WO2020234202A1 - Tête de forage pour forage électro-pulsé - Google Patents

Tête de forage pour forage électro-pulsé Download PDF

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Publication number
WO2020234202A1
WO2020234202A1 PCT/EP2020/063742 EP2020063742W WO2020234202A1 WO 2020234202 A1 WO2020234202 A1 WO 2020234202A1 EP 2020063742 W EP2020063742 W EP 2020063742W WO 2020234202 A1 WO2020234202 A1 WO 2020234202A1
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WO
WIPO (PCT)
Prior art keywords
drill
drill head
liquid
electrode
voltage
Prior art date
Application number
PCT/EP2020/063742
Other languages
English (en)
Inventor
Dirk FRANSAER
Alain De Keyser
Guido Heremans
Stefan Vandeplas
Original Assignee
Vito Nv
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Vito Nv filed Critical Vito Nv
Priority to CN202080036556.XA priority Critical patent/CN114174630A/zh
Publication of WO2020234202A1 publication Critical patent/WO2020234202A1/fr

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B7/00—Special methods or apparatus for drilling
    • E21B7/14—Drilling by use of heat, e.g. flame drilling
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B10/00—Drill bits
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B7/00—Special methods or apparatus for drilling
    • E21B7/14—Drilling by use of heat, e.g. flame drilling
    • E21B7/15—Drilling by use of heat, e.g. flame drilling of electrically generated heat

Definitions

  • the present invention relates to electro-pulse-boring (EPB). More specifically it relates to a drill head suitable for drilling large-diameter holes, i.e. diameters equal or larger than 40 cm, with EPB.
  • EPB has been proposed as an alternative for rotary drilling of deep holes.
  • the use of a rotary drilling technique is generally limited for holes up to a depth of about 5 km, whereas EPB can be applied going from shallow depth drilling to deep drilling (i.e. 3-5 km) and further to ultra-deep drilling (i.e. 5-10 km).
  • EPB has a higher performance for drilling through hard rock formations when compared with rotary drilling and EPB drilling heads have a longer life span than a rotary drill-bit.
  • the principle of EPB is to apply electro-pulses in the range between 100 and 1000 kV between a high-voltage electrode and a grounded electrode. Each pulse represents an energy in the range between 1 to 10 kJ.
  • the electrodes are part of a drill bit arrangement which forms part of the drill head.
  • the electro pulses have a typical duration in the nanosecond range, for example a pulse duration of 200 ns, and are applied at intervals in the millisecond range, for example a pulse interval of 100 milliseconds.
  • An electrical discharge passing through for example a rock results in the rock mass to fracture into smaller pieces, i.e. rock cuttings.
  • the electrodes together with the rock portion to be excavated are immersed in a drilling liquid, also named discharge liquid.
  • the drilling liquid is a liquid that has a conductivity that is lower than the conductivity of the material in which the drilling is carried out, such that the generated electric fields are steered into the rock in the region of the electrodes.
  • An example of a typical fluid used as a drilling liquid for EPB is transformer oil.
  • a problem related to large diameter holes is the drill speed that can be obtained, i.e. the number of meters per hour that can be drilled.
  • the drill speed In order to limit the total drilling time for a 5 to 10 km hole, the drill speed should be of the order of several meters to tens of meters per hour and this high drill speed should be maintained during the entire drilling process. For a 50 cm diameter hole, this corresponds to excavating several m 3 of rock per hour, which is challenging with current technology. It is also important that the high drill speed is maintained when drilling to deeper regions where the environmental conditions become more severe. Examples of environmental conditions are pressure, temperature and the potential occurrence of harder rock formations at large depths.
  • a rock debris evacuation system should be able to evacuate at a high rate a large volume of rock cuttings mixed with drill liquid over a long distance from the bore hole up to the surface.
  • the primary rock cuttings should have a diameter in the range of 2 to 3 cm and the primary rock cuttings should be evacuated without delay after the formation of the cuttings such that no secondary smaller rock cuttings can be formed.
  • a further problem is related to the use of the drilling liquid, such as transformer oil. Filling up the borehole up to the surface requires large quantities of drill liquid and hence the drill liquid becomes a non-negligible cost of the EPB system.
  • the drill liquid can also be a potential risk of pollution.
  • an EPB apparatus comprising two concentric pipes separated by electric insulators is disclosed, and wherein an inner pipe corresponds to a high-voltage pipe coupled to a high-voltage electrode and an outer pipe is grounded and coupled to a ground electrode.
  • the high voltage pipe is coupled with a pulse generator that is located at the surface, i.e. outside the bore hole.
  • a debris collecting device is described wherein the debris is evacuated through a space between the wall of the drilled hole and part of an external wall of the drilling apparatus.
  • an EPB-based drilling apparatus is described using a down hole pulse generator and wherein electrodes are moveable relative to each other in order to secure bottom contact for each of the electrodes.
  • a number of hydraulic nozzles for nozzle jetting of the drill fluid and thereby directing and lifting the rock cuttings are described as well.
  • the rock cuttings are removed from the periphery of the bottom-hole up to the surface by pumping the drill fluid together with the cuttings through an annular spacing between the wall of the drilled borehole and an outer perimeter of the drilling apparatus.
  • a drill head is proposed for drilling bore holes of a diameter of 36 cm using EPB and wherein a high-voltage pulse generator is integrated in the drill head.
  • the drill fluid is supplied to the electrodes through a central pipe and the rock cuttings together with the drill liquid are evacuated through an annular spacing between the drill head and the wall of the drilled borehole.
  • the drilling apparatus of this invention is particularly suitable for the drilling of bore-holes with such large diameters, it is also suitable for drilling bore-holes with smaller diameters of for example 5, 10 or 20 cm or the like.
  • the present invention is based on insights of the inventors and based on experiments performed. These insights supported by the experiments resulted in the conclusion that by limiting the volume of the circulating drilling liquid, not only can be saved on the cost price of the drilling liquid, being for example a transformer oil or a bio-oil, but also that the excavated matter, e.g. rock cuttings, can be evacuated in a more efficient way by providing dedicated return pipes for evacuating the rock cuttings mixed with drill fluid from a bottom portion of the borehole.
  • the excavated matter e.g. rock cuttings
  • a drill head for electro-pulse- boring suitable for drilling a borehole having a diameter equal or larger than 50 cm is provided.
  • the drill head for electro-pulse-boring comprises a high-voltage pulse generator enclosed in a hermetically sealed container such that the container is tillable with an electrically insulating fluid.
  • the container comprises i) a circumferential wall extending along a central axis coaxial with a drilling axis of the drill head and ii) a first and a second axial cover for sealingly closing respectively a first and a second end of the circumferential wall.
  • a drill bit is mechanically coupled to the container and comprises an electrode assembly electrically coupled with the high-voltage pulse generator for receiving high-voltage pulses.
  • a supply pipe is configured for supplying drill liquid to the drill bit such that when in operation a borehole bottom portion is filled with drill liquid so as to immerse the drill bit with drill liquid.
  • the supply pipe is mechanically coupled to the container and traversing through the container from the first axial cover to the second axial cover.
  • the supply pipe is traversing the container along the central axis from a supply pipe entrance portion traversing through the first axial cover to a supply pipe exit portion traversing through the second axial cover.
  • the drill head according to the invention comprises a circumferential seal for separating drill liquid in the borehole bottom portion from a stabilisation liquid that is filing up the borehole up to a surface. At least a portion of the circumferential seal is surrounding a part of the circumferential wall of the container.
  • the circumferential seal extends in a direction parallel with the central axis.
  • the circumferential wall of the container has a height measured along the central axis between the first and the second end of the circumferential wall.
  • the circumferential seal can also be construed as extending in a height direction of the container, being parallel with the central axis, along part of the height of the container.
  • the drill head according to the invention further comprises one or more return pipes for evacuation excavated matter mixed with drill liquid from the borehole bottom portion. These one or more return pipes are mechanically coupled to the container.
  • the excavated matter comprises for example rock cuttings when a borehole is drilled through rock formations.
  • the skilled person will be capable of configuring a cross sectional area of the return pipes relative to the cross sectional area of the supply pipe such that supply of the drilling liquid is not hampered by evacuation of the excavated matter, or in other words wherein supply of the drilling liquid and evacuation of the excavated matter are equilibrated.
  • the return pipe or pipes can be coupled with a return channel of a drill string for transporting the excavated matter mixed with drill fluid from the drill head to the surface, thereby maintaining the increased flow speed to evacuate the excavated matter from the borehole up to the surface.
  • the one or more return pipes are either coupled or partly coupled to an inner side of the circumferential wall of the container, while in other embodiments the one or more return pipes are coupled to the outside of the circumferential wall of the container.
  • the one or more return pipes are traversing the container and each of the return pipes comprises i) a pipe entrance portion traversing through the second axial cover and ii) a pipe end portion, and wherein the pipe end portions of the return pipes are traversing through the first axial cover.
  • the pipe end portions can also be coupled to a common feedthrough for traversing through the first axial cover.
  • the entrance of the return pipes are located on top of the electrode region allowing to efficiently evacuate the rock cuttings.
  • the height of the bottom portion of the borehole to be filled with drill liquid can be limited to a strict minimal height which is the distance between the borehole bottom where the electrodes are resting and the bottom cover of the container.
  • an electro-pulse boring system comprises a drill head for electro-pulse-boring as discussed above, a lifting device located at the surface and configured for lifting the drill head from the borehole, a drill string assembly, a drill liquid circulation system.
  • the electro-pulse boring system will further comprise any additional parts known to the skilled person needed for the functioning of the boring system, for example without being limited thereto, a dedicated power supply, a mud supply system for stabilising the bore hole, a separator for separating the drilling liquid from the excavated matter etc.
  • the drill string assembly comprises at least i) a feed channel for supplying drill liquid from the surface to the drill head, ii) a power cable, running from the surface to the drill head for supplying power to the electro-pulse generator and iii) one or more return channels for transporting a mixture of excavated matter and drill liquid up to the surface.
  • the drill liquid circulation system comprising at least i) a drill liquid reservoir, ii) a pump for pumping drill liquid from the drill liquid reservoir to the drill head through the feed channel of the drill string assembly, and iii) a drill liquid recovery device configured for receiving the mixture of excavated matter and drill liquid from the one or more return channels of the drill string assembly and configured for separating the excavated matter from the drill liquid and transporting the recovered drill liquid to the reservoir.
  • Fig.1 shows a cross-sectional view of a first embodiment of a drill head
  • Fig.2 shows a cross-sectional view of part of a second embodiment of a drill head according to the present invention
  • Fig.3 shows an isometric view of a further example of a drill head according to the invention
  • Fig.4 shows an isometric view of an example of drill bit comprising an
  • FIG.5 shows a projection of a further example of a drill bit comprising an
  • Fig.6 schematically illustrates an example of a container of an electro-pulse generator.
  • Coupled When the wording “coupled”, “mechanically coupled” or “electrically coupled” is used, it is to be construed as either directly or indirectly coupled.
  • An indirectly coupling between a first and a second element can for example be made by placing a third element in between the first and second element.
  • the present invention is related to a drill head for electro-pulse-boring of a borehole having a diameter equal or larger than 40 cm, preferably equal or larger than 50 cm.
  • the drill head is a component that is part of an electro-pulse boring system. Some components of the system are located on the surface and some components are located inside the borehole.
  • the EPB boring system typically comprises at least a lifting device, a drill string assembly, a high voltage supply, a drill liquid circulation system and a drill head.
  • the drill head is the component that is lowered in the bore hole and comprises a drill bit with electrodes or drill tips.
  • a high-voltage generator is required and generally this generator can either be located on the surface or it can be part of the drill head and be lifted down the borehole together with the drill bit.
  • the drill head of the present invention is a drill head configuration that comprises the high-voltage pulse generator, which for these configurations is generally named down-hole generator.
  • Drill head general
  • FIG.1 Examples of a drill head 1 according to the present invention are schematically shown on Fig.1 to Fig.3. Not all components of the drill head are shown on these figures, only those components needed for understanding the invention are shown.
  • Reference number 100 on Fig.1 schematically illustrates, as an example, a rock formation through which a hole is to be drilled.
  • the drill head 1 comprises a high- voltage pulse generator enclosed in a hermetically sealed container 10 such that the container can be filled with an electrically insulating fluid 90.
  • An electrically insulating fluid 90 is for example nitrogen or an inert gas.
  • the container 10 of the high-voltage generator comprises a circumferential wall 1 1 extending along a central axis Z.
  • the central axis Z is coaxial with a drilling axis of the drill head 1 .
  • a first axial cover 12 and a second axial cover 13 are sealingly covering respectively a first and a second end of the circumferential wall 1 1 .
  • the first and second axial cover can respectively also be named top and bottom cover in the sense that the bottom cover is positioned deeper in the borehole than the top cover.
  • the high-voltage pulse generator enclosed inside the container 10 is not shown on Fig.1 .
  • the circumferential wall 1 1 is for example formed by a hollow pipe and hence has the shape of a cylinder.
  • the circumferential wall 1 1 defining the outer wall of the container 10 can have any other shape such as a prism or a square.
  • the circumferential wall of the container has a height measured along the central axis Z between the first and the second end of the circumferential wall.
  • the height of the container can be several meters, depending on the size of the high-voltage pulse generator.
  • the drill head 1 further comprises a drill bit that is mechanically coupled to the container 10, preferably coupled to the second end of the circumferential wall, for example by attachment to the axial cover 12.
  • the drill bit is mechanically supported through the container, preferably through the bottom side of the container 10.
  • the drill bit comprises an electrode assembly 40 that is electrically coupled with the high-voltage pulse generator for receiving high-voltage pulses.
  • the electrode assembly 40 includes a ground electrode 41 and a high-voltage electrode 42, as shown for example on Fig.2 and Fig.3.
  • the circumferential wall 1 1 and the first 12 and second 13 axial cover are typically made or partly made of a metal such as stainless steel and are electrically grounded.
  • the ground electrode of the electrode assembly 40 is then coupled with the second cover or with the circumferential wall in order to form a grounded connection.
  • the ground electrode is for example welded to the second cover plate or welded to a portion of the circumferential wall.
  • a high- voltage feed-through is passing through the second axial cover 13 and is configured for providing high-voltage to the high-voltage electrode 42.
  • a drill liquid also named discharge liquid
  • the drill head comprises a supply pipe 31 for supplying drill liquid to the drill bit such that when in operation a borehole bottom portion 70 is filled with drill liquid so as to immerse the drill bit with drill liquid.
  • the supply pipe is traversing through the container 10 of the high-voltage generator from the first axial cover 12 to the second axial cover 13.
  • the supply pipe 31 is mechanically coupled to the container.
  • the supply pipe 31 is traversing the container 10 along the central axis Z from a supply pipe entrance portion traversing through the first axial cover 12 to a supply pipe exit portion traversing through the second axial cover 13.
  • any other arrangement of the supply pipe with respect to the container considered suitable by the skilled person may be used as well.
  • the drill head 1 As further illustrated on Fig. 1 and Fig.3, the drill head 1 according to the present disclosure is characterized in that it comprises a circumferential seal 50 for separating drilling liquid in the borehole bottom portion 70 from a stabilisation liquid 80 that is filing up the borehole up to the surface. At least a portion of the circumferential seal 50 is surrounding part of the circumferential wall 1 1 .
  • the use of the word surrounding has to be construed as enclosing.
  • the circumferential seal 50 surrounding the cylindrically shaped circumferential wall corresponds to encircling the circumferential wall by 360°.
  • the circumferential seal 50 surrounding part of the circumferential wall 1 1 of the container is also extending in a height direction of the circumferential wall, i.e. in a direction parallel with the central axis Z.
  • the height direction of the container can also be construed as an axial direction of the container, which is a direction parallel with the central axis Z of the container.
  • the entire circumferential seal 50 is surrounding part of the circumferential wall 1 1 of the container.
  • a first portion of the circumferential seal 50 is surrounding part of the circumferential wall of the container and a second portion of the circumferential seal is surrounding the drill bit.
  • the second portion of the circumferential seal is located in the bottom portion of the borehole where the drill bit is located.
  • the stabilisation liquid 80 is for example water.
  • the stabilisation liquid stabilises the wall of the bore hole.
  • the drill head according to the present disclosure is therefore further characterized that it comprises one or more return pipes 32a, 32b for evacuation excavated matter, such as rock cuttings, mixed with drill liquid from the borehole bottom portion 70.
  • the drill head according to the present disclosure comprises two or more return pipes mechanically coupled to the container 10.
  • the container 10 together with the supply pipe 31 and the return pipes 32a, 32b is illustrated in more detail on Fig.6.
  • the electro-pulse generator enclosed inside the container is not shown on Fig.6.
  • the drill head according to the present invention is suitable to drill through rock, e.g. sandstone, granite and other hard rock materials, and evacuate the rock cuttings via the return pipes.
  • the drill head is of course also suitable to drill through any sediment underground layer and evacuate debris through the return pipes.
  • the circumferential seal is for example made or partly made out of an elastic material and/or a compressible material.
  • the seal is for example made out of rubber.
  • the circumferential seal 50 is inflatable in order to provide for a robust sealing.
  • the return pipes 32a, 32b are made of a metal such as stainless steel.
  • the supply pipe 31 is made of or partly made of an electrically insulating material such as fiberglass or another insulator.
  • each of the return pipes 32a, 32b comprises a pipe entrance portion traversing through the second axial cover 13 and a pipe end portion traversing through the first axial cover 12. Holes can for example be made through the first and second axial cover to receive the end portions of the return pipes and the end portions can be placed through the holes and welded such that the interior of the container remains hermetically sealed for receiving the electrically insulating fluid 90.
  • each of the one or more return pipes is coupled or partly coupled to an inner side of the circumferential wall 1 1.
  • the return pipes can be welded to the inner side of the circumferential wall 11.
  • an inner circumferential side of the circumferential seal 50 is attached to an outer side of the circumferential wall 1 1.
  • the inner side of the circumferential seal can be attached to the circumferential wall by using metallic ring connectors, not shown on Fig.1.
  • the pipe end portions of the return pipes are coupled to a common feedthrough for traversing through the first axial cover 12.
  • the feedthrough can then be further coupled to a single return channel to transport the rock cuttings mixed with drill liquid to the surface.
  • only one dedicated hole needs to be made in the first axial cover for receiving the common feedthrough.
  • FIG.2 A cross-sectional view of a second embodiment of a drill head according to the present invention is shown on Fig.2.
  • the return pipes 32a and 32b are mounted on the outside of the circumferential wall 1 1 of the container.
  • the circumferential seal is not shown on Fig.2.
  • FIG.3 an isometric view of a drill head is shown comprising return pipes 32a and 32b mounted on the outside of the circumferential wall of the container 10.
  • a circumferentially extending flange 15 is surrounding and attached to the circumferential wall 1 1 so as to form a collar around the circumferential wall 1 1 .
  • the circumferentially extending flange is for example welded to the circumferential wall.
  • the circumferentially extending flange 15 is for example a ring-shaped flange.
  • the circumferentially extending flange 15 is used for both coupling the circumferential seal 50 and for coupling the return pipes as discussed below.
  • the circumferential seal 50 has a first portion, being the portion that is attached to the extending flange 15, and a second portion surrounding the drill bit.
  • the one or more return pipes 32a, 32b are attached to the outer side of the circumferential wall 1 1 , for example by welding.
  • the circumferentially extending flange comprises for each of the return pipes a corresponding feedthrough opening and each feedthrough opening is receiving a corresponding return pipe entrance portion. After placing a return pipe entrance portion through a hole of the circumferentially extending flange it can be welded to the circumferentially extending flange 15.
  • the invention is not limited to the number of return pipes but there should be at least one return pipe, preferably at least two pipes. The reason being that due to the fact that there is not much space between the circumferential wall and the borehole, the diameter of the return pipes 32a, 32b is limited and more than one pipe is needed for obtaining a combined drill liquid evacuation capacity that is equal or larger than the drill liquid supply capacity through the supply pipe 31.
  • the one or more return pipes have a cross sectional area configured such that the sum of the cross sectional areas of each of the return pipes is equal to a cross sectional area of the supply pipe within an accuracy of 30%, preferably within an accuracy of 25%, more preferably within an accuracy of 20%.
  • the electro-pulse generator comprises a plurality of capacitors forming part of what is named a Marx generator, known in the art and disclosed in for example RU2477370.
  • the plurality of capacitors are repetitively charged and de- charged and the high-voltage that is outputted is the sum of the voltages on the capacitors.
  • Such a generator is optimized to generate high-voltage pulses with short pulse duration time, typically up to 300 ns, for example in the 100 to 200 ns range or lower, as required for EPB.
  • the electro-pulse generator of the drill head according to the invention is configured for generating high-voltage pulses having a voltage in a range between 100 kV and 1000 kV, preferably in a range between 300 kV and 600 kV, more preferably in a range between 400 and 600 kV.
  • each of the capacitors have a ring-shape and are circumscribing the supply pipe 31.
  • the drill bit 20 comprises an electrode assembly 40.
  • the present invention is however not limited to the specific type of electrode assembly 40 or the specific shape or geometry of the electrode assembly 40 , as illustrated on fig. 4 and 5.
  • the electrode assembly has for example a circular perimeter with an outer diameter DE measured in a plane perpendicular to the central axis Z, and wherein DE 3 40 cm, preferably DE 3 50 cm. This outer diameter of the electrode assembly defines the diameter of the borehole that can be drilled.
  • the circumferential wall 11 of the container has a cylindrical shape with an outer diameter DPG and wherein generally DPG ⁇ DE.
  • the outer diameter DPG has to be smaller than DE such that there is at least sufficient space for placing the circumferential seal 50.
  • the perimeter of the electrode assembly 40 is not limited to a circular shape but the perimeter can for example also be an oval, a square or any other shape depending on the required cross-sectional shape for the borehole.
  • a single-segment electrode assembly 40 is an electrode assembly comprising a single ground- electrode 41 and a single high-voltage electrode 42, as shown for example on fig-3.
  • FIG. 4 An example of a drill bit 2 comprising a single-segment electrode assembly is shown on Fig. 4.
  • the electrode assembly shown on Fig.4 comprises a single ground electrode and a single high-voltage electrode formed by respectively a plurality of ground electrode tips 41 a and a plurality of high- voltage electrode tips 42a. These ground and high-voltage electrode tips are radially positioned with respect to the central axis of the drill head.
  • the drill bit 20 comprise an electrode assembly wherein the ground and high-voltage electrodes have respectively a circumferential ground electrode component 41 b and a circumferential high-voltage electrode component 42b.
  • the circumferential ground electrode component 41 b and the circumferential high-voltage electrode component 42b are forming an outer perimeter of respectively the ground and high-voltage electrode.
  • These circumferential electrode components 42b, 42b have for example a circular shape as shown on Fig.5.
  • the electrode assembly 40 is not a single segment electrode assembly but a multi-segment electrode assembly comprising a plurality of electrode segments.
  • each of the electrode segments has a ground 41 and high-voltage 42 electrode.
  • the electrode assembly can comprise two, three, four or more electrode segments. The segments are preferably connected to each other so that they are capable of drilling as one entity.
  • the electrode assembly is circular and can comprise two, three, four or more electrode segments which are mechanically coupled to form a unity.
  • the electrode segments may be arranged to be individually steerable or controllable to permit directional boring, or they may be controllable as a whole.
  • the high-voltage pulse generator is configured for individually powering each of the electrode segments.
  • a first advantage of using a multi-segment electrode is that the power pulses generated by the high-voltage pulse generator can sequentially be applied to each of the plurality of segments and hence the delivered power can be used more efficiently and be better distributed over the entire cross-sectional area of the borehole to be drilled. Remark that if the diameter of the bore hole is increasing, for a given operational frequency of the high-voltage pulse generator, the total power needed to excavate the borehole is in a first approximation quadratically increasing with the diameter of the borehole.
  • the use of a segmented electrode allows to divide the total power to be delivered among the various segments.
  • a drill speed is envisaged which approaches or is the same as a conventional drill speed used for the boring of bore holes with a smaller diameter.
  • the use of a segmented drill head permits limiting the electric power that is supplied to each segment as well as the pulse frequencies to conventionally used values. Drilling of bore holes with increasing diameters would otherwise involve an almost exponential increase of the electric power to be delivered by the high-voltage pulse generator with increasing bore hole diameter.
  • a second advantage of using multi-segment electrode assemblies is that the drill direction can be changed or corrected by a proper control of the individual electrode segments. For example, the drill head direction could be changed by delivering more pulses to one of the segments compared to the other segments.
  • the electrode assembly is segmented and one of the electrode segments is configured for drilling a locally enlarged bore hole resulting in the formation of a borehole having a longitudinal groove or channel in the wall of the borehole.
  • the local enlargement may serve as a channel for evacuating the excavated matter mixed with drill liquid.
  • the electrode assembly 40 comprises a ground-electrode 41 and a high-voltage electrode 42 configured for resting on a surface of the borehole bottom portion.
  • the electrodes form a supporting structure for supporting the drill head when boring the bore hole.
  • the ground and/or high-voltage electrode comprise electrode tips configured for resting on the surface of the borehole bottom portion.
  • the inventors have performed a series of tests with a drill head according to the present invention to investigate the evacuation efficiency of rock cuttings.
  • a prototype drill head as shown on Fig.3 was used for testing purposes.
  • the supply pipe 31 used has a diameter of 10,16 cm, i.e. 4 inches, and the two return pipes have a diameter of 6,35 cm, i.e. 2.5 inches.
  • the drill head was dimensioned to drill bore holes of 50 cm which results in a bore bottom portion having a volume of 54977 cm 3 and which was filled with 54 liter of drill liquid.
  • the drill liquid supply rate was optimized in order to suck a maximum rate of rock cutting through the two return pipes.
  • An optimum rock cutting recovery was obtained with a drill liquid supply rate of 1000 liter/minute which resulted in a recuperation of 2,35 m 3 of rock cuttings per hour.
  • the drill head used for the testing uses a Marx-type high-voltage generator providing pulses of 500kV at a rate between 1 up to 25 Hz. Further experiments have demonstrated that with the drill bit having a 50 cm diameter electrode configuration used in combination with the high-voltage generator, the drill head is capable of crushing 2,35 m 3 / hour of rock.
  • the evacuation system according to the invention using return pipes combined with a seal to reduce the total drill liquid volume is capable of efficiently evacuating the rock cuttings at a rate that is equal to the rate the rock cuttings are produced. With such a system a drill speed of 12 m/hour or more can be reached.
  • the drill head is a component of an EPB system.
  • An EPB system comprises besides the drill head also a lifting device located at the surface and configured for lifting the drill head from the borehole.
  • the EPB system also comprises a drill string assembly comprising i) a feed channel for supplying drill liquid from the surface to the drill head, ii) a power cable which may for example run from the surface to the drill head for supplying power to the electro-pulse generator, and iii) one or more return channels for transporting a mixture of excavated matter and drill liquid up to the surface.
  • the EPB system also comprises a drill liquid circulation system comprising at least i) a drill liquid reservoir, ii) a pump for pumping drill liquid from said drill liquid reservoir to the drill head through said feed channel of the drill string assembly, and iii) a drill liquid recovery device configured for receiving said mixture of excavated matter and drill liquid from said one or more return channels of the drill string assembly and configured for separating the excavated matter from the drill liquid and transporting the recovered drill liquid to the reservoir.
  • a drill liquid circulation system comprising at least i) a drill liquid reservoir, ii) a pump for pumping drill liquid from said drill liquid reservoir to the drill head through said feed channel of the drill string assembly, and iii) a drill liquid recovery device configured for receiving said mixture of excavated matter and drill liquid from said one or more return channels of the drill string assembly and configured for separating the excavated matter from the drill liquid and transporting the recovered drill liquid to the reservoir.
  • the supply pipe entrance portion of the supply pipe comprises a first coupling means configured for coupling with the feed channel of the drill string transporting the drill fluid from the surface to the drill head.
  • the coupling means can for example be a coupling flange.
  • each of the pipe end portions of the return pipes traversing the first axial cover comprises a second coupling means and wherein the second coupling means is configured for coupling with the return channel of the drill string transporting the excavated matter mixed with drill fluid from the drill head to the surface.
  • the common feedthrough comprises a second coupling means configured for coupling with the return channel of the drill string.

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  • Geochemistry & Mineralogy (AREA)
  • Mechanical Engineering (AREA)
  • Earth Drilling (AREA)

Abstract

L'invention concerne une tête de forage (1) pour le forage électro-pulsé. La tête de forage (1) comprend un générateur d'impulsions haute tension enfermé dans un récipient hermétiquement fermé (10) et un trépan accouplé mécaniquement au récipient (10). Le trépan comprend un ensemble électrode (42) couplé électriquement au générateur d'impulsions haute tension. La tête de forage (1) comprend un tuyau d'alimentation (31) pour fournir du liquide de forage au trépan de telle sorte que, lors du fonctionnement, une partie inférieure de trou de forage est remplie de liquide de forage de façon à immerger le trépan avec le liquide de forage. La tête de forage comprend un joint circonférentiel (50) pour séparer le liquide de forage dans la partie inférieure de trou de forage d'un liquide de stabilisation qui remplit le trou de forage (100) jusqu'à une surface. Au moins une partie du joint circonférentiel entoure une paroi circonférentielle (11) du récipient. La tête de forage comprend en outre un ou plusieurs tuyaux de retour (32a, 32b) pour l'évacuation de matière excavée mélangée au liquide de forage à partir de la partie inférieure de trou de forage, et le ou les tuyaux de retour étant accouplés mécaniquement au récipient (10).
PCT/EP2020/063742 2019-05-17 2020-05-16 Tête de forage pour forage électro-pulsé WO2020234202A1 (fr)

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CN202080036556.XA CN114174630A (zh) 2019-05-17 2020-05-16 用于电脉冲镗孔的钻头

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EP19175222.9 2019-05-17
EP19175222.9A EP3739163B1 (fr) 2019-05-17 2019-05-17 Tête de forage pour perçage par électro-impulsion

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CN114174630A (zh) 2022-03-11
EP3739163B1 (fr) 2021-06-30

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