distance from the mineral substrate to be drilled than possible with other known drilling tools yet provide for sufficient electrical contact may be achieved with the substrate surfaces. Electrode wear as well as the risk for non-penetrating discharge between the electrodes can thereby be reduced, while the efficiency of the drilling process may be improved.

[0078] The introduction of a pulsed power drilling system that comprises an arrangement for emitting microwave radiation into the fluid volume extending between the solid electrode portion and the mineral substrate may also reduce the need for a plasma generator that comprises a compressed gas supply system for supplying compressed gas to the plasma generator configured to ionize the compressed gas to generate a plasma and where at least one ionized fluid volume that is subsequently supplied to a volume in front of a solid electrode portion of an electrode of the drill head is being formed by the plasma.

[0079] Other advantages of the pulsed power drilling system and method according to the technology disclosed include that the at least one fluid volume that is at least partly ionized by use of microwave radiation may easily be adapted to the dielectric properties of the mineral substrate by, e.g., adjusting the power of the microwave radiation and thereby the degree of ionization, and / or by adjusting the flow of fluid, for example to change a diameter of the fluid volume. The degree of ionization that is achieved by use of microwave radiation times the flow will result in a certain conductivity of the at least partly ionized fluid, which may be exploited to reduce power reflectance at the surface of the mineral substrate. The possibilities for impedance matching are thus improved.

[0080] In embodiments, the solid electrode portion of at least one of the electrodes among the plurality of electrodes of the drill head is configured to be electrically connected to a micro wave generator of the arrangement for generating micro wave radiation. In embodiments, the microwave generator may be physically separated from the electrodes of the drill head or the solid electrode portion of the at least one electrode of the drill head may be configured to also function as an antenna for emitting the microwave radiation generated by the microwave generator.

[0081] In embodiments, the solid electrode portion of at least a plurality of the electrodes of the drill head is configured to be electrically connected to their respective microwave generator of the arrangement for generating microwave radiation. Thus, for an electrode pair in which a fluid volume is supplied or present between both the first and the second solid electrode portions and the mineral substrate, respectively, the first and second electrodes may comprise their own microwave generator for generating microwave radiation used for at least partly and temporarily ionizing the fluid volume extending between the respective electrode and the surface of the mineral substrate.

[0082] In embodiments, a first and a second electrode is connected to their respective microwave generator, for example their respective solid-state microwave generator, and is each configured to function as a microwave antenna used for transmitting microwave radiation generated by their respective microwave generator in the direction of the surface of the mineral substrate to be drilled. Both the first and the second electrode are then configured to be electrically connected to the pulsed power generator and to carry a discharge of a high voltage current pulse generated by the pulsed power generator.

[0083] The pulsed power drilling system may further comprise a control system and a switching arrangement including at least one switch and the solid electrode portions of at least one of the plurality of electrodes of the drill head are arranged and configured to be electrically connected to a pulsed power generator of the pulsed power drilling system. The control system may then be configured to control the at least one switch to temporarily connect the solid electrode portion of two of the electrodes of the drill head to the pulsed generator to thereby allow for at least one high voltage current pulse to pass between the solid portions of the two electrodes via at least one fluid volume that is at least partly ionized by use of micro wave radiation and the mineral substrate. The pulsed power drilling system may further comprise a control system and a switching arrangement including at least one switch and the solid electrode portions of at least one of the plurality of electrodes of the drill head are arranged and configured to be electrically connected to a micro wave generator of the arrangement for generating micro wave radiation. The control system may then be configured to control the at least one switch to temporarily connect the solid electrode portion of one or two of the electrodes of the drill head to their respective microwave generator to thereby allow for transmission of the microwave radiation generated by the microwave generator into a fluid volume extending from at least one of the two electrodes to the substrate surface.

[0084] In certain embodiments, the pulsed power system comprises a plurality of microwave generators and both the solid electrode portion of the first electrode and the solid electrode portion of the second electrode are configured to be connectable to their respective microwave generator. The control system of the pulsed power system may then be configured to control a switching arrangement and the opening and closing of at least one switch to control whether microwave radiation from the respective microwave generator is transmitting microwave radiation into a fluid volume associated with the solid electrode portion of the respective electrode.

[0085] In certain embodiments, both the solid electrode portion of the first electrode and the solid electrode portion of the second electrode are configured to be connectable to a common microwave generator. The control system of the pulsed power system may then be configured to control a switching arrangement to thereby control whether microwave radiation from the common microwave generator is transmitting microwave radiation into a fluid volume associated with the solid electrode portion of the respective electrode.

[0086] In aspects, the technology disclosed relates to a method for breaking a mineral substrate by passing a pulsed electrical current through the mineral substrate by use of a pulsed power drilling system comprising a pulsed power generator and a drill head comprising a plurality of electrodes each comprising a solid electrode portion configured to be connected to the pulsed power generator, the method comprising:

[0087] - positioning the drill head so that the plurality of solid electrode portions are at least in proximity of a surface of the mineral substrate,

[0088] - generating, by use of the microwave generator, microwave radiation used for at least partly and temporarily ionizing a fluid volume extending from a solid electrode portion of a first electrode among the plurality of electrodes to a surface of the mineral substrate,

[0089] - emitting the generated micro wave radiation in the fluid volume,

[0090] - generating, by use of the pulsed power generator, a high voltage current pulse, and

[0091] - passing the high voltage current pulse between the solid electrode portion of the first electrode and a solid electrode portion of a second electrode of the drill head via the at least partly ionized fluid volume and the mineral substrate.

[0092] In aspects and with the purpose of alleviating at least some of the drawbacks associated with prior art pulsed power drilling tools, the primary object of the present disclosure relates to an improved method for breaking a mineral substrate by use of a pulsed power drilling system comprising a pulsed power generator and a drill head including a plurality of electrodes comprising a solid electrode portion configured to be connected to the pulsed power generator, the improved method comprising:

[0093] - positioning the drill head so that the solid electrode portions of the plurality of electrodes of the drill head are at least in proximity of a surface of the mineral substrate;

[0094] - generating, by use of an arrangement for generating microwave radiation of the pulsed power drilling system, microwave radiation used for at least partly and temporarily ionizing a fluid volume extending from a solid electrode portion of at least one of the electrodes of the plurality of electrodes of the drill head to a surface of the mineral substrate;

[0095] - emitting the generated micro wave radiation in the fluid volume;

[0096] - generating, by use of the pulsed power generator, at least one high voltage current pulse; and

[0097] - passing the at least one high voltage current pulse between the solid electrode portion of a first electrode and a solid electrode portion of a second electrode among the plurality of electrodes of the drill head via the at least partly and temporarily ionized fluid volume and the mineral substrate.

[0098] The method may comprise emitting the microwave radiation in the fluid volume prior to passing the at least one high voltage current pulse between the solid electrode portion of the first electrode and a solid electrode portion of the second electrode.

[0099] In embodiments, the above steps of generating and emitting microwave radiation comprise:

[0100] - generating and emitting microwave radiation used for at least partly and temporarily ionizing both a first fluid volume extending from a solid electrode portion of the first electrode to a surface of the mineral substrate and a second fluid volume extending from a solid electrode portion of a second electrode of the drill head to a surface of the mineral substrate, so as to allow the high voltage current pulse generated by the pulsed power generator to pass between the solid electrode portion of the first electrode and the solid electrode portion of the second electrode via the at least partly ionized first fluid volume, the mineral substrate and the at least partly ionized second fluid volume.

[0101] In embodiments, the pulsed power drilling system further comprises a control system and a switching arrangement including at least one switch and the solid electrode portion of a first electrode of the drill head is arranged and configured to be electrically connected to the pulsed power generator, the method further comprises:

[0102] - generating, by use of an arrangement for generating microwave radiation, microwave radiation used for at least partly and temporarily ionizing a fluid volume extending from a solid electrode portion of the first electrode of the drill head to a surface of the mineral substrate; - emitting the generated micro wave radiation in the fluid volume;

[0103] - switching, under the control of the control system, at least one switch of the switching arrangement so that the solid electrode portion of the first electrode is electrically connected to the pulsed power generator of the pulsed power drilling system;

[0104] - generating, by use of the pulsed power generator, at least one high voltage current pulse; and

[0105] - passing the at least one high voltage current pulse between the solid electrode portion of the first electrode and a solid electrode portion of a second electrode of the drill head via the fluid volume and the mineral substrate, wherein at least a portion of the generated microwave radiation is emitted into the fluid volume prior to passing the high voltage current pulse between the solid electrode portion of the first electrode and a solid electrode portion of the second electrode via the at least partly ionized fluid volume and the mineral substrate.

[0106] In embodiments, the pulsed power drilling system further comprises a control system and a switching arrangement including at least one switch and the solid electrode portion of a first electrode of the drill head is arranged and configured to be electrically connected to the circuit of the microwave generator, the method further comprises:

[0107] - switching, under the control of the control system, at least one switch of the switching arrangement so that the solid electrode portion of the first electrode is electrically connected to a microwave generator of the pulsed power drilling system;

[0108] - generating, by use of an arrangement for generating microwave radiation, microwave radiation used for at least partly and temporarily ionizing a fluid volume extending from a solid electrode portion of the first electrode of the drill head to a surface of the mineral substrate;

[0109] - emitting the generated micro wave radiation in the fluid volume;

[0110] - generating, by use of a pulsed power generator, a high voltage current pulse; and

[0111] - passing the high voltage current pulse between the solid electrode portion of the first electrode and a solid electrode portion of a second electrode of the drill head via the fluid volume and the mineral substrate, wherein at least a portion of the generated microwave radiation is emitted in the fluid volume prior to passing the high voltage current pulse between the solid electrode portion of the first electrode and a solid electrode portion of the second electrode via the at least partly ionized fluid volume and the mineral substrate.

[0112] In embodiments, the pulsed power drilling system further comprises a control system and a switching arrangement including at least one switch and the solid electrode portions of a plurality of electrodes of the drill head are arranged and configured to be electrically connected to the circuit of their respective microwave generator, the method further comprises:

[0113] - switching, under the control of the control system, at least one switch of the switching arrangement so that a solid electrode portion of both the first electrode and a solid electrode portion of a second electrode, both configured to function as a microwave antenna, are electrically connected to their respective microwave generator of the pulsed power drilling system;

[0114] - generating, by use of the respective microwave generator of an arrangement for generating microwave radiation, microwave radiation used for at least partly and temporarily ionizing both a first fluid volume extending from a solid electrode portion of the first electrode of the drill head to a surface of the mineral substrate and for at least partly and temporarily ionizing a second fluid volume extending from a solid electrode portion of a second electrode of the drill head to a surface of the mineral substrate;

[0115] - emitting, from the respective solid electrode portion of the first and second electrode, the generated micro wave radiation in the respective first and second fluid volume;

[0116] - generating, by use of a pulsed power generator, a high voltage current pulse; and

[0117] - passing the high voltage current pulse between the solid electrode portion of the first electrode and a solid electrode portion of the second electrode of the drill head via the first and second fluid volumes and the mineral substrate, wherein at least a portion of the microwave radiation is emitted in the respective first and second fluid volume prior to passing the high voltage current pulse between the solid electrode portion of the first electrode and a solid electrode portion of the second electrode via an at least partly ionized first channel in the first fluid volume, the mineral substrate and an at least partly ionized second channel in the second fluid volume.

[0118] In embodiments, the arrangement for generating microwave radiation includes a microwave generator comprising a circuit for generating microwave radiation, and at least the solid electrode portion of at least one of the electrodes among the plurality of electrodes of the drill head is electrically connected to the circuit of the microwave generator to thereby be arranged and configured to also function as a waveguide for leading, or transporting, the microwave radiation generated by the circuit of the microwave generator, said method further comprising:

[0119] - transporting the generated microwave radiation via the solid electrode portion of at least one of the electrodes of the drill head so that the microwave radiation is travelling along the at least one solid electrode portion to be emitted in the fluid volume extending from the solid electrode portion of the at least one electrode to a surface of the mineral substrate.

[0120] In embodiments, the method further comprises:

[0121] - supplying a shielding fluid to a region between the electrodes at least during the action of passing the high voltage current pulse from the first electrode to the second electrode.

[0122] The high voltage current pulse will typically create an at least partly ionized channel in the mineral substrate, via which channel the current pulse passes to the other electrode. In order for the current to pass between the electrodes, there has to be a difference in electric potential between the electrodes. In embodiments, the at least one pair of a first electrode and a second electrode may for this purpose comprise a positive electrode and a negative electrode, but it is also possible to, e.g., provide one positive or negative electrode and one electrode at zero potential. In embodiments, a plurality of the electrodes of the drill head are configured to have both a positive potential and a negative potential.

[0123] The term “ionized fluid” or “partly ionized fluid” is herein to be understood as a fluid volume, for example a channel in a fluid volume, containing both positively and negatively charged particles. The term “ionized fluid” is further to be understood as encompassing ionized gas and ionized liquid, as well as fluids containing electrically charged particles of solid matter, such as nanoparticles or microparticles.

[0124] In aspects and embodiments, the pulsed power drilling system may be configured for transmitting microwave radiation only into a first fluid volume extending at least from a first solid electrode portion to the surface of the mineral substrate in order to generate heat in the fluid volume that contributes to the process of at least partly and temporarily ionizing the fluid volume, while a second fluid volume extending at least from a second solid electrode portion to the surface of the mineral substrate is not partly ionized by use of microwave radiation that is transmitted into the second fluid volume. The drill head may then comprise a plurality of electrodes comprising a solid electrode portion configured to be connected to the pulsed power generator and an arrangement for generating microwave radiation used for at least partly and temporarily ionizing a first fluid volume extending from a first solid electrode portion to a surface of the mineral substrate, so as to allow a high voltage current pulse generated by the pulsed power generator to pass between the first solid electrode portion and a second solid electrode portion of the drill head via the at least partly ionized first fluid volume and the mineral substrate. In this case, no mechanical contact between either one of the solid electrode portions and the mineral substrate is needed, and thus electrode wear can be further reduced.

[0125] In embodiments, the pulsed power drilling system further comprises a fluid supply system for supplying a shielding fluid to a region between the drill head and the mineral substrate. The shielding fluid may be any fluid that may serve to shield the fluid volume or volumes from each other and / or from one or more solid electrode portions of one or more other electrodes. The shielding fluid may preferably be a different fluid than the fluid of the ionized fluid volumes. The shielding fluid may, e.g., be a flushing liquid, such as water, which is typically supplied during the drilling operation.

[0126] The pulsed power drilling system may then be configured for transmitting microwave radiation into both a first fluid volume extending at least from the first solid electrode portion to the surface of the mineral substrate, and into a second fluid volume extending at least from the second solid electrode portion to the surface of the mineral substrate, the first fluid volume being isolated from the second fluid volume so as to allow the high voltage current pulse to pass via the first ionized fluid volume, the mineral substrate and the second ionized fluid volume. In this case, no mechanical contact between either one of the solid electrode portions and the mineral substrate is needed, and thus electrode wear can be further reduced. The electrodes thereby become more robust and less expensive. The isolation between the first ionized fluid volume and the second ionized fluid volume may, e.g., be achieved by supplying a shielding fluid, such as a liquid, with a relatively poor conductivity in comparison with the ionized fluid volumes and the solid electrode portions. The shielding fluid may, e.g., be a flushing fluid, such as water or even saline water.

[0127] Optionally, the second solid electrode portion may be configured to be mechanically applied against the mineral substrate, wherein the at least one ionized first fluid volume is isolated from the second solid electrode portion. By mechanically applying the second solid electrode portion against the mineral substrate, correct positioning of the first solid electrode portion with respect to the mineral substrate is facilitated, i.e., positioning at a distance that will provide optimal conditions for creating the at least partly ionized fluid volume. The isolation between the ionized first fluid volume and the second solid electrode portion may be achieved as explained above.

[0128] In certain embodiments, the pulsed power drilling system of the present disclosure further comprises at least one ionization device including at least one plasma generator. The pulsed drilling system may then further comprise a compressed gas supply system for supplying compressed gas to the at least one plasma generator. The at least one plasma generator may then be configured to ionize the compressed gas to generate a plasma, where the at least one ionized fluid volume is being formed by the plasma. The at least one ionized fluid volume may then be supplied in front of the front end of the drill head and further ionized by use of the heating of the at least one ionized fluid volume from the transmission / emission of the microwave radiation into the least one ionized fluid volume where the microwave radiation is generated by a microwave generator of the arrangement for generating microwave radiation. Optionally, at least the first electrode comprises a first plasma generator, and further optionally the second electrode comprises a second plasma generator. Thus, for an electrode pair, for example an electrode pair selected from at least three electrodes of the drill head, in which ionized fluid volumes are generated between both the first and the second solid electrode portions and the mineral substrate, respectively, the first and second electrodes may comprise their own plasma generators. The at least one arrangement for generating microwave radiation may each comprise a microwave generator including a circuit for generating microwave radiation. The circuit may then be connected to a waveguide configured to transport the microwave radiation generated by the circuit in the direction of the fluid volume that is present in front of the solid electrode portion of the respective electrode so as to allow the generated microwave radiation to be emitted in the fluid volume extending from the respective solid electrode portion to a surface of the mineral substrate.

[0129] The respective at least one arrangement for generating microwave radiation of a pulsed power drilling system comprising at least two electrodes may further comprise at least one microwave-transmissive device and / or aperture configured for positioning the focus point of the microwave radiation so that the focus point of the microwave radiation is in the fluid volume extending between the solid electrode portion of the respective at least one electrode and the surface of the mineral substrate. Thus, the at least one arrangement for generating and emitting microwave radiation may then comprise focusing means for positioning the focus point of the emitted microwave radiation. The focusing means may comprise at least one of an aperture and a microwave-transmissive device including at least one lens, for example a dielectric lens.

[0130] The respective of the at least one arrangement for generating and emitting microwave radiation may then comprise at least one microwave generator in the form of at least one of a magnetron, a solid-state microwave generator, a maser, travelling wave tubes and frequency multipliers.

[0131] In embodiments, the arrangement for generating microwave radiation of the pulsed power drilling system may then comprise a microwave generator that is physically separated from the pulsed power drilling tool and configured to emit microwave radiation in the fluid volume extending from the solid electrode portion of the respective at least one electrode to a surface of the mineral substrate.

[0132] In embodiments, the respective at least one arrangement for generating microwave radiation of the pulsed power drilling system may then comprise a microwave generator which is physically separated from the pulsed power drilling tool and configured to emit microwave radiation in the fluid volume extending from the solid electrode portion of the respective at least one electrode to a surface of the mineral substrate. The at least one arrangement for generating microwave radiation is then a separate device from the pulsed power drilling tool and comprises a circuit for generating microwave radiation, a waveguide configured to transport the microwave radiation generated by the circuit in the direction of the fluid volume and at least one microwave-transmissive device and / or aperture configured for positioning the focus point of the microwave radiation. The circuit is typically arranged at a first end of the waveguide and the at least one microwave- transmissive device and / or aperture is arranged at a second end of the waveguide and configured to position the focus point of the microwave radiation transported through the waveguide so that the focus point of the microwave radiation is in the fluid volume extending between the solid electrode portion of the respective at least one electrode and the surface of the mineral substrate.

[0133] The solid electrode portion of the respective at least one electrode among the plurality of electrodes of the drill head may then be configured to be electrically connected to a microwave generator. The solid electrode portion of the respective at least one electrode may then be further configured to also function as an antenna for emitting the microwave radiation generated by the microwave generator.

[0134] The solid electrode portion of the respective at least one electrode among the plurality of electrodes of the drill head may then be further configured to also function as a waveguide for leading / transporting the microwave radiation generated by the respective at least one microwave generator to the fluid volume extending from the solid electrode portion of the respective at least one electrode to a surface of the mineral substrate. The at least one microwave generator may then be at least one of a magnetron, a solid-state microwave generator, a maser, travelling wave tubes and frequency multipliers.

[0135] The pulsed power drilling system of the technology disclosed may comprise at least one arrangement for generating microwave radiation including a circuit for generating microwave radiation, and, optionally, a waveguide configured to transport the microwave radiation generated by the circuit in the direction of the fluid volume and at least one microwave-transmissive device or aperture configured for positioning the focus point of the microwave radiation.

[0136] The circuit may then be arranged at a first end of a waveguide and a solid electrode portion of a first electrode is arranged at a second end of the waveguide so that the solid electrode portion is thereby arranged and configured to lead the microwave radiation to at least one microwave-transmissive device or aperture configured to position the focus point of the microwave radiation transported through the waveguide and then lead via the solid electrode portion so that the focus point of the microwave radiation is in the fluid volume extending between the solid electrode portion and the surface of the mineral substrate.

[0137] The pulsed power drilling system may then further comprise at least one device for generating at least one fluid volume extending from a solid electrode portion of at least one of the electrodes of the drill head to a surface of the mineral substrate.

[0138] The at least one device for generating a fluid volume may then be configured to generate a first fluid volume extending from the solid electrode portion of a first electrode to the surface of the mineral substrate and a second fluid volume extending from a solid electrode portion of a second electrode to the surface of the mineral substrate, where the first fluid volume being isolated from the second fluid volume so as to allow the high voltage current pulse to pass via the first volume, the mineral substrate and the second fluid volume. At least one of the first and second volume may then be at least partly ionized by use of microwave radiation generated and emitted by the at least one arrangement for generating microwave radiation.

[0139] The at least one arrangement for generating microwave radiation may then be configured to at least partly and temporarily ionizing both a first fluid volume extending from the first solid electrode portion of a first electrode to a surface of the mineral substrate and a second fluid volume extending from the second solid electrode portion of a second electrode to a surface of the mineral substrate, so as to allow a high voltage current pulse generated by the pulsed power generator to pass between the first solid electrode portion and the second solid electrode portion via the at least partly ionized first fluid volume, the mineral substrate and the at least partly ionized second fluid volume.

[0140] Fig. 1 schematically illustrates an example embodiment of a pulsed power drilling system 100 configured for passing a pulsed electrical current through a mineral substrate 400 to break it. The drilling tool 100 has a pulsed power generator 110 for generating high voltage current pulses, and a drill head 120 extending in an axial direction of the drilling tool 100 between a front end 121, configured to be positioned near or at a surface of the mineral substrate 400, and a rear end 122. The pulsed power generator 110 illustrated in Fig. 1 comprises a pulse transformer 112 in the form of a bank of capacitors, connected to an alternating current (AC) power supply 113 via a transformer 111. Electrodes 200 and 200’ are selected and connected using switches 114 and 114’. Using the switches 114 and 114’, a short high voltage pulse is generated. The pulse is transferred to the electrodes 200 and 200’. The pulsed power generator is configured for generating pulses used for breaking the mineral substrate 400, such as nanosecond (ns) pulses to the electrodes 200 and 200’.

[0141] A pair of a first electrode 200 and a second electrode 200’ are arranged at the front end 121 of the drill head 120, protruding slightly therefrom.

[0142] The first electrode 200 comprises a solid electrode portion (not shown) arranged at a front end of the electrode 200. The solid electrode portion may be made at least partially of electrically conductive material and may be either metallic or ceramic.

[0143] The solid electrode portions of the first and second electrodes 200, 200’ are galvanically connectable to the pulsed power generator 110 by means of switches 114, 114’. This is achieved by galvanically connecting the solid electrode portion of the first electrode 200 to the switch 114, so that a high voltage current pulse 150 generated by the pulsed power generator 110 passes to the solid electrode portion of the first electrode 200, where a discharge is formed between the solid electrode portion 201 and the mineral substrate 400 through the first fluid volume 210. As the switches 114, 114’ are closed, the high voltage current pulse 150 thus passes between the solid electrode portion of the first electrode 200 and the solid electrode portion of the second electrode 200’ via the first fluid volume 210, the mineral substrate 400, and the second fluid volume 210’. As a result, a channel is formed in the mineral substrate 400 and the mineral substrate 400 is broken.

[0144] The example embodiment of a pulsed power drilling system 100 illustrated in Fig. 1 further comprises a fluid supply system 140 for supplying a shielding fluid, such as a flushing fluid, e.g., water, to a region between the drill head 120 and the mineral substrate 400 via a fluid conduit 141 having an outlet 142 located between the first and the second electrodes 200, 200’. The flushing fluid isolates the first fluid volume 210 from the second fluid volume 210’. The same pulsed power drilling system 100 may be configured to use a combination of electrodes arranged around a perimeter of the drill head 120 and the outlet 142 of the shielding fluid conduit 141 may then by way of example be positioned at a center of the drill head 120, but a variety of different configurations are possible.

[0145] Fig. 2 schematically illustrates an embodiment of a pulsed power drilling system 100 configured for passing a pulsed electrical current through a mineral substrate 400 to break it. The pulsed power drilling system 100 in the embodiment shown in Fig. 2 comprises a pulsed power drilling tool 101, which is schematically represented in Fig. 2 by a pulsed power generator 110 including a pulse transformer 112 in the form of a bank of capacitors and two electrodes 200, 200’, and an arrangement for generating micro wave radiation 180. The pulsed power drilling tool schematically represented in Fig. 2 may typically further comprise at least the pulsed power generator 110, the power supply 113, the transformer 111 and the switches 114 and 114’ (not shown in Fig. 2) of the pulsed power drilling system 100 illustrated in Fig. 1 and described above.

[0146] The arrangement for generating microwave radiation 180 in the embodiment illustrated in FIG. 2 comprises a microwave generator 181 which is physically separated from the pulsed power drilling tool 101. The microwave generator 181 generates microwave radiation that is emitted in the fluid volume 210 extending from the solid electrode portion of a first electrode 200 of the pulsed power drilling tool 101 to a surface of the mineral substrate 400.

[0147] The arrangement for generating microwave radiation 180 illustrated in FIG. 2 comprises a microwave generator including a circuit for generating microwave radiation 182. The circuit 182 is connected to a waveguide 183 configured to transport the microwave radiation generated by the circuit 182 in the direction of the fluid volume 210. The example embodiment of an arrangement for generating microwave radiation 180 shown in FIG. 2 further comprises a microwave- transmissive device 184 configured for positioning the focus point of the microwave radiation so that the focus point of the microwave radiation is in the fluid volume 210 extending between the solid electrode portion of the first electrode 200 and the surface of the mineral substrate 400. The microwave radiation generated by the circuit 182 of the microwave generator 181 is thereby emitted in the fluid volume 210 extending from the solid electrode portion of the first electrode 200 to a surface of the mineral substrate 400. The solid electrode portions of the first and second electrodes 200, 200’ are configured to be connected to the pulsed power generator 110. In the embodiment shown in Fig. 2, the second electrode 200’ is in direct contact with the mineral substrate 400. After at least a portion of the microwave radiation generated by the micro wave generator 181 is transmitted / emitted into the fluid volume 210 extending between the solid electrode portion of the first electrode 200 and the surface of the mineral substrate 400 in order to at least partly ionize the fluid volume 210, a high voltage current pulse 150 passes between the solid electrode portion of the first electrode 200 and the solid electrode portion of the second electrode 200’ via the at least partly ionized fluid volume 210 and the mineral substrate 400. As a result, a channel is formed in the mineral substrate 400 and the mineral substrate 400 is broken.

[0148] Fig. 3 schematically illustrates an embodiment of a pulsed power drilling system 100 configured for passing a pulsed electrical current through a mineral substrate 400 to break it. The pulsed power drilling system in the embodiment shown in Fig. 3 comprises a pulsed power drilling tool 101, which is schematically represented in Fig. 3 by a pulse transformer 112 in the form of a bank of capacitors and two electrodes 200, 200’, and an arrangement for generating microwave radiation 180. The pulsed power drilling tool 101 schematically represented in Fig. 3 may typically further comprises the pulsed power generator 110, the power supply 113, the transformer 111 and the switches 114 and 114’ (not shown in Fig. 3) of the pulsed power drilling system 100 illustrated in Fig. 1 and described above.

[0149] The solid electrode portion of the first electrode 200 in the embodiment shown in Fig. 3 is configured to be electrically connected to the microwave generator 181 of the arrangement for generating micro wave radiation 180. Hence, the solid electrode portion of the first electrode 200 in Fig. 3 is configured to be connected to the pulsed power generator 181 to carry a discharge generated by the pulsed power generator 181 and, in addition, is configured to be connected to the microwave generator 181 to function as an antenna for emitting the micro wave radiation generated by the microwave generator 181 in the fluid volume 210.

[0150] The solid electrode portions of the first and second electrodes 200, 200’ are connectable to the pulsed power generator 110. In the embodiment shown in Fig. 3, the second electrode 200’ is in direct contact with the mineral substrate. After at least a portion of the microwave radiation generated by the microwave generator is transmitted / emitted from the solid electrode portion of the first electrode 200 into the fluid volume extending between the solid electrode portion of the first electrode 200 and the surface of the mineral substrate 400 in order to at least partly ionize the fluid volume 210, a high voltage current pulse 150 passes between the solid electrode portion of the first electrode 200 and the solid electrode portion of the second electrode 200’ via the at least partly ionized fluid volume 210 and the mineral substrate 400. As a result, a channel is formed in the mineral substrate 400 and the mineral substrate 400 is broken. Typically, at least one switch (not shown), is used for connecting the solid electrode portion of the first electrode 200 to the pulsed power generator so that the solid electrode portion of the first electrode 200 is not concurrently connected to the micro wave generator 181 and the pulsed power generator 110.

[0151] Fig. 4 schematically illustrates an embodiment of a pulsed power drilling system 100 configured for passing a pulsed electrical current through a mineral substrate 400 to break it. The pulsed power drilling system in the embodiment shown in Fig. 4 comprises a pulsed power drilling tool 101, which is schematically represented in Fig. 4 by a pulse transformer 112 in the form of a bank of capacitors and two electrodes 200, 200’, and an arrangement for generating microwave radiation 180 comprising a microwave generator 181 and an aperture 185 configured to position the focus point of microwave radiation.

[0152] In the embodiment illustrated in Fig. 4, at least a portion or part of the aperture 185 is configured to function as the solid electrode portion of the first electrode 200 of the pulsed power drilling tool. The at least portion or part of the aperture 185 functioning as the solid electrode portion of the first electrode 200 is configured to be connected to the pulsed power generator 110 to carry a discharge generated by the pulsed power generator 110. The aperture 185 is further configured to be used for positioning the focus point of the microwave radiation generated by the microwave generator 110 so that the focus point of the microwave radiation is in the fluid volume 210 extending between the aperture 185 / solid electrode portion of the first electrode 200 and the surface of the mineral substrate 400.

[0153] Hence, the aperture 185 in Fig. 4 is configured to be connected to the pulsed power generator 110 to carry a discharge generated by the pulsed power generator 110 and, in addition, is configured to be connected to the microwave generator 181 to function as a focusing means for positioning the focus point of the microwave radiation generated by the microwave generator 110. In the embodiment shown in Fig. 4, the second electrode 200’ is in direct contact with the mineral substrate. The microwave radiation generated by the microwave generator is transmitted through the aperture 185 into the fluid volume 210 extending between the aperture 185 functioning as the solid electrode portion of the first electrode 200 and the surface of the mineral substrate 400 in order to at least partly ionize the fluid volume 210. A high voltage current pulse 150 is then allowed to pass between the aperture 185 functioning as the solid electrode portion of the first electrode 200 and the solid electrode portion of the second electrode 200’ via the at least partly ionized fluid volume 210 and the mineral substrate 400. As a result, a channel is formed in the mineral substrate 400 and the mineral substrate 400 is broken. At least one switch (not shown) is used for connecting the aperture 185 that functions as the solid electrode portion of the first electrode 200 to the pulsed power generator 110 so that the at least portion of the aperture 185 is not concurrently connected to both the microwave generator 181 and the pulsed power generator 110.

[0154] Fig. 5 schematically illustrates an embodiment of a pulsed power drilling system 100 configured for passing a pulsed electrical current through a mineral substrate 400 to break it. The pulsed power drilling system in the embodiment shown in Fig. 5 comprises a pulsed power drilling tool 101, which is schematically represented in Fig. 4 by a pulse transformer 112 in the form of a bank of capacitors and two electrodes, and an arrangement for generating microwave radiation 180 comprising a micro wave generator 181 comprising a circuit for generating micro wave radiation 182, a waveguide 183 for transporting the micro wave radiation generated by the microwave generator 181 and a microwave-transmissive device 184 including lenses configured for positioning the focus point of the microwave radiation generated by the microwave generator 180.

[0155] The arrangement for generating microwave radiation in Fig. 5 includes a casing 186 which constitutes portions of the waveguide 183 and within which the microwave- transmissive device 184 and at least portions of the micro wave generator 181 is contained. In the embodiment shown in Fig. 5, the casing 186 including part of the structure of the waveguide 183 and part of the structure of the microwave- transmissive device 184, is configured to function as the solid electrode portion of the first electrode 200 in that the casing 186 is configured to be connected to the pulsed power generator 110. Fig. 6 illustrates schematically illustrates an embodiment of a pulsed power drilling system 100 configured for passing a pulsed electrical current through a mineral substrate 400 to break it. The pulsed power drilling system illustrated in Fig. 6 corresponds to the pulsed power drilling system illustrated in Fig. 1 with the difference that the solid electrode portions of the respective of the two electrodes 200, 200’ in Fig. 1 are replaced by the structure, or casing 186, of the respective arrangement for generating microwave radiation 180, 180’. The respective arrangement for generating microwave radiation 180, 180’ in Fig. 6 each comprises a microwave generator 181, 181’ in the form of a solid-state microwave generator. The casing 186 of the respective arrangement for generating microwave radiation 180, 180’ functioning as the respective solid electrode portions of the respective of the two electrodes 200, 200’ are configured to be connected to their respective micro wave generator 181, 181’.

[0156] The drill head 120 in FIG. 1 may further comprise one or more contact members (not shown) protruding in the axial direction of the drilling tool 100 with respect to at least the solid electrode portion of the first electrode, i.e., from the front end 121 of the drill head 120. In addition, or alternatively, the pulsed power drilling tool 100 may comprise a positioning device (not shown) for controlling a distance between at least the first solid electrode portion 201 and the surface of the mineral substrate 400.

[0157] The pulsed power drilling tool may further comprise an electronic control unit 160 for controlling operation of the pulsed power drilling system 100 in response to signals received from an external control unit 170, such as a control unit of a machine, e.g. drill rig, in which the pulsed power drilling system is provided. The electronic control unit 160 may include a microprocessor, a microcontroller, a programmable digital signal processor or another programmable device. Thus, the control unit 160 comprises electronic circuits and connections (not shown) as well as processing circuitry (not shown) for communicating with different parts of the drilling tool 100 as well as with the external control unit 170. For example, the control unit 160 may be configured for communicating with various sensors, devices, systems and control units of the drilling tool 100. In the shown embodiment, the control unit 160 controls the transformer 111 as well as the switches 114, 114’. The electronic control unit 160 may comprise modules in either hardware or software, or partially in hardware or software, and communicate using known transmission buses such a CAN-bus and / or wireless communication capabilities. The processing circuitry may be a general-purpose processor or a specific processor. The control unit 160 may comprise a non-transitory memory for storing computer program code and data. Thus, the skilled person realizes that the electronic control unit 160 may be embodied by many different constructions.

[0158] The technology disclosed further relates to the use of a pulsed power drilling system according to any of the embodiments of a pulsed power drilling system shown in Figs. 1 to 6 for breaking of a mineral substrate, such as in any one of rock drilling, concrete processing, mineral processing, and continuous mining.

[0159] An example method for breaking a mineral substrate by passing a pulsed electrical current through the mineral substrate by means of any of embodiments of a pulsed power drilling system is illustrated in Fig. 7. The method comprises the following actions / steps:

[0160] 710: Position drill head, i.e. positioning the drill head so that the plurality of solid electrode portions are at least in proximity of a surface of the mineral substrate;

[0161] 720: Generate microwave (MW) radiation, i.e. generating, by use of an arrangement for generating microwave radiation, microwave radiation used for at least partly and temporarily ionizing a fluid volume extending from a solid electrode portion of a first electrode to a surface of the mineral substrate;

[0162] 730: Emit microwave (MW) into fluid volume, i.e. emitting the generated micro wave radiation in the fluid volume.

[0163] 740: Generate high voltage (HV) current pulse, i.e. generating, by use of a pulsed power generator, a high voltage current pulse; and

[0164] 750: Pass pulse between electrodes, i.e. passing the high voltage current pulse between said electrode portion of a first electrode and a solid electrode portion of a second electrode of the drill head via the at least partly ionized fluid volume and the mineral substrate. In example embodiments, the method according to the technology disclosed comprises the following actions / steps: positioning the drill head 120 so that the solid electrode portions of the plurality of electrodes 200, 200’ are at least in proximity of a surface of the mineral substrate 400; generating, by an arrangement for generating microwave radiation 180, microwave radiation adapted to be used for at least partly and temporarily ionizing a fluid volume 210; transmitting the generated microwave radiation in the fluid volume 210 extending from a solid electrode portion of a first electrode 200 of the drill head 120 of the pulsed power drilling system 100 to a surface of the mineral substrate 400; and generating, by a pulsed power generator 110, a high voltage current pulse 150 that is allowed to pass from the solid electrode portion of the first electrode 200 to a solid electrode portion of a second electrode 200’ via the at least partly ionized fluid volume 210 and the mineral substrate 400.

[0165] The method may also comprise an optional step of emitting the microwave radiation generated by the microwave generator from a solid electrode portion of the first electrode functioning as a microwave antenna supplying shielding fluid to a region between the electrodes 200, 200’ at least during the action of passing the high voltage current pulse from the first electrode 200 to the second electrode 200’. Shielding fluid is preferably continuously supplied.

[0166] Fig. 8 illustrates schematically a drill rig 500, or rock drilling machine, comprising a drilling system 100 as shown in any of Figs. 1 to 6, drilling a hole 401 in a mineral substrate 400 in the form of a rock. The drill rig 500 comprises the alternating current (AC) power supply 113 for powering the pulsed power generator 110. It further comprises the compressed gas supply system 130 and the fluid supply system 140. A hydraulic, pneumatic, or electrically actuated arm 510 for at least vertical positioning of the drilling tool 100 is provided, such as in response to signals from one or more position sensors (not shown) or similar sensing the distance between the electrodes and the mineral substrate surface. The drill rig 500 further comprises ground engaging members 520 for moving the drill rig 500 in a direction parallel with the rock 400.

[0167] It is to be understood that the present disclosure is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Claims

CLAIMS1. A pulsed power drilling system ( 100) configured for passing a pulsed electrical current (150) through a mineral substrate (400) to break the mineral substrate (400), the pulsed power drilling system (100) comprising:- a pulsed power generator (110) for generating high voltage current pulses (150),- a drill head (120) comprising a plurality of electrodes (200, 200’) comprising a solid electrode portion configured to be connected to the pulsed power generator (110), and- an arrangement for generating microwave radiation (180) used for at least partly and temporarily ionizing a fluid volume (210) extending from a solid electrode portion of a first electrode (200) to a surface of the mineral substrate (400), so as to allow a high voltage current pulse (150) generated by the pulsed power generator (110) to pass between said solid electrode portion of a first electrode (200) and a solid electrode portion of a second electrode (200’) of the drill head (120) via the at least partly ionized fluid volume (210) and the mineral substrate (400).

2. The pulsed power drilling system according to claim 1, wherein the arrangement for generating microwave radiation comprises a microwave generator including a circuit for generating microwave radiation, and wherein said circuit is connected to a waveguide configured to transport the microwave radiation generated by the circuit in the direction of the fluid volume so as to allow the generated microwave radiation to be emitted in the fluid volume extending from the solid electrode portion of the first electrode to a surface of the mineral substrate.

3. The pulsed power drilling system according to any of claims 1 and 2, wherein the pulsed power drilling system further comprises at least one microwave- transmissive device configured for positioning the focus point of the microwave radiation so that the focus point of the microwave radiation is in the fluid volume extending between the solid electrode portion of the first electrode and the surface of the mineral substrate.

4. The pulsed power drilling system according to claim 4, wherein the at least one microwave-transmissive device for positioning the focus point of the emitted microwave radiation comprises at least one lens.

5. The pulsed power drilling system according to any of claims 1 to 4, wherein said arrangement for generating microwave radiation is comprising at least one microwave generator in the form of at least one of a magnetron, a solid- state microwave generator, a maser, travelling wave tubes and frequency multipliers.

6. The pulsed power drilling system according to any of claims 1 to 5, wherein said pulsed power drilling system comprises a pulsed power drilling tool including said pulsed power generator and said drill head, and wherein said arrangement for generating microwave radiation comprises a microwave generator separated from the pulsed power drilling tool and configured to emit microwave radiation in the fluid volume extending from the solid electrode portion of the first electrode to a surface of the mineral substrate.

7. The pulsed power drilling system according to any of claims 1 and 4, wherein said first solid electrode portion is configured to be electrically connected to a micro wave generator of the arrangement for generating micro wave radiation, and wherein at least said solid electrode portion of the first electrode among said plurality of solid electrode portions is further configured to also function as an antenna for emitting the microwave radiation generated by the microwave generator.

8. The pulsed power drilling system according to claim 7, wherein at least said solid electrode portion of the first electrode among said plurality of solid electrode portions is further configured to also function as a waveguide for transporting the microwave radiation generated by the microwave generator to the fluid volume extending from the solid electrode portion of the first electrode to a surface of the mineral substrate.

9. The pulsed power drilling system according to any of claims 7 and 8, wherein arrangement for generating microwave radiation comprises at least one microwave generator, and wherein at least said solid electrode portion of thefirst electrode among said plurality of solid electrode portions is configured to be electrically connected to at least one of the at least one microwave generator in the form of at least one of a magnetron, a solid-state generator, a maser, travelling wave tubes and frequency multipliers.

10. The pulsed power drilling system according to claim 9, wherein the microwave generator comprises a circuit for generating microwave radiation and said circuit is configured to be electrically connected to a waveguide configured to transport the microwave radiation generated by the circuit in the direction of at least said solid electrode portion of the first electrode functioning as a micro wave antenna for emitting the microwave radiation.

11. The pulsed power drilling system according to claim 10, wherein the waveguide is a dielectrically filled waveguide configured to transport the microwave radiation from the circuit for generating microwave radiation to said solid electrode portion of the first electrode.

12. The pulsed power drilling system according to any of claims 7 to 11, wherein the pulsed power drilling system further comprises at least one microwave- transmissive device for positioning the focus point of the microwave radiation emitted from said solid electrode portion of the first electrode functioning as an antenna so that the focus point is between said solid electrode portion of the first electrode and the surface of the mineral substrate.

13. The pulsed power drilling system according to claim 12, wherein the at least one microwave-transmissive device for positioning the focus point of the microwave radiation comprises at least one lens.

14. A method for breaking a mineral substrate by passing a pulsed electrical current through the mineral substrate by use of a pulsed power drilling system comprising a pulsed power generator and a drill head comprising a plurality of electrodes comprising a solid electrode portion configured to be connected to the pulsed power generator, the method comprising:- positioning (710) the drill head so that the plurality of solid electrode portions are at least in proximity of a surface of the mineral substrate;- generating (720), by use of an arrangement for generating microwave radiation, microwave radiation used for at least partly and temporarily ionizing a fluid volume extending from a solid electrode portion of a first electrode to a surface of the mineral substrate;- emitting (730) the generated microwave radiation in the fluid volume;- generating (740), by use of a pulsed power generator, a high voltage current pulse; and- passing (750) the high voltage current pulse between said electrode portion of a first electrode and a solid electrode portion of a second electrode of the drill head via the at least partly ionized fluid volume and the mineral substrate.

15. The method according to claim 14, wherein the pulsed power drilling system further comprises at least one microwave-transmissive device for positioning the focus point of microwave radiation, said method further comprising:- positioning, by use of said at least one microwave-transmissive device, the focus point of the microwave radiation so that the focus point is between said solid electrode portion of said first electrode and the surface of the mineral substrate.

16. The method according to any of claims 14 and 15, wherein said arrangement for generating microwave radiation includes a microwave generator comprising a circuit for generating microwave radiation and a waveguide, and wherein said circuit is electrically connected to the waveguide, said method further comprising:- transporting, through said waveguide, the micro wave radiation generated by the circuit in the direction of said solid electrode portion of said first electrode.

17. The method according to any of claims 14 to 16, wherein said arrangement for generating microwave radiation includes a microwave generator comprising a circuit for generating microwave radiation and at least said solid electrode portion of said first electrode among said plurality of solid electrode portions is electrically connected to said circuit of the microwave generator and configured to also function as an antenna, said step of emitting microwave radiation is comprising:- emitting the microwave radiation generated by said circuit of the microwave generator from at least said solid electrode portion of the first electrode functioning as a microwave antenna.

18. The method according to any of claims 14 to 17, wherein said arrangement for generating microwave radiation includes a microwave generator comprising a circuit for generating microwave radiation, and wherein at least said first solid electrode portion among said plurality of solid electrode portions is electrically connected to said circuit of the microwave generator and is further configured to also function as a waveguide for transporting the microwave radiation generated by the circuit of the microwave generator, said method further comprising:- transporting the generated microwave radiation via said solid electrode portion of the first electrode so that the microwave radiation is emitted in the fluid volume extending from said solid electrode portion of the first electrode to a surface of the mineral substrate.

19. A drill rig (500) comprising a pulsed power drilling system (100) according to any one of claims 1- 13 for breaking of a mineral substrate (400), such as in any one of rock drilling, concrete processing, mineral processing, and continuous mining.

20. Use of a pulsed power drilling system according to any one of claims 1-13 for breaking of a mineral substrate, such as in any one of rock drilling, concrete processing, mineral processing, and continuous mining.

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