Method and apparatus for drilling a borehole in a rock formation

Abstract

A method for laser drilling with a laser beam generator located outside the borehole, in which liquid nitrogen is supplied to the laser boring head via a boring rod, which liquid nitrogen is converted into a gaseous state in the region of the boring head and is divided into a protective gas flow (18) passing through a laser guide tube (19) in a direction towards the surface and a conveying gas flow (15) carrying away the detached rock material through an annular space. The heating gas flow (10) is heated by an electric heating device (11) and directed towards the bottom of the hole where the laser beam is applied.

Description

[Technical field]

[0001] The present invention relates to a method for drilling a borehole in a rock formation by irradiating a laser beam at the bottom of the borehole, the laser beam being generated by a laser beam generator located outside the borehole and being fed by suitable auxiliary means to a laser boring head located at the bottom of the borehole and connected to a boring rod, the laser boring head being fed with nitrogen via the boring rod, the nitrogen being fed in the region of the laser boring head by: a partial flow serving as a protective gas flow protecting the passing laser beam from interfering suspended matter; - another partial flow acting as a carrier gas flow to carry the rock material dislodged at the bottom of the hole out of the borehole through the remaining annular space between the drill rod and the hole wall; The present invention relates to a method and apparatus for dividing a [Background technology]

[0002] Such an apparatus is known, for example, from DE 10 200 43 336. In this known boring method of the above-mentioned type, a flexible tube, for example a helical tube, is used as an auxiliary means for supplying the laser beam and for supplying the required nitrogen as protective gas and carrier gas, in the inner chamber of which a glass fiber cable is arranged for transmitting the laser beam, in which there is still enough free space left in the tube for a sufficient amount of nitrogen to pass through. The protective gas flow and the laser beam leave together through an opening on the underside of the laser boring head facing the bottom of the hole and strike the bottom of the hole together. The energy of the laser beam striking the bottom of the hole ablates the rock material exposed at the bottom of the hole, and depending on the rock material, by melting, vaporization and / or spalling. The thermally dislodged rock material is then displaced by the protective gas flow impinging simultaneously on the bottom of the hole towards the edge of the bottom of the hole, where it is picked up by a conveying gas stream oriented in a discharge direction, which carries the dislodged material from the bottom of the hole out of the borehole via the annular space present between the drilling rod and the hole wall.

[0003] Such methods and apparatus have a series of conflicting requirements that create problems in practical implementation.

[0004] The thermal ablation of rock at the bottom of the hole used in this method naturally requires a large amount of energy, which is essentially provided by the laser beam. Corresponding experiments have shown that in normal rock formations, the thermal ablation of rock material at the bottom of the hole by means of a laser beam requires an energy of 400 W / cm 2It has been found that a power density exceeding 500 kW is required. To achieve this power density, in prior art devices the laser beam must be correspondingly focused in the impact area at the bottom of the hole and guided successively across the bottom of the hole. This requires complex mechanisms and / or supporting boring tools integrated in the laser boring head if it is desired to achieve a sufficient drilling progress. It would be better, however, if the entire bottom of the hole could be irradiated simultaneously in a sufficiently focused manner, for example by means of an expander lens in the laser boring head. However, for this, a laser beam with a power of more than 500 kW, preferably 600 kW to 700 kW, is required for normal borehole diameters.

[0005] However, such a high power laser beam can no longer be easily transmitted through a glass fiber cable, especially if the glass fiber cable has to be 2000m to 10000m long based on the borehole depth to be reached. That is, the glass fiber cable has a relatively large attenuation factor, so that if the glass fiber cable is of such a length, the delivered laser beam no longer reaches the laser boring head with sufficient intensity.

[0006] Furthermore, the required increase in the power of the laser beam causes thermal problems, since the energy released in the form of heat at the bottom of the hole, which is brought with the laser beam, can lead to unacceptable overheating of the laser boring head and the boring rod. The supply of gaseous nitrogen in the protective gas flow and the carrier gas flow is insufficient to a sufficient extent to dissipate the excess heat, taking into account such a high power of the laser beam. Furthermore, the intensive supply of a cold protective gas flow to the bottom of the hole can cause thermal short circuits in the area of ​​the bottom of the hole, which can interfere with the thermal ablation process of the rock material at the bottom of the hole. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Patent Application Publication No. 2010 / 0044102 Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore an object of the present invention to improve a method of the type mentioned at the beginning in such a way that even in the case of very deep boreholes, a sufficiently rapid drilling progress is possible without harmful overheating occurring in the laser boring head or the boring rod. [Means for solving the problem]

[0009] In order to achieve this object, the present invention proceeds from a method of the type mentioned at the beginning, - supplying the laser beam to the laser boring head via a laser guide tube which extends over the length of the boring rod and whose free cross section is circulated by a protective gas flow, - feeding nitrogen in a liquid agglomerated state via the boring rod to the laser boring head and transferring it to a gaseous agglomerated state in the region of the laser boring head; - It is provided that from the supplied nitrogen, another partial flow serving as a heating gas flow is additionally branched off, which partial flow is heated by an electric heating device arranged corresponding to the laser boring head and directed towards the bottom of the hole where the laser beam is irradiated.

[0010] By using a laser guide tube, which is circulated by a protective gas flow, instead of the glass fiber cable as is customary according to the prior art, as defined by the invention, it is easily possible to transmit the laser beam at very high power and almost without losses over the entire length of the boring rod; clean gaseous nitrogen, for example, has a very low attenuation effect. For the deflection and, if necessary, the correction of the beam direction of the laser beam in the shape of the laser guide tube, it is easily possible to arrange suitable lens and / or mirror systems at suitable intervals in the guide tube. These lens and / or mirror systems must of course not interrupt the protective gas flow passing through them.

[0011] Furthermore, in the method according to the invention, nitrogen is supplied to the laser boring head in a liquid condensed state and is finally transferred to a gaseous condensed state in the region of the laser head, thereby providing a sufficient amount of cooling medium for cooling the laser boring head, the protective gas flow, the carrier gas flow and the boring rod, i.e., the transfer of the condensed state is highly endothermic and significantly increases the volume to be supplied, so that cold nitrogen gas is provided in a sufficient amount in the region of the laser boring head and can be distributed as required to avoid overheating phenomena.

[0012] The above-mentioned thermal short circuit is finally avoided by the electrically preheated heating gas flow directed at the bottom of the hole, which is finally defined according to the invention. As a result, it is possible to easily intensify this heating gas flow, which supports the ablation operation of the laser beam and at the same time the ejection of the rock material ablated at the bottom of the hole in the direction of the conveying gas flow. Preferably, this heating gas flow is instead given a temperature close to the melting temperature of the rock exposed in each case.

[0013] Another problem with the method according to the invention is that the molten or vaporized rock material contained in the ascending conveying gas stream must be cooled below the solidification temperature of the rock before it possibly enters the annular space between the boring rod and the hole wall. This cooling prevents the rock material from depositing on the boring rod and / or the hole wall. For this purpose, it is further proposed to additionally use liquid nitrogen as conveying gas, which is injected in the area of ​​the laser boring head into the conveying gas stream flowing back from the bottom of the hole and containing the rock material detached from the bottom of the hole, and in this area to cool the conveying gas stream and the rock material present in the conveying gas stream while transferring it to a gaseous condensed state. The liquid nitrogen used for this purpose is branched off in the laser boring head from the liquid nitrogen stream supplied to the laser boring head via the boring rod.

[0014] It is furthermore preferred to provide that from the nitrogen supplied to the laser boring head, a further partial flow, which acts as a cooling gas flow, is branched off and led out of the borehole via the boring rod, thereby cooling the boring rod from the inside, so that additionally, heat is not unnecessarily supplied from the conveying gas flow to the inner space of the boring rod.

[0015] Finally, the method according to the invention further provides for branching off another partial flow from the nitrogen supplied to the laser boring head, which serves as a cleaning gas flow, and which keeps the laser beam outlet opening of the laser boring head facing the bottom hole and covered by the expander lens clean, thereby preventing the light-transmitting coated laser beam outlet opening from being contaminated by floating material rising from the bottom hole, consisting of detached rock material, and thus becoming less transparent to the laser beam.

[0016] The subject of the invention is also an apparatus for carrying out the above-mentioned method, which is characterized primarily by the special configuration of the boring rod, which comprises: - a laser guide tube through which a protective gas flow passes for the laser beam to pass; - a double tube concentrically and radially surrounding the laser guide tube, the annular space of the double tube being circulated with liquid nitrogen; - an insulating tube concentrically and radially surrounding the double tube; - an outer protective tube surrounding the insulating tube concentrically and radially spaced therefrom; It has - The annular space surrounding the double tube is evacuated; - the annular space between the outer protective tube and the insulating tube is connected to the cooling gas flow returning from the laser boring head; - One or more tubes surrounded by an outer protective tube contain electrical conductors for transmitting electrical energy and electrical signals to the laser boring head.

[0017] Such a boring rod allows, in a compact construction, a sufficiently unattenuated passage of a high-power laser beam through the laser guide tube, a sufficiently vacuum-insulated transmission of liquid nitrogen through the annular space of the double tube, a good insulation of the entire boring rod against heat from the transport flow, and the transmission of electrical energy and electrical signals to the laser boring head.

[0018] It is further preferably specified that the outer protective tube is made of steel and the tube arranged inside the protective tube is made of carbon fiber reinforced plastic (CFK). The outer protective tube made of steel gives the entire boring rod the necessary stability and insensitivity to unintentional overheating from the outside. The material used for the inner tube is distinguished by a low weight and extremely high strength, and is also well thermally insulating and sufficiently electrically insulating.

[0019] Furthermore, the present invention also provides an apparatus for carrying out the method, the laser boring head having a housing, the housing cover of which is attached to an outer protective tube of the boring rod, the housing being: a passage for the laser beam, which extends through the housing and is connected to the laser guide tube of the boring rod, the outlet opening of which is optically transparently covered by an expander lens in the area of ​​the housing bottom; - a device arranged in the housing interior and connected to the annular space of the double tube of the drilling rod for conveying and / or vaporizing the incoming liquid nitrogen and for storing and dividing the gaseous nitrogen into different defined partial flows; - a conveying jet nozzle arranged on the housing periphery and extending obliquely in the flow direction of the conveying gas flow for injecting liquid nitrogen into the conveying gas flow; - a heated jet nozzle for a heated gas flow, arranged at the bottom of the housing and directed towards the bottom of the hole; - an electric heating device for the heating gas flow, the heating device being arranged in the housing interior; - with solenoid valves and volumetric flow regulators for control and regulation of all nitrogen partial flows The present invention is characterized by further comprising:

[0020] With such a laser drilling head, it is possible to deliver a laser beam arriving through the laser guide tube of the drilling rod to the bottom of the hole without sufficient attenuation, to vaporize liquid nitrogen delivered through the double tube of the drilling rod, and to control the volume flow rate and divide it into various partial flows.

[0021] It is furthermore advantageous if a partial flow acting as a cooling gas flow passes through the housing interior and is connected to the annular space between the protective tube and the insulating tube on the outside of the boring rod, so that the cooling gas flow responsible for cooling the housing simultaneously obtains the function of keeping the outer surface of the boring rod sufficiently cooled.

[0022] When using the device according to the invention, there is a risk that rock particles rising from the bottom of the hole will contaminate the expander lens arranged in the exit area of ​​the laser beam. To prevent this, it is further provided that cleaning nozzles for a partial flow acting as a cleaning gas flow are arranged in the housing bottom, which run parallel to the underside of the housing bottom and are directed towards the expander lens covering the passage opening for the laser beam.

[0023] In order to supply the laser guide tube with a clean protective gas flow sufficiently and over its entire length, including the housing of the laser boring head, it is further provided that in the housing of the laser boring head, the through passage for the laser beam is provided with an inlet opening for a partial flow that serves as the protective gas flow.

[0024] Finally, it is provided that, in the passageway for the laser beam and / or inside the laser guide tube, spaced apart holding devices for holding the lens and / or mirror system for deflecting the laser beam are arranged, which are made gas-permeable for the flow of protective gas, by means of such devices, it is possible to reorient and / or focus the laser beam as required in the event that the borehole and the corresponding boring rod deviate from a straight shape.

[0025] An embodiment of the present invention will now be described with reference to the accompanying drawings. [Brief description of the drawings]

[0026] [Figure 1] FIG. 2 is a schematic longitudinal section view of a laser boring head attached to a boring rod in a working position above the bottom of a hole; [Diagram 2] FIG. 2 is a cross-sectional view showing a boring rod. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] In the drawings, the laser boring head is generally indicated by the reference numeral 1 and the boring rod supporting the laser boring head 1 is generally indicated by the reference numeral 2. The laser boring head 1 and the boring rod 2 are located in a borehole 4 drilled in a rock formation 3, having a hole wall 4a and a hole bottom 4b.

[0028] The laser boring head 1, which is held in the working position at a slight distance above the bottom of the hole 4b, has a substantially cylindrical housing 5, the housing cover 5a of which is connected to the boring rod 2.

[0029] The housing 5 further has a housing bottom 5b arranged at a distance from the bottom of the hole 4b, which is provided in the center with a passage opening 6 for a laser beam 7 fed via the boring rod 2 and transmitted through the housing 5. In the passage opening 6 an expander lens 8 is located, which expands the incoming laser beam 7 in such a way that the laser beam 7 is irradiated over the entire bottom of the hole 4b.

[0030] Furthermore, a heating jet nozzle 9 is located in the housing bottom 5b, which generates a heating gas flow 10 directed towards the bottom of the hole 4b, and which is supplied with heating gas from an electric heating device 11 arranged in the interior of the housing 5.

[0031] Further, cleaning nozzles 12 are positioned in the housing bottom 5b, and these cleaning nozzles 12 are adjusted parallel to the lower surface of the housing bottom 5b in a direction toward the centrally located expander lens 8, and the cleaning nozzles 12 are supplied with clean gaseous nitrogen from a nitrogen collection container 13 located inside the housing 5 as a cleaning gas flow 14 for keeping the expander lens 8 clean.

[0032] Furthermore, the housing 5 of the laser boring head 1 has a housing peripheral wall 5c which leaves an annular space in relation to the borehole wall 4a for the passage of a conveying gas flow 15 containing the detached rock material rising from the bottom of the hole 4b. This conveying gas flow 15 originates from the edge region of the bottom of the hole 4b where the heating gas flow 10 is applied and carries the rock material detached from the bottom of the hole out of the borehole 4.

[0033] To support this ascending conveying gas flow 15, conveying jet nozzles 16 and 17 are arranged in the housing circumferential wall 5c of the housing 5 of the laser boring head 1, which conveying jet nozzles 16, 17 run obliquely in the direction of the conveying gas flow 15 and which can be supplied with liquid nitrogen and / or gaseous nitrogen from inside the housing 5. If liquid nitrogen is provided via the conveying jet nozzle 16, this liquid nitrogen makes a particularly strong contribution to the cooling of the rock material contained in the conveying gas flow 15.

[0034] In order to be able to supply the laser beam 7 to the laser boring head 1 as unattenuated as possible and also to be able to supply the laser boring head 1 with a sufficient amount of nitrogen, a specially designed boring rod 2 is provided, which will be described in more detail below.

[0035] The boring rod 2 comprises a number of tubes arranged concentrically with respect to one another, i.e. an inner laser guide tube 19 for passing the laser beam 7, which is circulated by a protective gas flow 18, which consists of clean nitrogen gas, is fed into the inside of the laser guide tube 19 above the passage opening 6 in the housing 5 of the laser boring head 1 and through an inlet opening 20 located inside the housing 5, a double tube 21 concentrically and radially surrounding the laser guide tube 19, the annular space 21a of which is circulated by liquid nitrogen; an insulating tube 22 surrounding the double tube 21 concentrically and radially spaced apart from the double tube 21; an outer protective tube 23 surrounding the insulating tube 22 concentrically and radially spaced apart from it; It has.

[0036] The annular space surrounding the double tube 21 towards the laser guide tube 19 and towards the insulating tube 22 is evacuated, so that the liquid nitrogen flowing through the annular space of the double tube 21 can be kept sufficiently insulated.

[0037] The annular space between the outer protective tube 23 and the insulating tube 22 is connected to a cooling gas flow 24 returning from the housing 5 of the laser boring head 1, which provides sufficient cooling of the outside of the boring rod 2.

[0038] The outer protective tube 23 is made of steel, which provides good stability and load-bearing capacity to the entire boring rod 1. On the other hand, all the tubes located inside the protective tube 23, i.e., the laser guide tube 19, the double tube 21 and the insulating tube 22, are made of carbon fiber reinforced plastic (CFK).

[0039] Additionally, one or more of the multiple tubes surrounded by the outer protective tube 23 are provided with electrical conductors (not shown in detail) for transmitting electrical energy and electrical signals in the direction of the laser boring head 1.

[0040] To simplify the handling of the boring rod 2, the boring rod 2 is divided into several longitudinal sections, the respective ends of which can be connected to one another by means of screwable countersunk joints 25, 26. In the region of these countersunk joints 25, 26, adjacent sections of the laser guide tube 19, the annular space of the double tube 21 and the annular space between the outer protective tube 23 and the insulating tube 22 are aligned and connected to one another in a pressure-tight manner. Furthermore, in the region of these countersunk joints 25, 26, adjacent sections of the electrical conductor are conductively connected to one another. In contrast, the annular spaces present in the individual sections of the boring rod 2, which are evacuated to insulate the double tube 21, are each closed individually in a pressure-tight manner and are not connected to one another.

[0041] Finally, in the passage opening 6 for the laser beam 7 and / or inside the laser guide tube 19, a number of holding devices 27 for holding a lens system or mirror system for deflecting the laser beam 7 are arranged at a distance from one another, which holding devices are made transparent to the protective gas flow 18, i.e. the edges of the holding devices are provided with corresponding through holes.

[0042] In the housing 5 of the laser boring head 1, a number of solenoid valves 28 and volume flow regulators 29 are located, which can be driven and controlled via a signal conductor contained in the boring rod 2, and distribute the liquid nitrogen supplied to the housing 5 via the double pipe 21 to the conveying jet nozzles 16, 17, the collecting vessel 13 for the gaseous nitrogen, the heating device 11 for the heating gas flow 10, and the housing inner space as required. Here, the control and adjustment are performed in such a way that the system maintains a thermodynamic equilibrium despite the energy supplied by the laser beam.

[0043] The system shown in the drawing works in principle as follows.

[0044] A laser beam 7 having an output of 500kW to 700kW is supplied from a high-power laser generator located outside the borehole 4 into the laser guide tube 19 and is then fed to the laser boring head 1. At the same time, a protective gas flow 18 made of clean nitrogen gas is supplied from below into the laser guide tube 19, so that the laser beam is hardly attenuated on its way to the laser boring head 1. Next, in the laser boring head 1, the laser beam 7 is expanded by an expander lens 8 so as to cover the entire bottom of the hole 4b.

[0045] At the same time as the laser beam 7 is expanded, a heated gas flow 10 is fed to the bottom of the hole 4b. The heated gas flow 10 is previously brought to a temperature close to or even above the melting temperature of the rock exposed at the bottom of the hole 4b by a heater 11. Under the action of the laser beam 7 and the heated gas flow 10, rock material is removed at the surface of the bottom of the hole 4b by melting, vaporizing or fragmenting and is pushed by the heated gas flow 10 towards the outer edge of the bottom of the hole 4b.

[0046] In the process, in this edge region an upwardly directed conveying gas flow 15 containing the removed rock material is formed, which conveying gas flow 15 passes upwards through the annular space between the housing peripheral wall 5c and the wellbore wall 4a.

[0047] Liquid and / or gaseous nitrogen is further injected into the rising conveying gas stream using conveying jet nozzles 16 and 17, thereby cooling and simultaneously strengthening the conveying gas stream 15. The conveying gas stream 15 containing the rock material then exits the borehole 4 via the annular space between the drilling rod 2 and the hole wall 4a. [Explanation of symbols]

[0048] 1 Laser boring head 2 Boring Rod 3 rock layers 4 Boreholes 4a Pit wall 4b Bottom of the mine 5. Housing 5a Housing cover 5b Bottom of housing 5c Housing periphery 6 Passage opening 7 Laser Beam 8 Expander Lens 9 Heated Jet Nozzle 10. Heated Gas Stream 11 Heating device 12 Cleaning nozzle 13 Nitrogen gas collection container 14 Cleaning gas flow 15 Carrier gas flow 16 Conveying jet nozzle 17 Conveying jet nozzle 18 Protective gas flow 19 Laser guide tube 20 Inflow opening 21 Double pipe 22 Insulating tube 23 Protection tube 24 Cooling gas flow 25 / 26 Spigot joint 27 Holding device

Claims

1. A method for drilling a borehole (4) in a rock formation (3) by irradiating a laser beam (7) to the bottom of the hole (4b), the laser beam (7) being generated by a laser beam generator located outside the borehole and being supplied by suitable auxiliary means to a laser boring head (1) located at the bottom of the hole (4b) and connected to a boring rod (2), the laser beam (7) being supplied to the laser boring head (1) via the boring rod (2) with nitrogen, the nitrogen being: a partial flow serving as a protective gas flow (18) for protecting the passing laser beam (7) from interfering suspended matter; another partial flow acting as a conveying gas flow (15) carrying the detached rock material at the bottom of the hole (4b) out of the borehole (4) through the annular space remaining between the drilling rod (2) and the hole wall (4a); In a method of dividing The laser beam (7) is fed to the laser boring head (1) via a laser guide tube (19) which extends over the length of the boring rod and whose free cross section is circulated by the protective gas flow (18), The nitrogen is supplied to the laser boring head (1) in a liquid condensed state via the boring rod (2) and is transferred to a gaseous condensed state in the region of the laser boring head (1); and Another partial flow, which serves as a heating gas flow (10), is additionally branched off from the supplied nitrogen, and this other partial flow is heated by an electric heating device (11) arranged corresponding to the laser boring head (1) and directed to the bottom of the hole (4b) where the laser beam (7) is irradiated. A method comprising:

2. 2. The method according to claim 1, further comprising the step of: additionally using liquid nitrogen as a carrier gas, which is injected in the region of the laser boring head (1) into the conveying gas flow (15) flowing back from the bottom of the hole and containing the rock material detached from the bottom of the hole, and while cooling the conveying gas flow (15) and the rock material present in the conveying gas flow in the region of the laser boring head (1), transitioning them into the gaseous condensed state.

3. 3. The method according to claim 1, further comprising branching off a further partial flow, which acts as a cooling gas flow (24), from the nitrogen supplied to the laser boring head (1) and leading this further partial flow out of the borehole (4) via the boring rod (2), thereby cooling the boring rod (2) from the inside.

4. 4. The method according to claim 1, further comprising branching off a further partial flow from the nitrogen supplied to the laser boring head (1) which acts as a cleaning gas flow (14), the further partial flow keeping a laser beam exit opening of the laser boring head (1) facing the bottom of the hole (4b) clean.

5. 2. An apparatus for carrying out the method according to claim 1, characterized in that the boring rod (2) a laser guide tube (19) for passing said laser beam (7) and circulated by said protective gas flow (18); a double tube (21) surrounding said laser guide tube (19) concentrically and radially spaced apart, the annular space of said double tube (21) being circulated by liquid nitrogen; an insulating tube (22) surrounding said double tube (21) concentrically and radially spaced apart; an outer protective tube (23) surrounding said insulating tube (22) concentrically and at a radial distance therefrom; having - the annular space surrounding the double tube (21) is evacuated, the annular space between the outer protective tube (23) and the insulating tube (22) is connected to a cooling gas flow (24) returning from the laser boring head (1); - one or more tubes surrounded by the outer protective tube (23) are provided with electrical conductors for transmitting electrical energy and electrical signals to the laser boring head (1); An apparatus comprising:

6. 6. The device according to claim 5, characterized in that the outer protective tube (23) is made of steel and the tube arranged inside the protective tube (23) is made of carbon fiber reinforced plastic (CFK).

7. The boring rod (2) is divided into a number of longitudinal sections, the respective ends of which are connected to one another by means of screwable countersunk joints (25, 26), in the region of the countersunk joints (25, 26): - adjacent sections of the laser guide tube (19), the annular space of the double tube (21) and the annular space between the outer protective tube (23) and the insulating tube (22) are aligned with each other and pressure-tightly joined; adjacent sections of the electrical conductor are conductively connected to one another, - the successive sections of the evacuated annular space surrounding the double tube (21) are closed off from one another in a pressure-tight manner without any connections; 7. Apparatus according to claim 5 or 6, characterized in that

8. The laser boring head (1) has a housing (5), a housing cover (5a) of the housing (5) is attached to the outer protective tube (23) of the boring rod (2), and the housing (5) is a passage (6) for the laser beam, which extends through the housing (5) and connects to the laser guide tube (19) of the boring rod (2), the outlet opening of which is optically transparently covered by an expander lens (8) in the region of the housing bottom (5b); - a device arranged in the housing interior and connected to the annular space of the double tube (21) of the boring rod (2), for conveying and / or vaporizing the incoming liquid nitrogen and for storing and dividing the gaseous nitrogen into different defined partial flows; - conveying jet nozzles (16, 17) arranged on the housing periphery (5c) and extending obliquely in the flow direction of the conveying gas stream for injecting liquid and / or gaseous nitrogen into the conveying gas stream (15); a heated jet nozzle (9) for the heated gas flow (10) arranged in the housing bottom (5b) and directed towards the bottom of the hole (4b); an electric heating device (11) for the heating gas flow (10) arranged within the housing interior; - solenoid valves and volumetric flow regulators (28, 29) for control and regulation of all nitrogen partial flows; 8. The device according to claim 5, further comprising:

9. 9. The device according to claim 8, characterized in that the partial flow acting as cooling gas flow (24) flows through the housing interior, which is connected to the annular space between the outer protective tube (23) and the insulating tube (22) of the boring rod (2).

10. 9. The device according to claim 8, characterized in that in the housing bottom (5b) a cleaning nozzle (12) for the partial flow (14) serving as a cleaning gas flow (14) is arranged, which runs parallel to the underside of the housing bottom (5b) and is directed towards an expander lens (8) covering the passage opening (6) for the laser beam.

11. 9. The device according to claim 8, characterized in that in the housing (5) of the laser boring head, the passage opening (6) for the laser beam (7) is provided with an inlet opening (20) for the partial flow serving as a protective gas flow (18).

12. 12. The device according to claim 5, wherein spaced apart holding devices (27) for holding a lens and / or mirror system deflecting the laser beam (7) are arranged inside the passage opening (6) for the laser beam (7) and / or inside the laser guide tube (19), the holding devices (27) being designed to be gas-permeable to the protective gas flow (18).

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