A drilling equipment and a method of operation

Abstract

The present disclosure relates to a method of operating a pulsed power drilling equipment (100) comprising a drill head (101), a liquid supply system (110), and a liquid retrieval system (120), the method comprising: - controlling the drill head to drill a hole (2) in a mineral substrate (1) in a drilling operation by passing a high voltage current pulse (5) through the mineral substrate, - controlling the liquid supply system to supply a liquid (3) to the hole during the drilling operation, - controlling the liquid retrieval system to retrieve the liquid from the hole during the drilling operation, wherein the liquid supply system and the liquid retrieval system are controlled such that a level (4) of the liquid within the hole is at a target level (h) set such that an upper portion (2a) of the drilled hole is free from the supplied liquid.

Description

[0001] A DRILLING EQUIPMENT AND A METHOD OF OPERATION

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to rock drilling and handling of fluid during rock drilling. In certain aspects, it relates to a method of operating a drilling equipment. The disclosure further relates to a drilling equipment and a drill rig.

[0004] BACKGROUND

[0005] During rock drilling it is often necessary to supply a fluid towards the mineral substrate to be drilled. The fluid is sometimes referred to as a flushing fluid, and one of its functions is to remove rock debris from the drilled hole. In surface drilling operations, the fluid generally consists of a gas, such as compressed air. By flushing the hole with compressed air, rock debris is efficiently flushed out of the hole. Compressed air can easily be provided by means of a compressor.

[0006] In underground drilling applications, a liquid instead of a gas is often used as the flushing fluid. The liquid, which may be oil or water, may in those cases be continuously pumped or ejected into the hole at high pressure, whereafter it is guided up from the hole via an annular cavity formed between a wall of the drilled hole and the drilling equipment used for drilling the hole. Liquid flushing is generally more energy efficient than compressed air and can hence contribute to lowering energy consumption at the drilling site. However, water or oil is usually a limited resource at the drilling site, and it is therefore generally desired to collect the used liquid and recirculate it into the hole.

[0007] A problem that may arise when a liquid is used as the flushing fluid is that the liquid may diffuse into cracks extending from the drilled hole before it reaches the ground surface above the hole. This prevents efficient recirculation of the flushing fluid, which may be particularly problematic in regions without natural sources of liquid. SUMMARY

[0008] A primary object of the present disclosure is to achieve an in at least some aspect improved method of operating a drilling equipment and an in at least some aspect improved drilling equipment. In particular, it is an object to achieve a method and a drilling equipment which facilitate the use of a liquid as a flushing fluid, also in surface drilling operations.

[0009] According to a first aspect of the disclosure, a method of operating a drilling equipment according to claim 1 is provided. The drilling equipment comprises a drill head having at least two electrodes, a pulsed power generator for generating high voltage current pulses, a liquid supply system, and a liquid retrieval system. The method comprises: controlling the drill head to drill a hole in a mineral substrate in a drilling operation by passing a high voltage current pulse generated by the pulsed power generator between the at least two electrodes via the mineral substrate, controlling the liquid supply system to supply a liquid to the hole during the drilling operation, and controlling the liquid retrieval system to retrieve the liquid from the hole during the drilling operation.

[0010] The liquid supply system and the liquid retrieval system are controlled such that a level of the liquid within the hole is at a target level or within a target range during the drilling operation, the target level or target range being set such that an upper portion of the drilled hole is free from the supplied liquid.

[0011] By the proposed method, it is possible to concentrate the liquid to a lower portion of the hole, where the drill head is located, while the upper portion is kept dry during the drilling operation. This means that seepage, or leakage through cracks in a wall of the hole, can be reduced thanks to the smaller portion of the hole being exposed to the liquid. An improved recirculation of the liquid can hence be achieved. In this way, advantages associated with using a liquid flushing fluid instead of a gaseous flushing fluid such as compressed air can be achieved even when the supply of liquid, such as water, oil, or emulsion, is limited. Such advantages may include reduced energy consumption, less dust, and a better stability of the drilled hole. The method may in some embodiments be carried out at least in part by an electronic control unit comprising processing circuitry. In some embodiments, the method may at least in part be carried out by a control system comprising switches configured to automatically switch the liquid supply system and the liquid retrieval system on and off in dependence on the level of the liquid within the hole.

[0012] The target level or target range may be measured from a bottom of the drilled hole. The drilled hole may extend downward, such as in a vertical direction or in a slanted direction. The upper portion of the hole is to be understood as the portion of the hole which is closest to a surface of the mineral substrate in which the hole is formed, i.e., the surface relative to which the hole is defined.

[0013] Optionally, the liquid supply system comprises a liquid supplying pump, and controlling the liquid supply system such that the level of the liquid within the hole is at the target level or within the target range comprises controlling a flow rate of the liquid supplying pump. The liquid supply system may further comprise at least one liquid supply conduit having an outlet at the drill head, such that the liquid can be provided to a location near the electrodes of the drill head.

[0014] Optionally, the liquid retrieval system comprises a liquid retrieving pump, and controlling the liquid retrieval system such that the level of the liquid within the hole is at the target level or within the target range comprises controlling a flow rate of the liquid retrieving pump. The liquid retrieval system may further comprise at least one liquid retrieval conduit having an inlet at the drill head, such that liquid can be sucked into the inlet close to the bottom of the hole.

[0015] Optionally, the method may comprise controlling the flow rates of the liquid retrieving pump and the liquid supplying pump to predetermined target flow rates. In this way, when the dimension of the hole is known, the level of the liquid can be controlled with reasonable accuracy to be within the target range, without relying on sensors or switches detecting the level of the liquid.

[0016] Optionally, the drilling equipment further comprises at least one sensor or switch arranged to detect the level of the liquid within the hole, wherein the method comprises: detecting the level of the liquid using the at least one sensor or switch, wherein at least one of the liquid supply system and the liquid retrieval system is controlled in dependence on the detected level of the liquid. In some embodiments, the liquid supply system and the liquid retrieval system are controlled to supply and retrieve the liquid, respectively, in dependence on the detected level of the liquid. The use of a sensor or switch detecting the liquid level ensures that the target level or range is not violated, e.g., if leakage occurs. The at least one sensor or switch may comprise at least one of a float sensor, a pressure sensor, and a level switch. In some embodiments, the sensor may collect measurement data that may be used to determine the level of the liquid, such as pressure data, which are communicated to an electronic control unit controlling the liquid supply system and / or the liquid retrieval system, to achieve a precise control of the level of the liquid. In other embodiments, a simplified control of the level may be achieved by turning pump(s) or similar on and off in response to signals from one or more switches, such as level switches.

[0017] Optionally, the method further comprises varying the target value or target range during the drilling operation. This allows controlled adjustment of the level of the liquid during drilling. A pressure sensor may be used to enable such an adjustment.

[0018] Optionally, the method further comprises: detecting at least one crack within a wall of the hole, and in response to determining that the at least one crack affects the level of the liquid within the hole, adjusting the target value or target range.

[0019] Hence, the level of the liquid can be controlled to be below the detected at least one crack. In this way, leakage via the crack(s) can be prevented.

[0020] Optionally, the target level or target range is set such that said upper portion of the hole being free from the supplied liquid is a major portion of the hole. By a major portion is herein intended at least 50%, preferably at least 70%, of a total extension of the hole in a drilling direction. A relative extension of the upper portion of the hole, being free from supplied liquid, may typically increase as the depth of the hole increases, since the target level or target range is measured from the bottom of the drilled hole. Preferably, the target level or target range may be set to be as small as possible without affecting the function of the drill head. Optionally, the drilling equipment further comprises a gas supply system and a plasma generator, wherein controlling the drill head to drill the hole further comprises: controlling the gas supply system to supply compressed gas to the plasma generator, controlling the plasma generator to generate at least one plasma volume extending from at least a first one of the electrodes to a surface of the mineral substrate by ionizing the supplied compressed gas, wherein said pulsed power generator is controlled to pass the high voltage current pulse between the two electrodes via the at least one plasma volume and the mineral substrate. By creating a plasma between at least one of the electrodes and the surface of the mineral substrate, it is possible to break the mineral substrate without physical contact between the electrode and the surface of the mineral substrate. Hence, a good electrical contact may be ensured even if the surface is uneven. 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.

[0021] Optionally, the target value or target range is set to a value or range at which a maximum pressure caused by the liquid within the hole is smaller than a gas pressure of the compressed gas at an electrode outlet. This ensures a gas flow out from the electrode via the electrode outlet. By keeping the level of the liquid sufficiently low such that the gas pressure exceeds the pressure caused by the liquid at a bottom of the hole, it is ensured that the plasma generator can function as intended and generate the at least one plasma volume.

[0022] According to a second aspect of the disclosure, at least the primary object is achieved by a drilling equipment according to claim 10. The drilling equipment comprises: a pulsed power generator configured to generate high voltage current pulses, a drill head comprising at least two electrodes, the drill head being configured to drill a hole in a mineral substrate in a drilling operation by passing a high voltage current pulse generated by the pulsed power generator between the at least two electrodes via the mineral substrate, a liquid supply system configured to supply a liquid to the hole during the drilling operation, a liquid retrieval system configured to retrieve the liquid from the hole during the drilling operation, and a control system configured to control the liquid supply system and the liquid retrieval system such that a level of the liquid within the hole is at a target level or within a target range during the drilling operation, the target level or target range being set such that an upper portion of the drilled hole is free from the supplied liquid.

[0023] By the proposed drilling equipment, it is possible to concentrate the liquid to a lower portion of the hole, where the drill head is located, while the upper portion is kept dry during the drilling operation. As described above in connection with the first aspect, a reduced energy consumption, less dust, and a better stability of the drilled hole may be achieved as compared to a drilling equipment using a gaseous flushing fluid.

[0024] Optionally, the liquid supply system comprises a liquid supplying pump, and / or the liquid retrieval system comprises a liquid retrieving pump.

[0025] Optionally, the liquid supply system comprises at least one liquid supply conduit having an outlet at the drill head, and / or the liquid retrieval system comprises at least one liquid retrieval conduit having an inlet at the drill head. The at least one liquid retrieval conduit should be arranged separately from at least an upper wall portion of the hole, such that the liquid can be passed from the lower portion of the hole without coming into contact with the upper wall portion. Hence, leakage via cracks in the upper wall portion can be prevented. Preferably, also the at least one liquid supply conduit may be arranged separately from at least an upper wall portion of the hole.

[0026] Optionally, the control system comprises at least one sensor or switch arranged to detect the level of the liquid within the hole, wherein the control system is configured to control at least one of the liquid supply system and the liquid retrieval system in dependence on the detected level of the liquid. The at least one sensor or switch may comprise at least one of a float sensor, a pressure sensor, and a level switch.

[0027] Optionally, the drilling equipment further comprises a plasma generator configured to generate at least one plasma volume extending from at least a first one of the electrodes to a surface of the mineral substrate by ionizing a compressed gas, and a gas supply system configured to supply the compressed gas to the plasma generator, wherein said pulsed power generator is configured to pass a high voltage current pulse between the two electrodes via the at least one plasma volume and the mineral substrate to break the mineral substrate.

[0028] The drilling equipment according to the second aspect may be configured to perform the method according to any one of the embodiments of the first aspect. Thus, further advantages and advantageous features of the drilling equipment appear from the above description of the method.

[0029] According to a third aspect of the disclosure, a drill rig comprising the drilling equipment according to the second aspect is provided.

[0030] Further advantages and advantageous features of the disclosure are disclosed in the following description and in the dependent claims.

[0031] BRIEF DESCRIPTION OF THE DRAWINGS

[0032] With reference to the appended drawings, below follows a more detailed description of embodiments of the disclosure cited as examples.

[0033] In the drawings:

[0034] Fig. 1 schematically illustrates a drilling equipment according to a first embodiment,

[0035] Fig. 2 schematically illustrates a drilling equipment according to a second embodiment,

[0036] Fig. 3 schematically illustrates a drilling equipment according to a third embodiment,

[0037] Fig. 4 schematically illustrates a drilling equipment according to a fourth embodiment,

[0038] Fig. 5 schematically illustrates a drilling equipment according to a fifth embodiment,

[0039] Fig. 6 schematically illustrates an electrode of a drilling equipment according to an embodiment,

[0040] Fig. 7 is a flow chart illustrating a method according to the disclosure, and Fig. 8 schematically illustrates a drill rig according to an embodiment.

[0041] 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.

[0042] DETAILED DESCRIPTION

[0043] Fig. 1 illustrates schematically a drilling equipment 100 according to a first embodiment. The drilling equipment 100 is a pulsed power drilling equipment comprising a drill head 101 configured to break a mineral substrate 1 in the form of a rock by passing high voltage current pulses 5 through the substrate 1. A pulsed power generator 150 configured to generate high voltage current pulses is provided, and the drill head 101 comprises a number of electrodes, herein two electrodes 102, 103, although a larger number of electrodes may be provided. The electrodes may be identical or non-identical.

[0044] The pulsed power generator 150 comprises a pulse transformer 151 in the form of a bank of capacitors, connected to an electrical power supply 152 via a transformer 153. Electrodes 102, 103 are selected and connected using switches 154 (see Fig. 6), such that a pulse generated by the pulsed power generator 150 is transferred to the electrodes 102, 103. The pulsed power generator 150 is configured for generating pulses used for breaking the mineral substrate 1, such as nanosecond (ns) pulses, when the pulses pass through the mineral substrate 1.

[0045] The mineral substrate 1 comprises an essentially horizontal ground surface 10 in which a drilled hole 2 is formed by the drilling equipment 100. Although the hole 2 is herein illustrated as a vertically extending hole 2 formed at a substantially right angle with respect to a horizontal ground surface 10, it is possible that the hole may extend at another angle, and / or that the ground surface is not a horizontal surface. The hole 2 extends into the mineral substrate 1, the bottom of the hole 2 being defined by a drilled surface 6, whereby the depth of the hole 2 increases as the mineral substrate 1 is broken by the drill head 101 at the drilled surface 6. The hole 2 may have a circular cross-section or a square cross-section, or any cross-sectional shape, dependent on how the drill head 101 is configured.

[0046] The drilling equipment further comprises a liquid supply system 110 configured to supply a liquid 3 to the hole 2 during the drilling operation, such as water, emulsion, or oil. The liquid 3 may contain impurities. For example, when water is used as the liquid 3, it may be saline water. The liquid supply system 110 comprises a reservoir 112 to which a liquid supply conduit 113 is fluidly connected. The reservoir 112 is located outside of the drilled hole 2, such as on a drill rig or on the ground surface 10. The liquid supply conduit 113 has an outlet 114 located near a front end 105 of the drill head 101. A liquid supplying pump 111 is further provided, the liquid supplying pump 111 being arranged to pump liquid 3 from the reservoir 112, via the liquid supply conduit 113, through the outlet 114 and into the hole 2. In the illustrated first embodiment, the liquid supplying pump 111 is located above the ground surface 10.

[0047] The drilling equipment 100 further comprises a liquid retrieval system 120 configured to retrieve the liquid 3 from the hole 2 during the drilling operation and return it to the reservoir 112. A liquid retrieval conduit 123 is provided, having an inlet 124 located at the front end 105 of the drill head 101 , between the electrodes 102, 103. A liquid retrieving pump 121 is further provided, the liquid retrieving pump 121 being a submersible pump arranged to pump liquid 3 from the hole 2, via the inlet 124 and the liquid retrieval conduit 123 and into the reservoir 112. The liquid retrieving pump 121 is herein illustrated as provided within a housing of the drill head 101, although in other embodiments the liquid retrieving pump 121 may be provided outside of such a housing.

[0048] The drilling equipment may also comprise an equipment configured to separate solids from the liquid 3 retrieved from the hole 2. For example, the reservoir 112 may comprise separation means, such as filters, shale shakers, centrifuges, or cyclone separators, or the like, or combinations thereof, for removing rock fragments from the liquid. The reservoir 112 may contain a plurality of separation stages, such that rock fragments comprising different materials, grain sizes, or the like may be removed, for example having a coarse grain separation stage followed by a fine grain separation stage.

[0049] The drilling equipment 100 also comprises a control system configured to control the liquid supply system 110 and the liquid retrieval system 120 such that a level 4 of the liquid 3 within the hole 2 is at a target level h, or within a target range (not shown in Fig. 1) during the drilling operation. The target level h is set such that an upper portion 2a of the drilled hole 2 is free from the supplied liquid 3. The upper portion 2a is herein to be understood as the portion of the hole 2 which is closest to the ground surface 10, regardless of the direction of the hole 2. In other words, the liquid 3 is only located close to a bottom of the hole 2. A major portion of the hole 2 may be free from liquid. The liquid retrieving pump 121 is in the first embodiment located below the target level h, i.e. , the liquid retrieving pump 121 is submersed into the liquid 3 provided within a lower portion of the hole 2.

[0050] The control system herein comprises an electronic control unit 140 configured to control operation of the drilling equipment 100. A sensor 130 in the form of a pressure sensor is arranged to measure the pressure at the front end 105 of the drill head. The pressure will depend on the level 4 of the liquid 3 within the hole 2. Measurement data relating to the pressure may be communicated from the sensor 130 to the electronic control unit 140, which in turn controls, e.g., flow rates of the liquid supplying pump 111 and the liquid retrieving pump 121.

[0051] The sensor 130 may comprise a pressure transducer. Alternatively, the sensor 28 may comprise an ultrasonic, optical, capacitance, or radar-based sensor, a float switch, or any known sensor for determining a liquid level. The sensor 130 may be attached on the drill head 101 , or alternatively it may extend from an external surface of the drill head 101. Alternatively, the sensor 130 may be located elsewhere on the drilling equipment 100, as long as it is able to collect measurement data indicative of the level 4 of the liquid 3 within the hole 2.

[0052] Fig. 2 illustrates a drilling equipment 100 according to a second embodiment, which differs from the first embodiment in the placement of the outlet 114 of the liquid supply system 110 and the inlet 124 of the liquid retrieval system 120. The inlet 124 is herein located at the front end 105 of the drill head 101 , closer to a peripheral wall of the drill head 101 , while the outlet 114 is located at the front end 105 between the electrodes 102, 103.

[0053] Fig. 3 illustrates a drilling equipment 100 according to a third embodiment, which differs from the second embodiment in that the liquid retrieving pump 121 is located above the ground surface 10. To provide sufficient pressure at the inlet 124, a pressurizing system is provided, comprising a compressor 160 and a sealing member 161. The sealing member 161 seals the hole 2 against the drill head 101 close to a rear end 106 of the drill head 101 , the rear end 106 being opposite to the front end 105. The compressor 160 is arranged to provide compressed air into the hole 2 via a valve or inlet in the sealing member 161, thereby pressurizing the hole 2 to achieve a pressure above atmospheric pressure. With the increased pressure, the liquid retrieving pump 121 is able to pump the liquid 3 out from the hole 2 even when provided outside of the hole 2.

[0054] Fig. 4 illustrates a drilling equipment 100 according to a fourth embodiment. The drilling equipment 100 herein comprises a submersible liquid retrieving pump 121 and the placement of the inlet 124 of the liquid retrieval system 120 and the outlet 114 of the liquid supply system 110 is the same as in the second embodiment. The drilling equipment 100 according to the fourth embodiment differs from the second embodiment in that, instead of a pressure sensor, first and second level switches 131, 132, also referred to as float switches, are provided. The level switches 131, 132 together define a target range h1-h2, as measured from the drilled surface 6, within which the level 4 of the liquid 3 may vary. A control unit 133 is configured to control the liquid retrieving pump 121 in dependence on signals received from the level switches 131, 132 such that the level 4 of the liquid is within the target range h1-h2. Although not illustrated, the liquid supply pump 111 may also be controlled in dependence on the signals received from the level switches 131, 132. Alternatively, the liquid supply pump 111 may be configured to supply the liquid 3 at a fixed flow rate, while the liquid retrieving pump 121 is used to control the level 4 of the liquid 3.

[0055] Fig. 5 illustrates a drilling equipment 100 according to a fifth embodiment, which differs from the previous embodiments in that no pressure sensor 130 or level switches 131, 132 are provided. Instead, the liquid retrieval conduit 123 is positioned with its inlet 124 located at the target level h, i.e. , at a distance from the electrodes 102, 103 corresponding to the target level h. The liquid retrieving pump 121 is illustrated as provided within the drill head 101 , but above the target level h. The liquid retrieving pump 121 may herein be a pump that can run dry without being damaged, such that it can be active during the entire drilling operation and remove liquid whenever the level 4 of the liquid 3 increases above the target level h. The flow rate of the liquid retrieving pump 121 may hence be set to be at least equal to the flow rate of the liquid supplying pump 111 , which may be set to supply liquid at a constant flow rate.

[0056] Fig. 6 illustrates an electrode 102’, which may in some embodiments be used as at least a first one of the electrodes 102, 103 of the drilling equipment 100 illustrated in Figs. 1-5.

[0057] The electrode 102’ comprises a hollow solid electrode portion 601 arranged at a front end of the electrode 102’. The solid electrode portion 601 is herein shown to be screwmounted and thereby replaceable. It is made at least partially of electrically conductive material and may be either metallic or ceramic. At least a part must be heat resistant and capable to carry the plasma return current. By way of example, the solid electrode portion 601 may be made of tungsten, stainless steel, aluminum, copper, or zirconium oxide ceramics. An insulating protective skin 602 is provided on an external surface of the solid electrode portion 601, protecting it from direct contact with an environment surrounding the electrode 102’.

[0058] The first electrode 102’ further comprises a plasma generator 620. The plasma generator

[0059] 620 is configured for generating a plasma volume 610, extending from the electrode 102’ to a surface 1a of the mineral substrate 1. A compressed gas supply system 630 is provided for supplying compressed gas to the plasma generator 620 of the electrode 102’, such as compressed air. The plasma generator 620 ionizes the compressed gas to generate a plasma. This may be carried out using standard procedures.

[0060] In the shown embodiment, the plasma generator 620 uses in the ionization stage a low voltage power source 625, arranged separately from the pulsed power generator 150. The low voltage power source 625 is galvanically connected to on one hand a conductive casing 621 of the plasma generator 620, delimiting a cavity for ionizing the gas, and on the other hand a cone shaped plasmatron electrode 622, spaced apart from the casing

[0061] 621 by a gap that may typically be a few millimeters depending on gas flow.

[0062] The first and second electrodes 102, 103 shown in Fig. 1-5 are galvanically connectable to the electrical power supply 152 by means of switches. In fig. 6, this is illustrated by the switch 154, arranged to galvanically connect the conductive casing 621 and the solid electrode portion 601 to the electrical power supply 152, so that a high voltage current pulse 5 generated by the pulsed power generator 150 passes through the casing 621 and to the solid electrode portion 601, where a discharge is formed between the solid electrode portion 601 and the mineral substrate 1 through the plasma volume 610. The high voltage current pulse 5 may hence pass between the solid electrode portion 601 and the mineral substrate 1.

[0063] The at least two electrodes 102, 103 of the drill head 101 may be identical, but they may also have different configurations. For example, at least a first one 102’ of the electrodes 102, 103 may comprise or be connected to a plasma generator 620, while at least a second one of the electrodes 102, 103 is a solid electrode. In other embodiments, all of the at least two electrodes 102, 103 may be solid electrodes configured to be in physical contact with the surface 1a of the mineral substrate. In yet other embodiments, both electrodes within an electrode pair may be configured to transmit the high voltage current pulse between them via the mineral substrate, without being in physical contact with the mineral substrate.

[0064] A method according to the disclosure, using the drilling equipment 100 as described with reference to Fig. 1-5, will now be described with reference to Fig. 7. The method comprises the following actions S1-S3:

[0065] S1: Controlling the drill head 101 to drill a hole 2 in the mineral substrate 1 in a drilling operation by passing a high voltage current pulse 5 generated by the pulsed power generator 150 between the at least two electrodes 102, 103 via the mineral substrate 1. The mineral substrate is thereby broken.

[0066] S2: Controlling the liquid supply system 110 to supply a liquid 3 to the hole 2 during the drilling operation.

[0067] S3: Controlling the liquid retrieval system 120 to retrieve the liquid 3 from the hole 2 during the drilling operation.

[0068] In the actions S2 and S3, the liquid supply system 110 and the liquid retrieval system are controlled such that a level 4 of the liquid 3 within the hole 2 is at a target level h or within a target range h1-h2 during the drilling operation, the target level h or target range h1-h2 being set such that an upper portion 2a of the drilled hole 2 is free from the supplied liquid 3. The action S2 of controlling the liquid supply system 110 such that the level 4 of the liquid 3 within the hole 2 is at the target level h or within the target range h1-h2 may comprise controlling a flow rate of the liquid supplying pump 111. Similarly, the action S3 of controlling the liquid retrieval system 120 such that the level 4 of the liquid 3 within the hole 2 is at the target level h or within the target range h1-h2 may comprise controlling a flow rate of the liquid retrieving pump 121. In some embodiments, this may be achieved by matching the flow rates of the liquid supplying pump 111 and the liquid retrieving pump 121. In other embodiments, a flow rate of the liquid supplying pump 111 may be set to a fixed flow rate, while the flow rate of the liquid retrieving pump 121 is controlled to vary to keep the liquid 3 at the target level h or within the target range h1-h2. In yet other embodiments, the flow rate of the liquid retrieving pump 121 may be set to a fixed flow rate, while the flow rate of the liquid supplying pump 111 may be varied. Furthermore, in some embodiments, both the flow rate of the liquid supplying pump 111 and the liquid retrieving pump 121 may be varied.

[0069] When the drilling equipment 100 comprises at least one sensor 130 or switch 131 , 132 arranged to detect the level 4 of the liquid 3 within the hole 2, the method may comprise the action S4 of detecting the level 4 of the liquid 3 using the at least one sensor 130 or switch 131, 132. In this case, in the actions S2 and S3, respectively, the liquid supply system 110 and / or the liquid retrieval system 120 may be controlled to supply and / or retrieve the liquid 3, in dependence on the detected level 4 of the liquid 3. In some cases, it may be sufficient to control one of the systems 110, 120 in dependence on the detected level 4, while the other one of the systems 110, 120 may be controlled to supply or retrieve fluid at a fixed flow rate. In other cases, both systems 110, 120 may be controlled in dependence on the detected level 4.

[0070] The method may comprise varying the target value h or target range h1-h2 during the drilling operation, such as when a leak is detected or similar.

[0071] The method may further comprise detecting at least one crack 7 within the hole 2. In response to determining that the at least one crack 7 affects the level 4 of the liquid 3 within the hole 2, the method may comprise adjusting the target value h or target range h1-h2, e.g., such that the level 4 or the liquid 3 is located below the at least one crack 7. When the drilling equipment 100 comprises the gas supply system 630 and the plasma generator 620, the action S1 of controlling the drill head 101 to drill the hole 2 may comprise: controlling the gas supply system 630 to supply compressed gas to the plasma generator 620, controlling the plasma generator 630 to generate at least one plasma volume 610 extending from at least a first one 102’ of the electrodes 102, 103 to a surface 1a of the mineral substrate 1 by ionizing the supplied compressed gas.

[0072] The pulsed power generator 150 is in this case controlled to pass the high voltage current pulse 5 between the two electrodes 102, 103 via the at least one plasma volume 610 and the mineral substrate 1. The target value h or target range h1-h2 may in this case be set to a value or range at which a maximum pressure caused by the liquid 3 within the hole 2 is smaller than a gas pressure of the compressed gas at an electrode outlet, such that the plasma generator 620 is able to generate the plasma volume 610 between the solid electrode portion 601 and the surface 1a of the mineral substrate 1 , despite the liquid pressure at the bottom of the hole 2 caused by the liquid 3 in which the electrode 102’ is at least partially submersed.

[0073] Fig. 8 illustrates a mobile drill rig 800 comprising the proposed drilling equipment 100 drilling a hole 2 in a ground surface 10 of a mineral substrate 1 in the form of a rock. The drill rig 800 comprises the electrical power supply 152 for powering the pulsed power generator 150 and, if present, the plasma generator 620. The liquid supply system 110 with the reservoir 112 and the liquid retrieval system 120 are herein illustrated as being located on the drill rig 800, although they may at least in part of course be located elsewhere, such as on a separate unit, such as on a vehicle or on a stationary unit, as long as the liquid supply system 110 can be arranged to supply liquid into the hole 2 and the liquid retrieval system 120 can be arranged to retrieve liquid therefrom. A hydraulic, pneumatic, or electrically actuated arm 810 for at least vertical positioning of the drilling equipment 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 within the hole 2. The mobile drill rig 800 further comprises ground engaging members 820 for moving the drill rig 800 in a direction parallel with the ground surface 10. Of course, although the drill rid 800 is herein illustrated as a mobile drill rig, the drill rig may in other embodiment be a stationary drill rig, or a drill rig of any other type than the one illustrated. It is to be understood that the present invention 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 method of operating a drilling equipment (100) comprising a drill head (101) having at least two electrodes (102, 103), the drilling equipment (100) further comprising a pulsed power generator (150) for generating high voltage current pulses, a liquid supply system (110), and a liquid retrieval system (120), the method comprising: controlling (S1) the drill head to drill a hole (2) in a mineral substrate (1) in a drilling operation by passing a high voltage current pulse (5) generated by the pulsed power generator (150) between the at least two electrodes (102, 103) via the mineral substrate (1), controlling (S2) the liquid supply system (110) to supply a liquid (3) to the hole (2) during the drilling operation, controlling (S3) the liquid retrieval system (120) to retrieve the liquid from the hole (2) during the drilling operation, wherein the liquid supply system (110) and the liquid retrieval system (120) are controlled such that a level (4) of the liquid (3) within the hole (2) is at a target level (h) or within a target range (h1-h2) during the drilling operation, the target level (h) or target range (h1- h2) being set such that an upper portion (2a) of the drilled hole (2) is free from the supplied liquid (3).

2. The method according to claim 1 , wherein the liquid supply system (110) comprises a liquid supplying pump (111), and wherein controlling the liquid supply system (110) such that the level (4) of the liquid within the hole (2) is at the target level or within the target range comprises controlling a flow rate of the liquid supplying pump (111).

3. The method according to claim 1 or 2, wherein the liquid retrieval system (120) comprises a liquid retrieving pump (121), and wherein controlling the liquid retrieval system (120) such that the level (4) of the liquid within the hole (2) is at the target level or within the target range comprises controlling a flow rate of the liquid retrieving pump (121).

4. The method according to any one of the preceding claims, wherein the drilling equipment (100) further comprises at least one sensor (130) or switch (131 , 132) arranged to detect the level (4) of the liquid (3) within the hole (2), and wherein the method comprises:detecting (S4) the level (4) of the liquid using the at least one sensor (130) or switch (131, 132), wherein at least one of the liquid supply system (110) and the liquid retrieval system (120) is controlled in dependence on the detected level (4) of the liquid (3).

5. The method according to any one of the preceding claims, further comprising:- varying the target value (h) or target range (h1-h2) during the drilling operation.

6. The method according to any one of the preceding claims, further comprising: detecting at least one crack (7) within a wall of the hole (2), in response to determining that the at least one crack (7) affects the level (4) of the liquid within the hole (2), adjusting the target value (h) or target range (h1-h2).

7. The method according to any one of the preceding claims, wherein the target value (h) or target range (h1-h2) is set such that said upper portion (2a) of the hole (2) being free from the supplied liquid (3) is a major portion of the hole (2).

8. The method according to any one of the preceding claims, wherein the drilling equipment (100) further comprises a gas supply system (630) and a plasma generator (620), and wherein controlling the drill head (101) to drill the hole (2) further comprises: controlling the gas supply system (630) to supply compressed gas to the plasma generator (620), controlling the plasma generator (620) to generate at least one plasma volume (610) extending from at least a first one (102’) of the electrodes (102, 103) to a surface (1a) of the mineral substrate (1) by ionizing the supplied compressed gas, wherein said pulsed power generator (150) is controlled to pass the high voltage current pulse (5) between the two electrodes (102, 103) via the at least one plasma volume (610) and the mineral substrate (1).

9. The method according to claim 8, wherein target value (h) or target range (hi — h2) is set to a value or range at which a maximum pressure caused by the liquid (3) within the hole (2) is smaller than a gas pressure of the compressed gas at an electrode outlet.

10. A drilling equipment (100) comprising:a pulsed power generator (150) configured to generate high voltage current pulses, a drill head (101) comprising at least two electrodes (102, 103), the drill head (101) being configured to drill a hole (2) in a mineral substrate (1) in a drilling operation by passing a high voltage current pulse (5) generated by the pulsed power generator (150) between the at least two electrodes (102, 103) via the mineral substrate (1), a liquid supply system (110) configured to supply a liquid (3) to the hole (2) during the drilling operation, a liquid retrieval system (120) configured to retrieve the liquid from the hole (2) during the drilling operation, and a control system (140) configured to control the liquid supply system (110) and the liquid retrieval system (120) such that a level (4) of the liquid (3) within the hole (2) is at a target level (h) or within a target range (h1-h2) during the drilling operation, the target value (h) or target range (h1-h2) being set such that an upper portion (2a) of the drilled hole (2) is free from the supplied liquid (3).

11. The drilling equipment according to claim 10, wherein the liquid supply system (110) comprises a liquid supplying pump (111), and / or wherein the liquid retrieval system (120) comprises a liquid retrieving pump (121).

12. The drilling equipment according to claim 10 or 11, wherein the liquid supply system (110) comprises at least one liquid supply conduit (113) having an outlet (114) at the drill head (101), and / or wherein the liquid retrieval system (120) comprises at least one liquid retrieval conduit (123) having an inlet (124) at the drill head (110).

13. The drilling equipment according to any one of claims 10-12, wherein the control system comprises at least one sensor (130) or switch (131, 132) arranged to detect the level (4) of the liquid (3) within the hole (2), and wherein the control system is configured to control at least one of the liquid supply system (110) and the liquid retrieval system (120) in dependence on the detected level (4) of the liquid (3).

14. The drilling equipment according to any one of claims 10-13, further comprising a plasma generator (620) configured to generate at least one plasma volume (610) extending from at least a first one (102’) of the electrodes (102, 103) to a surface (1a) ofthe mineral substrate (1) by ionizing a compressed gas, and a gas supply system (630) configured to supply the compressed gas to the plasma generator (620), and wherein said pulsed power generator (150) is configured to pass a high voltage current pulse (5) between the two electrodes (102, 103) via the at least one plasma volume (610) and the mineral substrate (1) to break the mineral substrate (1).

15. A drill rig (800) comprising the drilling equipment (100) according to any one of claims 10-14.

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