阅读说明：本技术 借助放电进行旋转钻孔的系统 (System for rotary drilling by means of electrical discharges ) 是由 F·巴约尔 B·德拉马内 J-L·高森 C·格普菲特 于 2015-02-20 设计创作，主要内容包括：本发明涉及用于旋转钻探的向下钻进装置,其包括安装在一系列杆(4)端部处的发电机(5)；机械地和电气地连接到所述发电机的脉冲发生器(6)；电动钻探工具(7)；以及电滑动开关系统(9)。本发明用于通过放电进行的进行钻探的领域。(the invention relates to a downhole device for rotary drilling, comprising a generator (5) mounted at the end of a series of rods (4); a pulse generator (6) mechanically and electrically connected to the generator; an electric drilling tool (7); and an electrical sliding switch system (9). The invention is used in the field of drilling by electric discharge.)

1. Downhole device for rotary drilling, comprising:

-an electric generator (5), which generator (5) is mounted at the end of a drill string consisting of drill pipe and/or drill collar and converts the hydraulic energy of the drilling fluid into electric energy;

-a pulse generator (6), said pulse generator (6) being mechanically and electrically connected to said generator and supplying power to an electrode system carried by said drilling tool;

-an electric drilling tool (7), said electric drilling tool (7) being mechanically and electrically connected to said pulser, a drill string consisting of drill pipes and/or drill collars driving said electric drilling tool in rotation and comprising a system consisting of active electrodes (12, 12a) and passive electrodes (11); and

-an electrical sliding switch system (9).

2. The device according to claim 1, characterized in that the sliding switch system (9) incorporates: (i) the electric drilling tool (7), or (ii) an interface between the electric drilling tool (7) and the pulse generator (6), or (iii) the pulse generator (6), or (iv) between the pulse generator (6) and the generator (5), or (v) the generator (5), or (vi) above the generator (5).

3. the device of claim 1 or 2, comprising two slide switches:

-a first electric sliding switch (9s), said first electric sliding switch (9s) being interposed between the portion of the generator that converts hydraulic energy into mechanical energy and the portion of the generator that converts mechanical energy into electric energy, such that, when in the "on" position, it prevents the generation of electricity even if drilling fluid circulates inside the hydraulic compartment; and

-a second electric sliding switch (9i), said second electric sliding switch (9i) being located at the electric drilling tool, such that when in the "open" position, it forces the discharge of the capacitance (16) of the pulser and prevents the charging thereof, even when the electric compartment is generating electric current.

4. A device according to any one of claims 1-3, characterized in that the rotation of the electric drilling tool (7) combines the mechanical effect of the passive electrode (11) with the electrical discharge effect.

5. A device according to any of claims 1-4, characterized in that the rotation of the electric drilling tool (7) sweeps the entire surface of the borehole with a radial arc occurring between the passive (11) and active (12, 12a) electrodes.

6. a device according to any one of claims 1 to 5, characterised in that the sliding switch, which acts as an electric switch, is normally opened by means of a mechanical spring (14) which keeps the sliding switch open, the power circuit of the pulse generator being kept open by a circuit connecting the two terminals of the capacitor (16) to a discharge resistor, keeping the capacitor in a "short-circuited" state.

7. The apparatus of claim 6 wherein the "normally open" position of the slide switch is enhanced by injecting drilling fluid into the housing to trigger a positive action from the surface.

8. The apparatus of any one of claims 1 to 7, wherein triggering a positive direction from the surface comprises applying a weight on the electric drilling tool, thereby enabling the switch to switch from an open position to a closed position.

9. The apparatus of any one of claims 1 to 8,

-the generator (5) comprises a turbine or a positive displacement motor, the flow of drilling fluid driving the rotation of the rotor of the motor, which in turn drives the rotor of the alternator,

-the interface between the rotor of the turbine or the motor and the rotor of the alternator comprises an electrical slide switch allowing a mechanical clutch.

10. the device according to any one of claims 1 to 9,

-said system of active and passive electrodes comprises two groups of electrodes electrically insulated from each other but mechanically connected to each other from an axial point of view and an angular point of view, said groups of electrodes comprising:

(i) a set of passive electrodes, ground electrodes, and (ii) a set of active electrodes, high voltage electrodes; or

-said system of active and passive electrodes comprises two groups of electrodes electrically insulated from each other, but mechanically decoupled from each other from an angular point of view, but not decoupled from an axial point of view, said groups of electrodes comprising: (i) a set of passive electrodes, ground electrodes, located at the periphery of the electric boring tool, and (ii) a set of active electrodes, high voltage electrodes, centrally located in the electric boring tool and not mechanically connected to the set of passive electrodes so as not to be driven in rotation by the passive electrodes; or

-said system of active and passive electrodes comprises two groups of electrodes electrically insulated from each other, but mechanically decoupled from each other from an angular point of view and from an axial point of view, said groups of electrodes comprising:

(i) A set of passive electrodes, ground electrodes, located within the periphery, and (ii) a set of active electrodes, high voltage electrodes, located centrally within said electric drilling tool, equipped with axial tracks, preferably several centimeters long, and subjected to the force of a corrugated spring that enables continuous contact of the electrodes with the rock; or

-the system of active and passive electrodes comprises two sets of electrodes electrically insulated from each other, but mechanically attached to each other from an angular point of view, but not from an axial point of view, the set of electrodes comprising: (i) a set of passive electrodes, ground electrodes, and (ii) a set of active electrodes, high voltage electrodes, positioned eccentrically with respect to the axis of the electric drilling tool, equipped with an axial trajectory, preferably several centimeters long, and subjected to the force of a corrugated spring that enables the electrodes to be in continuous contact with the rock.

11. The device according to any one of claims 1 to 10, characterized in that the terminal portion of the electric drilling tool (7) comprises an internal chamber (36) devoid of any solid material other than the electrodes.

12. The apparatus according to any of the claims 1 to 11, characterized in that the axis of the pulse generator (6) intersects an axial hollow tube of insulating material, which is mechanically connected to the lower part of the pulse generator with a metal tube, so that the continuity of the tube ensures the transmission of the drilling fluid and the reception of the electrical discharge from the pulse generator by the lower metal tube (preferably only this tube).

13. An arrangement as claimed in any one of claims 1 to 12, characterized in that the pulse generator (6) is a generator of the LTD linear converter driver type, or a Marx generator or TESLA converter.

14. An arrangement according to claim 12 or 13, characterized in that several modules consisting of energy storage means (preferably capacitors) and power switches (preferably gas discharge tubes) are stacked on top of each other in the annular space between the hollow tube and the outer metal envelope.

15. The apparatus of claim 14, wherein the power switch is comprised of a ring electrode having the form of a ring.

16. The device according to any one of claims 1 to 15, wherein the device further comprises an insulating connector consisting of two metal parts, an upper part and a lower part, the two metal parts being separated by an insulating material and nested between the two parts to transfer axial stresses and torsional stresses between the upper part and the lower part.

17. A device according to any one of claims 1 to 16, characterised in that the electrode comprises an insert (61) of hard and wear-resistant material, preferably of Polycrystalline Diamond Compound (PDC) type, or tungsten carbide type, and/or a metal matrix (62) comprising hard material (preferably diamond) powder or microparticles.

18. Apparatus for rotary drilling comprising an apparatus according to any of claims 1 to 17 incorporated at the end of a drill string comprising an assembly of drill pipe and possible drill collars for transmitting electrical energy; drilling equipment including a system for rotationally driving a drill string comprised of drill pipe and/or drill collars; and a drilling pump for injecting drilling fluid into a drill string of drill pipe and/or drill collar.

19. A drilling process carried out by turning the rotary drilling apparatus according to claim 18.

Technical Field

the present invention relates to a device and a process for rotary drilling by means of electric discharge and to certain elements of such a device.

Background

The traditional drilling technique employed in the fields of oil and gas exploration, mining, geothermal energy, civil engineering and other operations is a downhole rotary drilling tool, while exerting a thrust of several to tens of tons. Rotation of the boring tool is provided by rotating the entire drill string from the surface (a system known in the industry as "rotary drilling"), or using a bottom hydraulic motor (turbo drilling). The drilling tool used is a tricone type, PDC (polycrystalline diamond compact), or impregnated substrate. In all cases, the fragmentation of the rock is caused by mechanical effects. The rock cuttings produced by the tool rise to the surface in the space between the bore wall and the drill string (the annulus) by the upward flow of drilling fluid.

However, these techniques suffer from slow progression in certain very hard or very abrasive geological formations. To solve this problem, various alternatives have been devised for the conventional art. In these various designs, a technique has been proposed which is based on repeatedly injecting very high power electrical pulses directly into the ground through an electrode placed below the drilling tool. An arc is generated between the electrodes, which penetrates the ground and forms a plasma tunnel. The gas expansion created by the plasma causes the rock to break and form cuttings, which are then removed by fluid flow in a conventional manner. This technique has been known for a long time and has been given different names in the literature, such as "discharge pulse drilling", "plasma channel drilling process" or "electric pulse rock drilling apparatus".

Document US005845854A is a previous publication showing how the distance between the electrodes is optimized in terms of the voltage rise time. The document US6164388 gives equations for optimized operation and proposes an optimized power circuit design using semiconductor rectifiers. The document WO-A-03/069110 provides A sequence of magnitudes with respect to the electrical parameters (voltage, power, pulse period) of the process. However, these three patents suffer from a major weakness, namely the electrical power provided to the electrodes. Indeed, the pulse generators of these systems are located on the ground. It is therefore necessary for the transmission means (by means of cables or other systems) to connect the ground to the bottom borehole, which leads to problems of complexity and safety.

Some documents focus on the combination of this technology with other processes. Document US7416032 thus relates to a drilling system that performs drilling with electric discharges having a combination of electrical and mechanical effects. Document US7527108 relates to a portable system for drilling with electric discharges in the context of linear-metric borehole extraction. Document US7784563 relates to a system for drilling with electric discharges comprising a mechanism for maintaining continuous contact between the rock and the electrodes. Document EP2554780 proposes a combination of a system for drilling with electric discharges and a process for cooling and pulsing the drilling fluid. Document EP2554778 proposes a combination of a system for drilling with electric discharges, a sensor system for directional drilling and a LWD (drilling while recording) system.

All these documents present the same weaknesses: despite the presence of the pulse generator at the bottom of the borehole, the power required to power it is still provided from the surface by the cable. However, the presence of cables is a major obstacle that conflicts with operational use of these systems. Indeed, in the case of conventional drill strings, the presence of the cable impedes the rotation of the drill string. Such obstacles contradict the basic rules of expertise: the housing of the lever must be able to be turned at any time.

However, some documents suggest the possibility of employing a downhole power generator to power a system that drills by means of electrical discharge, such as for example documents US2009/00500371, US8109345 and US 7784563. However, these documents do not provide details on the operation of the system in such a configuration, the first document being only concerned with non-rotating systems. However, one of the main advantages of downhole generators is the ability to turn the drill string from the surface. Furthermore, these documents do not address the following three key issues in order to use downhole generators: control of system operation from the surface; when the drill string is lifted out, the safety of personnel is ensured against the risk of high voltage; and compatibility with the use of MWD (measurement while drilling) systems, which operate almost on these days, especially for oil well drilling.

Disclosure of Invention

Roughly described, the downhole apparatus is incorporated at the end of a drill string (an assembly of drill pipe and drill collar) and consists of four main components:

-a generator of electric energy,

-a pulse generator for generating a pulse of the electrical energy,

-an electrical slide switch for switching the electrical slide switch,

-an electric drilling tool.

The generator converts the hydraulic energy of the drilling fluid into electrical energy and delivers an electrical current that powers the pulser.

The pulse generator is generally composed of a capacitor and a power switch. The capacitor is fed by the generator. The power switch delivers repeated high voltage pulses to an electrode of the electric drilling tool.

Electric drilling tools are equipped with an electrode system. The electrode system consists of a high voltage electrode (electrically connected to the pulse generator capacitor) and a ground electrode.

the electrical slide switch enables to control the electrical operation of the system from the ground in a simple and reliable manner without transmission cables.

In parallel with electrical process implementations, the drill string is conventionally rotated from the surface, as no cables or other systems for transmitting electrical energy interfere with the movement. Thus, the drilling rig has a system that is fully compatible with the drilling equipment and standard procedures, while providing control over the electrical operation of the downhole system through the electrical slide switch.

The electrical slide switch allows remote control and enables the system to function and maintain safety.

The present invention therefore overcomes these drawbacks by providing a drilling system by means of electric discharges which does not require any electrical connection to the surface, allowing the operation of the downhole system to be controlled from the surface in a simple and safe manner. The present invention is also fully compatible with standard drilling equipment and conventional drilling procedures. Thus, the present invention provides safety, reliability and performance.

Accordingly, the present invention provides a downhole assembly for rotary drilling comprising:

-a generator mounted at the end of the drill string consisting of drill pipe and/or drill collar, which converts the hydraulic energy of the drilling fluid into electrical energy;

-a pulse generator mechanically and electrically connected to the generator, which supplies power to an electrode system carried by a drilling tool;

-an electric drilling tool, mechanically and electrically connected to the pulse generator, being drill pipe and ≤ being present

Or a drill string consisting of drill collars, which rotates the electric drilling tool and consists of an active and a passive electrode system; and

-an electrical sliding switch system.

According to one embodiment, the sliding switch system (9) incorporates: (i) the electric drilling tool (7), or (ii) an interface between the electric drilling tool (7) and the pulse generator (6), or (iii) the pulse generator (6), or (iv) between the pulse generator (6) and the generator (5), or (v) the generator (5), or (vi) above the generator (5).

According to one embodiment, the device comprises two slide switches:

-a first electrical sliding switch interposed between the part of the generator that converts hydraulic energy into mechanical energy and the part of the generator that converts mechanical energy into electrical energy, such that, when in the "on" position, the switch prevents the generation of electricity even if drilling fluid circulates inside said hydraulic compartment; and

-a second electric slide switch located at the electric drilling tool, such that when in the "open" position, the switch forces the capacitor (16) of the pulse generator to discharge and prevents the capacitor from charging, even when the electric compartment is generating electric current.

According to one embodiment, rotation of the electric drilling tool combines the mechanical effect of the passive electrode with the electrical discharge effect.

according to one embodiment, the rotation of the electric drilling tool sweeps the entire surface of the hole with a radial arc occurring between the passive and active electrodes.

According to one embodiment, the sliding switch, which acts as an electric switch, is normally open by means of a mechanical spring which keeps the sliding switch open, the power circuit of the pulse generator being kept open by a circuit connecting the two terminals of the capacitor to a discharge resistor, the capacitor being kept in a "short-circuited" state.

according to one variant, the "normally open" position of the slide switch is enhanced by injecting drilling fluid into the housing, triggering a positive action from the surface.

According to one embodiment, triggering a positive direction from the surface includes exerting a weight on the electric drilling tool, thereby enabling the switch to switch from an open position to a closed position.

According to one embodiment, in the device according to the invention:

The generator comprises a turbine or a positive displacement motor, the flow of drilling fluid driving the rotor of the motor in rotation, which in turn drives the rotor of the alternator,

-the interface between the rotor of the turbine or the motor and the rotor of the alternator comprises an electrical slide switch allowing a mechanical clutch.

according to one embodiment, in the device according to the invention:

-said system of active and passive electrodes comprises two groups of electrodes electrically insulated from each other but mechanically connected to each other from an axial point of view and an angular point of view, said groups of electrodes comprising: (i) a set of passive electrodes, ground electrodes, and (ii) a set of active electrodes, high voltage electrodes; or

-said system of active and passive electrodes comprises two groups of electrodes electrically insulated from each other, but mechanically decoupled from each other from an angular point of view, but not decoupled from an axial point of view, said groups of electrodes comprising: (i) a set of passive electrodes, ground electrodes, located at the periphery of the electric boring tool, and (ii) a set of active electrodes, high voltage electrodes, centrally located in the electric boring tool and not mechanically connected to the set of passive electrodes so as not to be driven in rotation by the passive electrodes; or

-said system of active and passive electrodes comprises two groups of electrodes electrically insulated from each other, but mechanically decoupled from each other from an angular point of view and an axial point of view, said groups of electrodes comprising: (i) a set of passive electrodes, ground electrodes, located within the periphery, and (ii) a set of active electrodes, high voltage electrodes, located centrally within said electric drilling tool, equipped with axial tracks, preferably several centimeters long, and subjected to the force of a corrugated spring that enables continuous contact of the electrodes with the rock; or

-the system of active and passive electrodes comprises two sets of electrodes electrically insulated from each other, but mechanically attached to each other from an angular point of view, but not from an axial point of view, the set of electrodes comprising: (i) a set of passive electrodes, ground electrodes, and (ii) a set of active electrodes, high voltage electrodes, positioned eccentrically with respect to the axis of the electric drilling tool, equipped with an axial trajectory, preferably several centimeters long, and subjected to the force of a corrugated spring that enables the electrodes to be in continuous contact with the rock.

According to one embodiment, the terminal portion of the electric drilling tool includes an internal chamber that is free of any solid material other than the electrodes.

According to one embodiment the axis of said pulse generator intersects an axial hollow tube of insulating material, which is mechanically connected to the lower part of said pulse generator by a metal tube, so that the continuity of said tube ensures the transport of drilling fluid and that said lower metal tube (preferably only this tube) receives the electrical discharge from said pulse generator.

According to one embodiment, the pulse generator is a generator of the LTD linear converter driver type, or a Marx generator or TESLA converter.

According to one embodiment, several modules consisting of an energy storage device (preferably a capacitor) and a power switch (preferably a gas discharge tube) are stacked on top of each other in an annular space between the hollow tube and an outer metallic envelope.

According to one variant, the power switch consists of a ring electrode, which has the form of a ring.

According to one embodiment, the device further comprises an insulating connector consisting of two metal parts, i.e. an upper part and a lower part, separated by an insulating material and nested between the two parts to transfer axial stresses and torsional stresses between said upper and said lower part.

According to one embodiment, the electrode comprises an insert of hard and wear-resistant material, preferably of the Polycrystalline Diamond Compound (PDC) type, or tungsten carbide type, and/or a metal matrix comprising hard material (preferably diamond) powder or microparticles.

The invention also relates to a rotary drilling rig comprising a downhole device according to the invention incorporated at the end of a drill string comprising an assembly of a drill pipe and possible drill collars for transmitting electrical energy; drilling equipment including a system for rotationally driving a drill string comprised of drill pipe and/or drill collars; and a drilling pump for injecting drilling fluid into a drill string of drill pipe and/or drill collar.

The invention further relates to a drilling process by turning the rotary drilling device according to the invention.

drawings

FIG. 1 depicts the overall system in a "slider positioned at the height of the power drill tool" configuration.

In this figure:

-1: drilling rigs equipped with a derrick, mast or other handling system,

-2: a system for rotating a drill string, the system comprising a drill string,

-3: pumps for injecting drilling fluid at high flow rates and pressures,

-4: a drill string consisting of a drill pipe and/or a drill collar,

-5: the power generator is provided with a power generator,

-6: a pulse generator for generating a pulse of a pulse signal,

-7: an electric drilling tool is provided with a drill bit,

-8: a stabilizer which is used for stabilizing the flow of the gas,

-9: an electrical slide switch positioned at the electric drilling tool,

-10: an electrode system.

Fig. 2 depicts the overall system in a "slider positioned between the generator and the pulse generator" configuration. The illustration of fig. 1 applies mutatis mutandis.

Fig. 3 depicts the overall system in a "two electrical slide switch" configuration. In this figure:

-9 s: upper electric slide switch

-9 i: lower electric slide switch

-5 a: hydraulic compartment

-5 b: electric compartment

-5: generator

Fig. 4 depicts a pulser and electric drilling tool in an "open-slider" configuration — a slider positioned at the height of the electric boring tool. In this figure:

-6: pulse generator

-8: stabilizer

-9: slide switch in "normally on" position

-11: grounding electrode

-12: central or compensated high voltage electrode

-13: insulator

-14: spring in uncompressed position

-15: corrugated spring in extended position

-16: capacitor with a capacitor element

-17: system for opening/closing a capacitor charging circuit and discharging a capacitor over a resistor in a "normally-closed" configuration

-18: hole for drilling fluid circulation

-19: system for mechanical transmission

fig. 5 depicts a pulser and electric drilling tool in a "closed slider" configuration — a "slider positioned at the height of the electric boring tool. In this figure:

-6: pulse generator

-8: stabilizer

-9 a: sliding switch in the "closed" position

-11: grounding electrode

-12: central or offset high voltage electrode

-13: insulator

-14 a: spring in compressed position

-15 a: bellows spring in compressed position

-16: capacitor with a capacitor element

-17 a: system for opening/closing a capacitor charging circuit and discharging a capacitor over a resistor in a "start-up" configuration

-18: hole for drilling fluid circulation

-19: system for mechanical transmission

-36: high pressure chamber

Fig. 6 depicts a power drill tool equipped with an electrical slide switch, located in a "high voltage electrode including a center or compensation electrode and several peripheral electrodes" configuration. In this figure:

-11: grounding electrode

-12: central or compensated high voltage electrode

-12 a: high voltage peripheral electrode

-13: insulator

-36: high pressure chamber

Fig. 7 depicts a detailed view of the mechanical and hydraulic part operation of the electrical slide switch when it is positioned at the power drill tool height. In this figure, in addition to the reference numerals already given in fig. 4 and 5:

-20: drilling fluid circulation channel

-21: force F1 exerted by spring 14 to open the slider

-22: force F2 generated by pressure [ P2(24) -P1(25) ] resulting from loss of fluid load within the insulator channel (20) and the portion S (23) exerting this pressure

-23: a surface on which a pressure is exerted, said pressure being generated by a fluid load loss [ P2(24) -P1(25) ] in the insulator channel (20)

-24: pressure P1 of drilling fluid upstream of insulator channel (20)

-25: pressure P2 of drilling fluid downstream of insulator channel (20)

Fig. 8 depicts an electrical slide switch positioned between the hydraulic compartment and the electrical compartment of the generator (disengaged position). In this figure:

-36: upper hollow driven shaft connected to hydraulic compartment rotor (turbine or downhole motor)

-37: upper bearing

-38: rotary motion of a hollow shaft driven by a rotor of a hydraulic compartment of a generator (turbine or downhole motor)

-39: sealing element

-40: mechanism for mechanically connecting between an upper and a lower part of a hollow shaft in a disengaged position

-41: lower bearing

-42: lower hollow shaft connected to the rotor of the generator electrical compartment (alternator)

-43: spring in uncompressed position

-47: drilling fluid circulation

Fig. 9 depicts an electrical slide switch positioned between (engaged position) the hydraulic compartment and the electrical compartment of the generator. In this figure:

-36: upper hollow driven shaft connected to hydraulic compartment rotor (turbine or downhole motor)

-37: upper bearing

-38: rotary motion of a hollow shaft driven by a rotor of a hydraulic compartment of a generator (turbine or downhole motor)

-39: sealing element

-41: lower bearing

-42: lower hollow shaft connected to the rotor of the generator electrical compartment (alternator)

-44: mechanism for mechanically connecting between upper and lower portions of a hollow shaft in an engaged position

-45: rotary motion of lower hollow shaft driven by upper hollow shaft

-46: spring in compressed position

-47: drilling fluid circulation

Fig. 10 depicts operational details of a portion of the circuit that discharges across the capacitor resistor away from the electrical slide switch. In this figure:

-26: generator

-27: circuit for discharging capacitance on resistor

-28: pulse generator

-29: electric drilling tool

-30: decoupling capacitor

-31: actuation of contactors by mechanical transmission systems

fig. 11 depicts one example of an electrode system configuration having a high voltage device including a single central compensation electrode. In this figure:

-32: grounding electrode

-33: high voltage electrode with central compensation

-34: distance D between the earth electrode point and the center electrode

Figure 12 depicts one example of an electrode system configuration having a high voltage device including a central compensation electrode and peripheral electrodes. In this figure:

-32: grounding electrode

-33: high voltage electrode with central compensation

-34: distance D between the earth electrode point and the center electrode

-35: peripheral high voltage electrode

fig. 13 depicts a cross-section of a pulse generator that is a Marx configuration generator with an annular gas discharge tube. In this figure:

-48: electrical interface between a pulse generator and a hollow axial high-pressure pipe

-49: ring electrode gas discharge tube

-50: insulator

-51: ring electrode of gas discharge tube

-52: drilling fluid circulation

-53: hollow axial tube in insulating material

-54: hollow axial high-pressure pipe

-55: outer metal shell

-56: comprising an energy storage device (capacitor) and a power switch (gas discharge tube)

fig. 14 depicts an insulating connector. In this figure:

-57: lower metal part

-58: upper metal part

-59: flow of drilling fluid

-60: insulator

Fig. 15 depicts a view of a portion of an electrode. In this figure:

-61：PDC

-62: impregnated substrate

Fig. 16 depicts a three-dimensional view of a tool according to the present invention.

Detailed Description

The invention will now be described in more detail, in the following description, without being limited thereto.

The present invention can be used in the following fields:

The oil sector (exploration and development of oil and/or gas fields),

the mining sector (exploration drilling),

geothermal sector (drilling of wells with low or high enthalpy),

Urban engineering departments (geological evaluation drilling, frozen earth hole drilling, etc.).

No special structural arrangement is required to incorporate the provided downhole apparatus at the end of a standard drill string (assembly of drill pipe and/or drill collars). It consists of the following elements:

-a generator (5),

-a pulse generator (6),

-an electric slide switch (9),

-an electric drilling tool (7).

A drilling rig (1) equipped with a derrick, mast or other handling system, a system (2) for rotating the drill string and a pump (3) for injecting drilling fluid at high flow and high pressure, and a drill string (4) of drill pipe and/or drill collar, which are connected to the downhole rig. A stabilizer (8) of standard design may be provided.

In parallel with the implementation of electrical processes, the drill string may be conventionally rotated from the surface (with a rotary table and kelly device or "power swivel") because no cables or other systems for transferring electrical energy interfere with this rotational motion. Thus, the drilling rig has a system that is fully compatible with the drilling equipment and standard procedures, while providing control over the electrical operation of the downhole system through the sliding of the tool.

in fig. 1, the electrical slide switch is positioned at the electric drilling tool, while in fig. 2, the electrical slide switch is positioned between the generator and the pulse generator.

Thus, the electrical slide switch may be positioned at the electric drilling tool or at an interface between different components of the system.

Fig. 3 also shows a configuration in which two electric slide switches are employed: one switch is located at the generator and the other switch is located at the electric drilling tool.

The use of downhole equipment is compliant with standard drilling procedures and the drilling equipment does not require any special structural arrangements.

Various components and procedures of the apparatus according to the invention will be described below.

The function of the generator (5) is to convert the hydraulic energy of the drilling fluid into electrical energy. In one of the different configurations considered (see, for example, fig. 3), the generator is constituted by:

-a hydraulic compartment (5a) of a downhole turbine or hydraulic motor type comprising a stator part and a rotor part,

-a mechanical interface for transmitting the rotary motion of the rotor from the hydraulic compartment to the rotor of the electrical compartment

-an electrical compartment (5b) which is itself subdivided in one possible configuration into two parts:

An alternator compartment comprising a stator part and a rotor part, the stator part carrying the windings of the alternator and the rotor part carrying the magnetic components,

A charger supplying a high voltage current, for example between 1kV and 50kV (preferably between 20kV and 40 kV), to the capacitance of the pulse generator.

In this configuration, the drilling fluid circulates between the stator and rotor portions of the hydraulic compartment and rotates the rotor. This in turn drives the rotor of the alternator. At the interface between the hydraulic and electrical compartments, the drilling fluid passes inside the alternator rotor, which is constituted by a hollow shaft with an opening in the upper part. The low voltage current generated by the alternator is supplied to a high voltage charger, which in turn supplies power to the capacitors of the pulse generator.

the power of the drilling fluid injected by the drilling rig pump located at the surface drives the generator. Thus, the design of the present invention does not require any electrical power transmission system between the surface and the bottom, such as electrical cables, electrically conductive drill pipe, coiled tubing or any other system. Electrical energy is produced at the bottom, thus eliminating the fundamental obstacles presented to the use of drilling systems by means of electrical discharges as presented in the various documents of the prior art. Unlike the prior art literature, this design results in a rotary drilling system by means of the electric discharge of the present invention that is fully compatible with standard drilling procedures. This allows to increase the efficiency of the rock breaking process by combining the mechanical action brought about by the rotation and the effect of the electrical discharge. This allows the drill string to be handled in a conventional manner (raised to the surface and lowered to the bottom) without any impediment to attachment to the drill pipe or the cable within the drill pipe. The continuous rotational movement of the drill string also prevents sticking due to pressure differentials, which is traditionally feared, and reduces the risk that the drill string must be abandoned in the wellbore.

The invention allows the device to be controlled from above ground. Without the additional device of the present invention, the drilling machine cannot allow or prevent the implementation of the electrical operation of the rotary drilling system by electric discharge from the surface. Indeed, controlling only the circulation of mud by the pump allows starting or stopping the operation of the system. However, it is well known in the drilling industry that continuous circulation of mud is a vital necessity for both the safety of the wellbore and the safety of personnel when a drill string is present in the wellbore, even if the drilling tool is not rigorously drilling. This continuous circulation prevents, for wells in the oil and gas sector, the risk of oil or gas blow-outs and any precipitation of rock fragments (cutting chips) and thus the risk of the drill string being blocked. In these conditions, using only the generator without the device according to the invention, a continuous electrical operation of the rotary drilling system by means of electric discharges is brought about, whether or not the circulation of the mud is active. Such rotation is a serious disadvantage for personnel safety, drilling safety and process efficiency.

For personnel safety, it is critical to ensure that the electrical operation of the system is stopped and the capacitor is discharged when the drill string is raised to the surface. It is also desirable to stop the electrical operation of the system when the drill string is under fluid circulation at the "shoe" end of the metal pipe (metal casing). The present invention allows this to be achieved by using a slide switch.

In terms of performance, it is important that the system has as long a life as possible. The reason therefore suggests that the rotary drilling system is triggered by an electric discharge only when the drill string is at the bottom of the borehole, i.e. when the system is used to perform drilling. The invention also allows this to be achieved using a slide switch which will only actuate the device at the bottom of the well if required.

Finally, it is desirable to be able to periodically stop the electrical operation of the system during "mud pulse" transmissions from the MWD to avoid interference between systems. The invention also allows this object to be achieved by using a slide switch.

All these examples (which are not exhaustive) clearly show that it is desirable to have a device for remotely controlling the electrical operation of a rotary drilling system by electrical discharge, and that the remote control is all at hand. Such control is possible from the ground by incorporating an electrical slide switch (9) positioned at various possible locations in the system structure (such switch will be described further below).

In a preferred construction, the electrical slide switch is located at the interface between the hydraulic compartment and the electrical compartment (see fig. 3). The switch acts as a mechanical clutch. The "normal" position of the switch prevents mechanical locking of the hydraulic compartment rotor with the electrical compartment rotor. This provides assurance of the following fact: unless the rig so decides, the system cannot operate. The decision by the drilling rig to operate the system includes: a considerable weight of several tons is applied to the tool, for example between 2t and 15 t; a portion of the drill string is placed in compression. When the drilling machine applies this force, the slide switch is closed, a mechanical lock is established between the rotors of the hydraulic and electric compartments, and the generator then generates an electric current.

In one configuration considered, the electrical slide switch can actuate the system in order to open/close the high voltage power applied to the capacitor.

The "normal" position of the switch prevents high voltage from being supplied to the capacitor. This provides assurance of the fact that: unless the rig so decides, the system cannot operate. The decision by the drilling rig to operate the system includes: a large weight of several tons is applied to the tool; a portion of the drill string is placed in compression. When the drilling machine applies this force, the slider of the switch closes, electrical contact is established, and the system can then be operated.

In another configuration considered, the electrical sliding switch allows to actuate a mechanical locking system between the hydraulic system rotor and the alternator rotor (see fig. 8 and 9 below). The "normal" position of the switch prevents the alternator rotor from rotating. In this position, no current will therefore be generated. As in the case previously described, it provides for the following guarantees of the fact: unless the rig so decides, the system cannot operate. The decision by the drilling rig to operate the system includes: applying a considerable weight of several tons to the tool, in the same principle as the above-mentioned basic principle; a portion of the drill string is placed in compression. When the drilling machine applies this force, the slider of the switch closes, the hydraulic compartment rotor meshes with the alternator rotor, and the system can then be operated.

In another preferred embodiment, the system is equipped with two electrical sliding switches (as shown in fig. 3):

-an upper electric sliding switch (9s) located between the hydraulic and electric compartments of the generator,

-a lower electrical sliding switch (9i) at the electrical drilling tool.

thus, in this configuration, the system is provided with dual security. The upper switch in the normal position guarantees: even if circulation of the drilling fluid is maintained, production from the generator is stopped and no current is supplied to the system. The lower switch in the normal position guarantees: the pulse generator capacitor discharges and cannot be charged.

The electrical slide switch and the downhole generator according to the invention thus give the rotary drilling system by means of electrical discharges the characteristics required by the reliability, safety and drilling regulations, particularly in the oil exploitation sector.

Fig. 4 and 5 depict the pulser and drilling tool (a slider positioned at the electric drilling tool) in a slide open and slide closed position, respectively. In these positions, the pulse generator (6) is connected to a stabilizer (8), the stabilizer (8) being integral with the slide switch (9). The device comprises a ground electrode (11) and a single central or compensation high voltage electrode (12) or a plurality of high voltage electrodes with an insulator (13) between them. The electrodes are not separated by any solid material at their ends at the high pressure chamber (36), the electrodes providing the electrical pulses necessary for drilling. The device also comprises a hole (18) for the circulation of the drilling fluid and a system (19) for mechanical transmission and a capacitor bank (16).

in the open position of fig. 4, the spring (14) in the uncompressed position, the ripple spring (15) in the extended position, the circuit opening/closing system (17) of the circuit for charging and discharging the capacitor on the resistor can be seen, which is in the "normally closed" configuration.

in the closed position of fig. 5, the switch (9a) is shown in the closed position, while the spring is in the compressed (14a) position, the ripple spring is in the compressed position (15a), and the system (17a) for opening/closing the circuit of the circuit for charging and discharging the capacitor (capacitor discharge) on the resistor in the "actuated" configuration. In this configuration of fig. 5, the high-voltage supply circuit to the pulse generator is therefore closed, and the capacitor can be charged. The operational details of the opening/closing capacitor high voltage supply circuit and the capacitor discharge circuit are shown in fig. 10, where the generator (26) is connected to a circuit (27) discharging the capacitance over a "dump" resistor, said discharge circuit further comprising a decoupling capacitor (30) and a contactor (31) actuated by a mechanical transmission system, the circuit being connected to a pulse generator (28) itself connected to a drilling tool (31).

fig. 7 shows mechanical and hydraulic part operational details of the slide switch (the slide positioned at the electric drilling tool) in the slide open and slide closed configurations, respectively. In this fig. 7, the ground electrode (11), the center or compensation high voltage electrode (12), the insulator (13) and the spring (14) in the uncompressed position are shown again, as well as the hole (18) for the circulation of the drilling fluid. Furthermore, the drilling fluid circulation channel (20) inside the insulator (13) is shown as well as the following forces and pressures:

-21: force F1 exerted by spring 14 opening the slider

-22: force F2 generated by pressure [ P2(24) -P1(25) ] resulting from loss of fluid load within the insulator channel (20) and the portion S (23) exerting this pressure

-23: a surface on which a pressure is exerted, said pressure being generated by a fluid load loss [ P2(24) -P1(25) ] in the insulator channel (20)

-24: pressure P1 of drilling fluid upstream of insulator channel (20)

-25: pressure P2 of the drilling fluid downstream of the insulator channel (20).

To enhance the follower action of the slider spring, the vertical channel in the insulator is sized to develop a load loss (Δ P ═ P1-P2), which can be interpreted as the vertical force F2 pointing downward from the top equals the product of the load loss multiplied by the area of the lower slider portion (F2 ═ Δ PxS). This force therefore reinforces the spring force F1 and the force of the suspended weight under the slider.

Thus, when the electric drilling tool is not resting on the bottom of the wellbore and the drilling fluid is circulating, the drilling machine not only has the certainty that the capacitor is no longer powered, but the capacitor is completely discharged. Indeed, the electrical slide switch in the normally open position opens the capacitor charging circuit and also closes the circuit in which the capacitor discharges on the "dump" resistor (see fig. 10). When the tool rests on the bottom of the borehole and a weight and load loss greater than the spring accumulation force is applied to the tool, the slider closes and the drive link actuates the circuit closing/opening system. At this instant, the capacitor charging circuit is closed, the capacitor is no longer connected to the system where the capacitance discharges on the "dump" resistor, and then the rotary drilling by discharge is operable.

Fig. 6 is a view in which the ground electrode (11), the central or compensation high voltage electrode (12), the peripheral high voltage electrode (12a), the insulator (13) and the high voltage chamber (36) formed between the electrodes can be seen.

As described above, the electrical slide switch provides the following three functions:

In a basic principle of the "normal inhibition" type, the rotation of the alternator rotor is passively inhibited and/or the power supply by the alternator to the high-voltage charger and/or to the capacitive power supply circuit of the pulse generator,

Slaved assurance of the circuit closing the discharge of the capacitor on the "dump" resistor with a "normal discharge" type of basic principle

-upon triggering of an active action by the drilling machine from the surface, allowing:

Rotation of the alternator rotor, and/or

-supplying power from the alternator to the high-voltage charger, and/or

-supplying power to the pulse generator capacitor, and

Jointly opening the circuit for discharging the pulse generator capacitor over the resistor (see fig. 10).

The "normally disabled" or "normally open" position of the switch is therefore a guarantee position that guarantees no risk of high voltage and electrical non-operation of the system for rotary drilling by electric discharge.

in one embodiment, the switch is constituted by a slider which is incorporated between the hydraulic compartment (turbine or downhole motor) and the electrical compartment (alternator) of the generator (as shown in figures 3, 7 and 8). The slider is made up of two parts that slide on each other, the two parts having a high stop and a low stop, enabling a stroke from a few centimeters to a few decimeters, for example from 1cm to 20 cm. The slider is designed following a basic principle of the "normal open" type, exerting a strong separating force between the two sliding parts by means of a mechanical spring action of robust construction. The suspended weight below the lower portion of the slider reinforces the spring action, causing the slider to remain in the open position. The upper part of the slider carries a hollow shaft (connected to the rotor of the hydraulic compartment) mounted on bearings to decouple the rotational movement between the slider and the shaft. The lower part of the slider also carries a hollow shaft (connected to the rotor of the electrical compartment) mounted on bearings to decouple the rotational movement between the slider and the shaft. The upper and lower hollow shafts are equipped with a clutch system. One of the hollow shafts also has a seal to ensure continuity of drilling fluid flow regardless of the relative position of the two shafts. When the slider is opened, fluid is free to circulate from the stator/rotor space of the hydraulic compartment to the inside of the rotor of the electrical compartment (alternator) and beyond the electric drilling tool, but the two rotors are not mechanically locked. Thus, despite the ongoing circulation of drilling fluid, the generator does not produce any current since the alternator rotor does not rotate. When the sliders are closed, the clutch system unites the two rotors, thereby allowing the alternator rotors to rotate. Closure of the slide is only possible at a time when the drilling machine compresses a portion of the drill string and applies a weight to the tool that is greater than the spring opening force. From this point on, the system for rotary drilling by electric discharge can then be operated.

Fig. 8 and 9 depict details of the slide switch in the clutch disengaged and engaged positions, respectively (the slider is positioned between the hydraulic and electrical compartments of the generator).

The figure shows the driven upper hollow shaft (36) connected to the generator hydraulic compartment rotor (turbine or downhole motor), the rotational movement being indicated by arrow (38). Circulation of the drilling fluid is identified by arrows (47). The shaft is held within an upper bearing (37).

the figure also shows the lower hollow shaft (42) connected to the generator electrical compartment rotor (alternator), without rotation. The shaft is held in a lower bearing (41). A seal (39) is placed at the connection between the upper shaft (36) and the lower shaft (42). The spring (43) is in an uncompressed position, holding the two shafts apart.

in fig. 9, this position is an engaged position in which the spring is in a compressed position (46), and a mechanical connection (44) is formed between the upper and lower parts of the hollow shaft in the engaged position, which results in a rotational movement of the lower hollow shaft driven by the upper hollow shaft, which movement is indicated by the arrow (45), thus ensuring a mechanical connection.

As described with reference to the figures and in particular fig. 6, the electrical slide switch is composed of three parts:

-a mechanical slider which is movable in relation to the frame,

-a transmission system of the machine,

-a circuit opening/closing system.

The sliding switch system may be incorporated into: (i) the electric drilling tool, or (ii) an interface between the electric drilling tool and the pulser, or (iii) at the pulser, or (iv) between the pulser and the generator, or (v) at the generator, or (vi) above the generator.

The slider is usually linked to a mechanical transmission system which actuates the circuit opening/closing system. In one embodiment, the system consists of one or more rods that slide, depending on the position of the slider in the structure of the system, inside a housing formed within the thickness of the external metal body of the pulse generator and/or generator.

The slider-actuated circuit opening/closing system is particularly concerned with the following circuits:

-a circuit supplying a high voltage charger of the generator; and/or

-a capacitor power circuit from a pulse generator; and/or

-a circuit in which the capacitor discharges over the resistor.

in one embodiment, the slider is positioned at the electric drilling tool. In this configuration, the lower slide portion is constituted by:

-a body carrying a ground electrode,

-an insulator means for insulating the electrical conductor,

-a high voltage electrode system.

The pulse generator is mechanically and electrically connected to the generator. This is a component that creates and delivers very high voltage pulses to the electric boring tool. This may be based on various configurations that start with a boost from the primary voltage.

three structures for boosting the voltage are considered. The first is based on the use of a Marx generator. The second is based on LTD (linear transform driver) technology. The third is based on the Tesla converter technology.

In these three cases, the axis of the pulse generator crosses an axial hollow tube (53), the wall of which is made of insulating material, as shown in figure 13. The hollow tube provides circulation of drilling fluid (52). In the lower part of the pulse generator, the tube is mechanically connected to another hollow tube (54) of the same diameter but with steel wall. The steel pipe receives the high voltage pulse and transmits the high voltage pulse to an electrode system of the electric drilling tool.

Given that the tube is present in the axial section, a preferred structural arrangement is that the components of the pulse generator are arranged in a ring. In the case of a Marx generator (adder of initial V0 voltage using operator order, with initial zero terms and V0 inference), one configuration considered involves stacking the same easily replaceable basic modules (56) within the annulus between the hollow axial tube and the metallic outer sheath. The modules are surrounded by an insulating material (53). Each module is made up of an energy storage device (here a capacitor) and a power switch. The module may have a capacity of between 20nF and 1000nF, preferably between 50nF and 200 nF. The number of modules used determines the desired voltage range of the pulse generator output. The initial voltage applied to the input of the pulse generator is provided by the high voltage charger of the generator. The initial voltage may be between 1kV and 50kV, preferably between 20kV and 40 kV. Generally, the pulse generator output voltage may be between 200kV and 1000kV, preferably between 400kV and 600 kV. The high voltage pulse generation frequency towards the electrode system of the drilling tool may be between 1Hz and 100Hz, preferably between 5Hz and 50 Hz.

in one configuration under consideration, the power switch is a gas discharge tube (49). The electrode is a full ring crown (51). The electrical insulation of the power switch is provided by a gas under pressure, which is maintained or periodically replenished. The annular and contoured shape of the power switch electrodes allows for an increase in the area on each electrode that can be eroded, thus extending their service life.

Electrical isolation between modules is provided by the use of interlocking insulators and compressed seals. The pulse generator output is connected to the electrode system of the drilling tool through an insulated interface, the insulating element of which may be solid, liquid or gas.

In one embodiment, the pulse generator has an upper portion, which is located below the interface with the generator, with a system for opening/closing the circuit that charges and discharges the capacitor (as shown in fig. 3, 4 and 9). The system is actuated by a mechanical transmission system that is actuated by a normally open electrical slide switch. Thus, if the drilling machine is not operated intentionally from the surface, the component ensures that the electrical operation of the system for rotary drilling by electrical discharge will be interrupted and that the operation of the drill string with or without mud circulation can be carried out safely for personnel and materials.

In one embodiment, an electric drilling tool (see, e.g., fig. 3, 4, and 5) includes:

an electrode system, passive and active,

-a body with a stabilizer of standard design.

The electrode system consists of two groups of electrodes separated by insulators:

-one or more high voltage electrodes (33) and (35),

-an insulator (13),

-ground electrodes (11) and (32).

In one embodiment considered, the high voltage electrode system consists of a hollow central shaft connected to a capacitor. The insulator has a vertical channel (20). The drilling fluid circulates within the central shaft and follows two paths:

Into the central shaft of the shaft end, i.e. to the bottom of the electric drilling tool,

-a vertical channel through the insulator (20) perforated in the central shaft of the insulator (18).

The ground electrode is attached to the outer body of the electric drilling tool and is made up of a number of protrusions (32) of robust construction extending horizontally or obliquely, designed to resist the torque and weight on the tool that allows the use of conventional rotary systems. An insulator (13) separates the high voltage electrode system from the ground electrode system, the material of the insulator (13) being ceramic, epoxy or any other insulating component that is capable of withstanding the temperatures and mechanical forces experienced under drilling conditions.

A special feature of the electric drilling tool according to the invention is the arrangement of the electrodes relative to the tool substrate. Indeed, the prior art documents show the fixation of the electrodes within the matrix, thereby inducing solid material to be present between the high voltage electrode and the ground electrode, close to the ends of the electrodes. Other documents of the prior art do not give details in this respect. Indeed, the solid material makes it an insulator, which is at risk of being destroyed if it is present between the electrodes in the part of the high voltage component that is too close to the grounded component. When drilling is carried out, a small part of the arc may take a straight line between the electrodes, although most of the arc penetrates the rock. This tendency will be even stronger when there is not so good physical contact between the rock and the electrode. Furthermore, when the electric drilling tool is lifted off the bottom of the borehole and the system is assumed to be still operating (which is not the case in the present invention due to the electrical slide switch), all arcs will take a straight line between the electrodes, thereby destroying solid material on the path. The basic principle of construction of the electrode systems known from the prior art is therefore not feasible.

To solve this problem, the terminal portion of the electric drilling tool of the present patent comprises an internal chamber devoid of any solid material other than the electrode. The chamber is bounded upwardly by the lower portion of the insulator and laterally by the frame of the ground portion. A high voltage electrode passes through the chamber. This design ensures that: once the distance between the ground and high voltage parts is greatly reduced to a value less than the value of the two parts at the separation insulator, any electric arc generated within the chamber has no consequence on the integrity of the electric drilling tool.

the result of this design is: the configuration of the insulator on the one hand and the high voltage electrode on the other hand gives them mechanical strength with respect to the compressive forces and torques to which the insulator and the high voltage electrode are subjected during rotary drilling.

in one embodiment, the insulator provides the following two functions:

By keeping the distance between the high-voltage shaft and the ground portion substantially greater than the distance (34) separating the end of the high-voltage electrode system and the end of the ground electrode system, and also by avoiding the phenomenon of uncontrolled propagation of current lines along the contact surface between the two environments of different resistivity, which can lead to the formation of electric arcs, i.e. what is called the "tracking" phenomenon, thereby providing electrical insulation between the high-voltage shaft and the ground portion,

-mechanically connecting the body of the electric drilling tool to the grounded and high voltage electrode systems for both rotational and axial movements to maintain the space between the ends of the two electrode systems at a constant value (34).

Several geometrical properties of the electrode system may be considered:

-a single high voltage electrode is positioned on the axis of the electric drilling tool, while the peripheral ground electrode is of constant size;

-a single high voltage electrode (33) is centrally located but offset with respect to the axis of the electric drilling tool, while the peripheral ground electrode (32) is variably sized and adjusted to maintain a constant space (34) between the end of the ground electrode and the high voltage electrode (as depicted in fig. 11);

-the high voltage electrode system comprises a central compensation electrode (33) and a peripheral electrode (35) interposed between the ground electrodes (32), the space (34) between the ends of the ground electrodes and the high voltage electrode being maintained at a constant value (as depicted in figure 12).

the offset high pressure device is beneficial in avoiding insufficient fragmentation rate in the central part of the bore. The combined effect of the offset position and rotation thus ensures that no surface of the borehole can escape the presence of the arc. Furthermore, such an asymmetric configuration allows for the ground electrode to be arranged in varying sizes. Some ground electrodes are large in size: which are opposite the center electrode with respect to the axis of the borehole. Other ground electrodes are small in size and they are ground electrodes located on the same side of the axis of the borehole as the center electrode.

The largest electrode is one whose dimensions are compatible with the arrangement on the electrode insert, for example, of Polycrystalline Diamond Compound (PDC) (61) type, or tungsten carbide type, or other types of hard and wear-resistant materials, without risking their being swept away by the arc because they are sufficiently far away from the end of the electrode where the arc forms. The presence of these inserts on the front and on the sides of these electrodes thus equipped allows therefore to intensify the effect of the electric arc by mechanical action and to protect the electrodes from premature wear caused by rotation. It is also possible to equip the electrode end with an impregnated matrix (62) comprising powders or microparticles of diamond or any material intimately mixed with a metal matrix to protect the electrode from premature wear caused by rotation. This embodiment is shown in fig. 15.

Furthermore, the presence of the small size electrodes allows the formation of an arc very close to the periphery of the wellbore, thereby increasing the coverage of the arc on the surface of the wellbore.

In another embodiment, when the high voltage electrode system consists of a single central electrode located in the axis of the electric drilling tool, the insulator provides an "electrical insulation" function, mechanically connecting the ground connection part with the high voltage part from an axial point of view, but allowing the rotational decoupling between the two parts. Such a construction thus avoids premature wear of the end of the high voltage electrode.

in another embodiment, the insulator only provides an "electrical isolation" function and allows for a mechanical decoupling between the ground and high voltage parts from an axial and rotational point of view. Such a configuration therefore not only avoids premature wear of the high voltage electrode tip, but also maintains continuous contact between the electrode and ground.

In one embodiment, as shown in fig. 14, a system for rotary drilling by electric discharge is electrically insulated from the upper portion of the drill string by an insulated connector. The connector is comprised of a metallic upper portion (58) and a metallic lower portion (57), the two portions being separated by an insulator (60). The geometry of the part nesting ensures the absorption of axial as well as torsional stresses. Thus, the connector may be positioned just above the generator or higher, depending on the configuration of the drill string. The connector facilitates two potential functions:

-to facilitate the safety of the personnel on the ground,

Avoiding potential interference with MWD and LWD type electronics.