METHOD AND DEVICE FOR LASER DRILLING

Abstract

There is a method for drilling a borehole in a rock formation by bombarding the borehole bottom with a laser beam, which is generated by a laser-beam generator situated outside the borehole and is guided by means of suitable auxiliary devices to a laser-drilling head situated at the borehole bottom. The drilling head is coupled with a drill rod, wherein nitrogen, supplied to the laser-drilling head via the drill rod, is split into a partial stream serving as protective gas, which protects the transmitted laser beam from interfering suspended particles. There is a further partial stream, serving as a conveying-gas stream, which transports the rock material detached from the borehole bottom out of the borehole via an annular space remaining between drill rod and borehole wall. The laser beam is guided to a laser drilling head by extending through a laser guide tube.

Claims

1. A method for drilling a borehole (4) in a rock formation (3) by bombarding the borehole bottom (4b) with a laser beam (7), which is generated by a laser-beam generator situated outside the borehole and is guided by means of suitable auxiliary devices to a laser-drilling head (1) situated at the borehole bottom (4b) and coupled with a drill rod (2), wherein nitrogen, supplied to the laser-drilling head (1) via the drill rod (2), is split into a partial stream serving as protective gas (18), which protects the transmitted laser beam (7) from interfering suspended particles, and a further partial stream, serving as a conveying-gas stream (15), which transports the rock material detached at the borehole bottom (4b) out of the borehole (4) via an annular space remaining between drill rod (2) and borehole wall (4a), wherein the laser beam (7) is guided to the laser-drilling head (1) via, extending over the length of the drill rod, a laser-guide tube (19), through the open cross section of which the protective-gas stream (18) is flowing, wherein the nitrogen is supplied to the laser-drilling head (1) via the drill rod (2) in liquid state of matter and in the region of the laser-drilling head (1) is changed into the gaseous state of matter, and wherein a further partial stream serving as heating-gas stream (10) is additionally branched off from the supplied nitrogen, and is heated by means of an electrical heating device (11) associated with the laser-drilling head (1) and is directed toward the borehole bottom (b) being bombarded by the laser beam (7).

2. The method according to claim 1, wherein liquid nitrogen is additionally used as conveying gas, wherein it is injected in the region of the laser-drilling head (1) into the conveying-gas stream (15) flowing back from the borehole bottom and loaded with rock material detached from the borehole bottom, and is changed therein into the gaseous state of matter, with cooling of the conveying-gas stream (15) and the rock material contained in it.

3. The method according to claim 1, wherein a further partial stream serving as cooling-gas stream (24), which is passed via the drill rod (2) out of the borehole (4) and in the process cools the drill rod (2) from inside, is branched off from the nitrogen being supplied to the laser-drilling head (1).

4. The method according to claim 1, wherein a further partial stream, which keeps clean the laser-beam outlet aperture, turned toward the borehole bottom (4b), of the laser-drilling head (1), is branched off from the nitrogen supplied to the laser-drilling head (1) to serve as a cleaning-gas stream (14).

5. An apparatus for performance of the method according to claim 1, wherein the drill rod (2) has: a laser-guide tube (19), through which the protective-gas stream (18) flows, for the transmission of the laser beam (7), concentrically surrounding the laser-guide tube (19) with radial clearance, a double tube, (21), through the annular space of which liquid nitrogen flows, an insulating tube (22), concentrically surrounding the double tube (21) with radial clearance, and an outer protective tube (23) concentrically surrounding the insulating tube (22) with radial clearance, wherein the annular spaces surrounding the double tube (21) are evacuated, the annular space between the outer protective tube (23) and the insulating tube (22) is connected to the cooling-gas stream (24) returning from the laser-drilling head (1) and one or more of the tubes surrounded by the outer protective tube (23) is or are equipped with electrical conductors for transmission of electrical energy and electrical signals to the laser-drilling head (1).

6. The apparatus according to claim 5, wherein the outer protective tube (23) consists of steel and the tubes disposed in the interior of the protective tube (23) consist of carbon-fiber-reinforced plastic (CFP).

7. The apparatus according to claim 5, wherein the drill rod (2) is subdivided into longitudinal portions, which are respectively joined with one another at their ends by threaded socket-and-spigot joints (25, 26), wherein, in the region of these socket-and-spigot joints (25, 26), the mutually adjoining portions of the laser-guide tube (19) as well as of the annular space of the double tube (21) and of the annular space between the outer protective tube (23) and the insulating tube (22) are joined in aligned and pressure-tight manner with one another, the mutually adjoining portions of the electrical conductors are connected with one another in electrically conducting manner, and the successive portions of the evacuated annular spaces surrounding the double tube (21) are closed in pressure-tight manner without joint with one another.

8. The apparatus according to claim 5, wherein the laser-drilling head (1) has a housing (5), the housing top (5a) of which is fastened to the outer protective tube (23) of the drill rod (2), wherein the housing (5) is further equipped with: for the laser beam, extending through the housing (5) and connected to the laser-guide tube (19) of the drill rod (2), a transmission duct (6), the outlet aperture of which is covered in light-transmitting relationship in the region of the housing bottom (5b) by an expander lens (8), disposed in the inside space of the housing and connected to the annular space of the double tube (21) of the drill rod (2), devices for propagation and/or evaporation of the arriving liquid nitrogen as well as for the storage and splitting of gaseous nitrogen to the various provided partial streams, disposed in the housing jacket (5c) and extending in inclined manner in the direction of flow of the conveying-gas stream, conveying-jet nozzles (16, 17) for the injection of liquid and/or gaseous nitrogen into the conveying-gas stream (15), disposed in the housing bottom (5b) and directed in the direction of the borehole bottom (4b), heating-gas nozzles (9) for the heating-gas stream (10), disposed in the housing inside space, an electrical heating device (11) for the heating-gas stream (10), as well as with solenoid valves and volume-flow regulators for the control and regulation of all nitrogen partial streams.

9. The apparatus according to claim 8, wherein the partial stream serving as cooling-gas stream (24) passes through the housing inner space, wherein the housing inner space is in communication with the annular space between the outer protective tube (23) and the insulating tube (22) of the drill rod (2).

10. The apparatus according to claim 8, wherein cleaning nozzles (12), which extend parallel to the underside of the housing bottom (5b) and are aligned with an expansion lens (8) covering the transmission aperture (6) for the laser beam, are disposed in the housing bottom (5b) for the partial stream serving as cleaning-gas stream (14).

11. The apparatus according to claim 8, wherein the transmission aperture (6) for the laser beam (7) is equipped within the housing (5) of the laser-drilling head with inlet openings (20) for the partial stream serving as protective-gas stream (18).

12. The apparatus according to claim 5 wherein retaining devices (27) with spacing relative to one another for holding lens and/or mirror systems that deflect the laser beam (7) are disposed in the interior of the transmission aperture (6) for the laser beam (7) and/or of the laser-guide tube (19), wherein these retaining devices (27) are formed in a way that is permeable for the gas of the protective-gas stream (18).

Description

[0043] An exemplary embodiment of the invention will be explained in the following on the basis of the drawings, wherein

[0044] FIG. 1: schematically shows a longitudinal section through the laser-drilling head fastened to the drill rod and situated in its working position above the borehole bottom;

[0045] FIG. 2: schematically shows a cross section through the drill rod.

[0046] In the drawing, the laser-drilling head is denoted as whole with the reference numeral 1 and the drill rod carrying the laser-drilling head 1 is denoted as whole with the reference numeral 2. The laser-drilling head 1 and the drill rod 2 are situated in a borehole 4, drilled in a rock formation 3, having a borehole wall 4a and a borehole bottom 4b.

[0047] The laser-drilling head 1 held in its working position with small clearance above the borehole bottom 4b has a substantially cylindrical housing 5, the housing top 5a of which is connected with the drill rod 2.

[0048] Furthermore, the housing 5 has, disposed with spacing relative to the borehole bottom 4b, a housing bottom 5b, which is equipped in the middle with a transmission aperture 6 for a laser beam 7 supplied via the drill rod 2 and propagated through the housing 5. An expander lens 8, which broadens the arriving laser beam 7 so far that the entire borehole bottom 4b is bombarded by the laser beam 7, is situated in the transmission aperture 6.

[0049] Furthermore, heating-jet nozzles 9, which generate heating-gas streams 10 directed in the direction of the borehole bottom 4b and admit heating gas from electrical heating devices 11 disposed in the inner space of the housing 5, are situated in the housing bottom 5b.

[0050] Moreover, cleaning nozzles 12, which are aligned parallel to the underside of the housing bottom 5b in the direction of the expander lens 8 disposed in the middle, are situated in the housing bottom 5b and, by a nitrogen-collecting tank 13 situated in the interior of the housing 5, are supplied with clean gaseous nitrogen as cleaning-gas stream 14 for keeping the expander lens 8 clean.

[0051] Furthermore, the housing 5 of the laser-drilling head 1 has a housing jacket 5c, which leaves open an annular space all around relative to the borehole wall 4a for the passage of a conveying-gas stream 15 loaded with the detached rock material and ascending from the borehole bottom 4b. This conveying-gas stream 15 has its origin in the peripheral region of the borehole bottom 4b being stressed by the heating-gas stream 10 and it transports the rock material detached from the borehole bottom out of the borehole 4.

[0052] To support this ascending conveying-gas stream 15, conveying-jet nozzles 16 and 17, which extend at an inclination in the direction of the conveying-gas stream 15 and can admit liquid and/or gaseous nitrogen from the interior of the housing 5, are disposed in the housing jacket 5c of the housing 5 of the laser-drilling head 1. To the extent that liquid nitrogen is input via the conveying-jet nozzles 16, it contributes particularly intensively to cooling of rock material contained in the conveying-gas stream 15.

[0053] In order to be able to guide the laser beam 7 in the most unattenuated manner possible to the laser-drilling head 1, and in order, moreover, to be able to supply the laser-drilling head 1 with an adequate quantity of nitrogen, a specially constructed drill rod 2 is provided, which will be explained in detail in the following.

[0054] This drill rod 2 consists of several tubes disposed concentrically one inside the other, namely: [0055] an inner laser-guide tube 19, through which a protective-gas stream 18 flows, for the transmission of the laser beam 7; this protective-gas stream 18 consisting of clean nitrogen gas is supplied to the inside of the laser-guide tube 19 above the transmission aperture 6 within the housing 5 of the laser-drilling head 1, and specifically via inlet openings 20, situated in the interior of the housing 5, into the transmission aperture 6; [0056] concentrically surrounding the laser-guide tube 19 with radial clearance, a double tube 21, through the annular space 21a of which liquid nitrogen flows; [0057] an insulating tube 22, concentrically surrounding the double tube 21 with radial clearance; [0058] and an outer protective tube 23, concentrically surrounding the insulating tube 22 with radial clearance.

[0059] These annular spaces, surrounding the double tube 21, relative to the laser-guide tube 19 and relative to the insulating tube 21, are evacuated, in order to keep the liquid nitrogen flowing through the annular space of the double tube 21 adequately thermally insulated.

[0060] The annular space between the outer protective tube 23 and the insulating tube 22 is connected to a cooling-gas stream 24, which is returning from the housing 5 of the laser-drilling head 1 and which cools the outside of the drill rod 2 adequately.

[0061] This outer protective tube 23 consists of steel and ensures good stability and loadability of the entire drill rod 2 contrast, all tubes situated in the interior of the protective tube 23, namely the laser-guide tube 19, the double tube 21 and the insulating tube 22, consist of carbon-fiber-reinforced plastic (CFP).

[0062] Furthermore, one or more of the tubes surrounded by the outer protective tube 23 is or are equipped with electrical conductors, not illustrated in detail in the drawing, for transmission of electrical energy and electrical signals in the direction of the laser-drilling head 1.

[0063] For simplification of the handling of the drill rod 1, this is subdivided into longitudinal portions, which can be respectively joined with one another at their ends by threaded socket-and-spigot joints 25, 26, wherein the mutually adjoining portions of the laser-guide tube 19 as well as of the annular space of the double tube 21 and of the annular space between the outer protective tube 23 and the insulating tube 22 are joined in aligned and pressure-tight manner with one another in the region of these socket-and-spigot joints 25, 26. Moreover, the mutually adjoining portions of the electrical conductors are connected with one another in electrically conducting manner there. In contrast, the annular spaces present in the individual portions of the drill rod 2 and evacuated for the purpose of insulation of the double tube 21 are respectively closed individually in pressure-tight manner and are not joined with one another.

[0064] Finally, retaining devices 27 with spacing relative to one another for holding of the lens or mirror systems that deflect the laser beam 7 are disposed in the interior of the transmission aperture 6 for the laser beam 7 and/or of the laser-guide tube 19, wherein these retaining devices 27 are formed in a way that is permeable to the protective-gas stream 18, i.e. are equipped at the periphery with corresponding through-holes.

[0065] Several solenoid valves and volume-flow regulators, which can be activated via the signal conductors contained in the drill rod 2 and which distribute the liquid nitrogen supplied via the double tube 21 to the housing 5 as needed to the conveying-jet nozzles 16, 17 the collecting tank 13 for gaseous nitrogen, the heating devices 11 for the heating-gas stream 10 and the housing inside space, are situated in the housing 5 of the laser-drilling head 1. In the process, the control and regulation take place such that the system remains in thermodynamic equilibrium despite the energy being supplied with the laser beam.

[0066] The system illustrated in the drawing works in principle as follows:

[0067] A laser beam 7 with a power of 500 kW to 700 kW is injected by a high-power laser generator situated outside the borehole 4 into the laser-guide tube 19 and is guided to the laser-drilling head 1. At the same time, the laser-guide tube 19 admits, from underneath, the protective-gas stream 18 consisting of clean nitrogen gas, so that the laser beam is hardly attenuated on its way to the laser-drilling head 1. In the laser-drilling head 1, the laser beam 7 is then expanded so far with the expander lens 8 that it covers the entire borehole bottom 5b.

[0068] Simultaneously with the expanded laser beam 7, the borehole bottom 4b is stressed with the heating-gas stream 10, which has been brought beforehand by means of the heating device 11 to a temperature that is close to the melting temperature of the rock present at the borehole bottom 4b or even exceeds it. Under the effect of the laser beam 7 and the heating-gas stream 10, rock material at the surface of the borehole bottom 4b is stripped by melting, evaporation or spalling and forced by the heating-gas stream 10 toward the outer periphery of the borehole bottom 4b.

[0069] In the process, an upwardly directed conveying-gas stream 15 containing the stripped rock material is formed in this peripheral region and pushes upward through the annular space between the housing jacket 5c and the borehole wall 4a.

[0070] Liquid nitrogen and/or gaseous nitrogen is then blown into this ascending conveying-gas stream by means of the conveying-jet nozzles 16 and 17, whereby the conveying-gas stream 15 is cooled and at the same time intensified. This conveying-gas stream 15 loaded with the rock material is then transported out of the borehole 4 via the annular space between the drill rod 2 and the borehole wall 4a.

TABLE-US-00001 LIST OF REFERENCE SYMBOLS 1 Laser-drilling head 2 Drill rod 3 Rock formation 4, 4a, 4b Borehole, Borehole wall, Borehole bottom 5, 5a, 5b, 5c Housing, Housing top, Housing bottom, Housing jacket 6 Transmission aperture 7 Laser beam 8 Expander lens 9 Heating-gas nozzle 10 Heating-gas stream 11 Heating device 12 Cleaning nozzle 13 Collecting tank for nitrogen gas 14 Cleaning-gas stream 15 Conveying-gas stream 16 Conveying-jet nozzles 17 Conveying-jet nozzles 18 Protective-gas stream 19 Laser-guide tube 20 Inlet openings 21 Double tube 22 Insulating tube 23 Protective tube 24 Cooling-gas stream 25/26 Socket-and-spigot joint 27 Retaining devices