DRILLING DEVICE

Abstract

The invention relates to a drilling device for hard rock using a fluid, having at least one drill head with a pre-chamber and a mixing chamber where at least one front-facing nozzle and at least one rear-facing nozzle are provided. The fluid is mixed with abrasives in the mixing chamber, and the fluid together with the abrasives exits from the front-facing nozzle or an opening. The fluid flow is separated in the region of the pre-chamber, abrasive-free fluid exits the rear-facing nozzles, abrasives and the abrasive-free fluid are mixed in the mixing chamber, and the fluid mixed with the abrasives exits from the front-pacing nozzle or an opening.

Description

The invention relates to a drilling device for hard rock using a fluid, having at least one drill head with a pre-chamber and mixing chamber, at least one front-facing nozzle and at least one rear-facing nozzle.

It is generally known that abrasives can be added to a drilling fluid to increase the drilling progress rate for water jet-based drilling techniques. This can also be done with radial jet drilling (RJD) to improve the process. With the current use of pure water as cutting and drilling fluid alone, extremely hard rock layers cannot or only with difficulty be drilled through. However, by adding abrasives to the drilling fluid, harder rocks or rock layers can be penetrated. However, this method in the drill head can damage the inner geometry of the drill head and the water supply line to the drill head and slow down the advance speed.

In U.S. Pat. No. 6,932,285 B1, for example, the principle of feeding abrasives to a mixing chamber pressurized with water is disclosed, with the abrasives being fed radially via a lateral supply line. U.S. Pat. No. 6,932,285 B1 also shows a device as a water jet drilling device, in which water is mixed with abrasives in a mixing chamber and can exit from an outlet nozzle.

U.S. Pat. No. 6,263,984 A1 describes the use of a device as a water jet drilling device, in which rear-facing nozzles are arranged from which water with abrasives can exit. Water with abrasives also hits a rotating body, causing it to rotate, whereby the water with the abrasives can subsequently exit from the outlet nozzles.

CN 104033106 A shows a drill head for a water jet drilling device, which has a mixing chamber and a rotating body over rear-facing drilling nozzles and backward directed nozzles, wherein a fluid can exit from the drill head via rotating outlet nozzles.

Furthermore, an external supply of abrasives near the drill head by magnetically induced force fields is known. Due to the locally very high flow velocities of the fluid and the particles, the particles have a very high impulse, which in addition to the acting fluid forces must be overcome by the magnetic field to force it onto another “fluid path.” In addition, the magnetic fields must direct the small particles into extremely small openings in the drill head, which in practice cannot be safely guaranteed without considerable effort. In addition, the rock layer drilled through can have just as negative an influence on the magnetic field as ambient temperatures of up to 200° C. in geothermal reservoirs.

The problem with the known prior art is that when a mixture of abrasives and drilling fluid is conveyed to the drill head, increased wear can occur in the supply line and the drill head. The drill head—all or part of the drilling device—can be damaged by the exit of abrasives at the side nozzles, if any, and at the supply lines, which are not based on plastics.

The object of the invention is to provide a fluid-based drilling device for hard rocks and/or rock layers, which on the one hand guarantees to protect the drill head and the drill supply lines from greater damage and increased wear and/or enables fluid-based bores with the aid of a rotating, pulsating fluid jet.

According to the invention, this object is solved by the features of the independent claim 1.

The development of geothermal reservoirs and oil/gas reservoirs in extremely hard rock layers often cannot take place without the use of hydraulic or chemical stimulation. Alternatively, the RJD drilling method can be used to drill thin, long underground bores from a main borehole.

In order to make bores in hard rock possible with this method, abrasives can be conducted via an abrasive-containing supply line into a mixing chamber in the drilling head, wherein mixing of abrasives and an abrasive substance-free fluid takes place in the mixing chamber and the fluid mixed with the abrasives exit from a front-facing nozzle and makes a drilling process possible, wherein at least one rear-facing jet is arranged in the region of the drill head, from which fluid exits without abrasives in order to ensure a continuous, sliding drilling process.

The drilling device and the drilling method can be seen as an environmentally friendly alternative to “fracking.” With RJD drilling, it is possible to drill long thin bores in the hard rock instead of hydraulic crack generation, which also makes it possible to develop deposits. The drilling device and the method are also suitable as a separate drilling method for coiled tubing applications (CT drilling) as well as for drilling small individual bores in the formation from an existing bore, also by using CT drilling.

By adding abrasives to the fluid in the mixing chamber to the at least one front-facing nozzle, extremely hard rocks and/or rock layers can be drilled through or cut and deposits behind them can be tapped. The abrasives used, according to the invention, are dispersed solids such as metal salts such as iron oxides, silicates such as silicon oxide or other ionic, amorphous or metallic solids, which can be supplied externally to the drilling device via a supply line. The abrasives are fed into the drill head according to the invention via an abrasive-containing supply line into a mixing chamber. In this mixing chamber the abrasives are mixed with an abrasive-free fluid. The fluid without abrasives enters the pre-chamber via an abrasive-free supply line into the drill head and is fed into the mixing chamber via supply lines and/or focusing nozzles and only mixed with abrasives in a mixing chamber.

In a special embodiment of the object of the invention, it is also provided that the abrasives are only produced in the drilling device, for example by guiding metal strips or other strand-like solids into the drilling head via the abrasive-containing supply line, where they are crushed into abrasives or by producing the disperse abrasives in situ, for example by rotating removal of the metal strips or the strand-like solids in the area of the drilling head.

The pre-chamber and mixing chamber are spatially separated from each other according to the invention. In the area of the drill head, one or more rear-facing nozzles are arranged, by means of which the fluid is introduced into the borehole without abrasives and/or can be used as a driving agent and/or lubricant for the drill. The number of rear-facing nozzles depends on the respective design of the drill head and the purpose of the drilling device. In addition, there can also be flushing outlets in the area of the drill head in order to flush out removed rock from the borehole and ensure uniform driving of the drilling device.

In one advantageous embodiment the spatial separation of the pre-chamber and mixing chamber can also provide that the mixing chamber is located at the tip of the drill head and open in the direction of the rock or sediment or material to be removed, i.e. the drill head is equipped with the open mixing chamber. Accordingly, the pre-chamber and mixing chamber do not necessarily have to be designed as closed units within the drill head and the tip of the drill head can have an opening as an open mixing chamber directly, i.e. with direct contact to the drilling environment, whereby the front-facing nozzles loaded with abrasive-free fluid mix the abrasive-containing fluid in the open mixing chamber and move it in the direction of the opening. The abrasive-free fluid can be directed into the drill head via one or more focusing nozzles and can reach the open mixing chamber from at least one front-facing nozzle. The front-facing nozzle can also be designed as a focusing nozzle. The abrasive-containing fluid is fed via an internal or external supply line to the abrasive-free fluid in the open mixing chamber, whereby the abrasive-containing fluid mixed with the abrasive-free fluid is subsequently removed from the open mixing chamber in the direction of the rock, sediment or material from the opening of the open mixing chamber.

The outer lateral boundaries of the tip of the drill head are tapered towards the opening of the open mixing chamber, wherein tapered means that the lateral boundaries of the open mixing chamber have an angle within a range of 10° to 45° of the longitudinal center axis of the drilling device. The conical shape of the side surfaces of the open mixing chamber allows the abrasive fluid to be focused on the rock, sediment or material to be removed and thus ensures better driving of the drilling device during the drilling process. In addition, it is possible, analogous to the above designs, to feed abrasive fluid from the borehole via an external supply line into the open mixing chamber, wherein such external supply line can be cumulative or alternative to an already existing external supply line for abrasive fluid on the drilling device.

In the mixing chamber or open mixing chamber, the fluid, for example a liquid, in particular water, is mixed with abrasives in order to serve as an additive, with the aid of which a material removal of the subsoil and a drilling can take place via the front-facing nozzles at the drill head. The fluid used usually has a viscosity of η=1 to 20 Pa s at 20° C., but can also contain mixtures or dispersions of water with other compounds such as for example ethylene glycol. The choice of fluid depends on the intended use, in each case, and the type of rock to be drilled.

According to the invention, it is therefore intended to divide a fluid flow for the rear-facing nozzles and flushing outlets without abrasives and a fluid flow with abrasives for the front-facing nozzles. The fluid for the rear-facing nozzles and the flushing outlets will generally have the same composition as for the front-facing nozzles with the limitation that the fluid for the front-facing nozzles in the mixing chamber will be additionally mixed with abrasives. However, it is alternatively provided that the abrasives may be fed to the mixing chamber with a fluid in which the abrasives are at least dispersively distributed. The abrasive-free fluid may then be mixed with the abrasive-containing fluid in the mixing chamber or in the open mixing chamber, whereby the composition of the fluids with and without abrasives may differ.

The supply of the abrasive materials can be made possible by external or internal supply lines into the drill head. For this purpose, a special embodiment of the object of the invention allows the supply lines to run coaxially to the drill head, which has the advantage that the fluid entry of the flushing fluid and/or the abrasives is uniform and the driving is not hindered by the coaxial arrangement of the supply lines. It is also provided in a special embodiment that the supply lines both run inside and/or coaxially in the drilling device to the drill head. The drilling device according to the invention can have several rear-facing and several front-facing nozzles, as well as several flushing outlets.

The advantage of the inventive drilling device is that damage to the drill head is avoided by the use of the abrasive-free fluid in the rear-facing nozzles and/or flushing outlets. The drilling method is thus an alternative to conventional drilling methods and, in contrast to hydraulic stimulation, it is possible to predict the length of the borehole and the extent of the contact surface between the borehole and the reservoir. In addition, the drilling of a borehole only takes a few minutes. Moreover, by refraining from breaking up the subsoil, no seismicity is induced in the rock. The fact that water or other non-toxic compounds in particular can be used as fluids means that, unlike the use of other fluids in other drilling devices and methods, the subsoil is not contaminated according to the prior art.

According to the invention, an effective material removal can be guaranteed by the fact that rear-facing nozzles and/or flushing outlets are also arranged in the area of the pre-chamber at the drill head in order to be able to drill further or deeper with the same power. This represents a particular advantage of the inventive drilling device and the method, since according to the current state of research, the pumping capacity represents a limiting factor in the length of the bore. An abrasive-free fluid flow emerges from the rear-facing nozzles and/or flushing outlets, which minimizes the friction forces acting on the drill head and the supply lines. The drill head can be pushed further in the direction of the rocks and/or rock layers than in the absence of them by means of the fluid of the rear-facing nozzles, based on the assumption that the rock properties are approximately constant in the horizontal direction.

In one particular embodiment, the drill head has a rotating inner part, which is mounted on an axis on the housing of the drill head. The fluid mixed with the abrasives can emerge from the area of the rotating inner part via at least one forward rotating nozzle and/or opening. Essentially, this means that the front-facing nozzles have an orientation or tilt of less than 90° with respect to the drill head, the relative tilt angle varying with the nature of the subsoil.

The advantage of the rotating inner part is that there is uniform material removal on the borehole wall. With conventional drilling heads of the RJD drilling method, the orientation of the front-facing nozzles is static. This means that material is removed only selectively. The entire surface of the borehole wall is uniformly machined by the rotation.

In the case of the special embodiment with rotating inner part, the drill head comprises at least one focusing nozzle on the rotating inner part and at least one hole on the static area (stator) of the drill head for regulating the water supply. In the case of the special embodiment with rotating inner part, the drilling device according to the invention comprises at least one mixing chamber or open mixing chamber, at least one pre-chamber, at least one rear-facing nozzle and/or flushing outlet, at least one transition line for the abrasives and at least one front-facing nozzle and/or opening. In a particularly advantageous embodiment, the rotating inner part has three holes and the stator four holes for regulating the water supply, so that at least one or none of the holes can overlap with the focusing nozzle during rotation of the inner part. Due to the periodic overlapping of the holes of the stator with the focusing nozzle of the rotating inner part, a pulsation of the fluid flow can occur, whereby the frequency of the pulsation is made possible by different rotational speeds of the inner part. When the drill holes overlap with the focusing nozzle, the abrasive is forced into the front-facing nozzle, so that when the drill holes and the focusing nozzle overlap, the fluid pushes the abrasive out of the front-facing nozzle in an intermittent manner and generates a pulsed fluid flow. Such a generation of a pulsating fluid flow must take place in the drill head or directly in front of it. In contrast, generation in the pump results in the pulsating movement being damped by the dynamic properties of a long hydraulic line (fluid inertia and line compressibility) and, if necessary, completely compensated up to the drill head.

During the rotation of the inner part, the rear-facing nozzles and/or flushing outlets are acted upon with abrasive-free fluid in the absence of an overlap between the bores of the stator and the rotating inner part, whereby the fluid serves on the one hand as a lubricant within the hole and on the other hand as a driving medium for the drilling process. According to the invention, the rear-facing nozzles run diagonally to the longitudinal center axis of the drill head, so that a propulsion of the drill head and a removal of excavated rock or subsoil out of the drill hole is facilitated by the diagonal arrangement of the rear-facing nozzles and/or the flushing outlets. In addition, the fluid, such as water or mixtures of water with hydrocarbons, acts as a lubricant between the rotating inner part, the pre-chamber and the drill head housing.

The rotation of the inner part can be achieved by the rotating inner part enclosing an acute angle in the range of 1° to 11° with respect to the housing of the drill head. By switching the focusing nozzles on the rotor and the holes on the stator, fluid is applied to the drill head, inducing rotation of the inner part. In the area of the rotating inner part there is an annular gap between the housing of the drill head and the rotating inner part, which can vary in size and width depending on the intended use of the drilling device. There may also be a lubricating gap between the rotating inner part and the static portion of the drill head, into which abrasive-free fluid can enter and which facilitates sliding of the rotating inner part along the surface of the static portion of the drill head.

In a special embodiment, the object of the invention has an external supply line at the drill head for fluid containing abrasives, whereby the fluid containing abrasives can be removed from the borehole. The external supply line for abrasive materials from the borehole can be present in the object of the invention in parallel or at the same time as an internal supply line for fluids containing abrasive materials. The abrasive material coming from the borehole reaches the mixing chamber or open mixing chamber via a supply line containing abrasive fluids and is transported from there to the outside via the front-facing nozzles. In order to ensure a continuous and/or constant supply of abrasives from the borehole into the drill head, guide plates are advantageously arranged on the outside of the drill head, which direct the abrasives in the direction of the supply line for abrasive materials and/or the mixing chamber or open mixing chamber.

The inventive SMC drilling device is used in particular for the development of geothermal reservoirs, oil/gas reservoirs, anchor boreholes, exploration boreholes, stimulation boreholes and/or for CT drilling.

The invention is described again in detail using the following figures:

FIG. 1 shows a simplified principle of the inventive drilling device 1 for hard rock in a vertical cross section of the drill head 2. Inside the drill head 2 runs a supply line 6a for the supply of abrasive-free fluid into the pre-chamber 8 and a supply line 6b for the supply of abrasives 5 (not shown) into a mixing chamber 3. Pre-chamber 8 and mixing chamber 3 are separated and arranged one behind the other in the direction towards the front-facing nozzle 4, so that the abrasive-free fluid enters the mixing chamber 3 via the pre-chamber 8 and a focusing nozzle 14 and can be mixed there with the abrasives 5 (not shown). The abrasive-free fluid is discharged from the drill head 2 into a borehole via a rear-facing nozzle 7. The rear-facing nozzle 7 is arranged at an angle to the central longitudinal axis of the drill head 2 and allows the use of the abrasive-free fluid as a propulsion agent and/or lubricant for the drilling device 1. On the other hand, the abrasive-containing fluid with the abrasive-free fluid serves as a cutting jet, which can continuously exit from the front-facing nozzle 4 of the drill head 2, whereby the abrasive-free fluid from the pre-chamber 8 enters the mixing chamber 3 via a focusing nozzle 14.

FIG. 2 shows a drilling device 1 according to the invention with a rotating inner part 9 in a vertical cross section. The drilling head 2 contains the housing of the drilling head 2, which comprises a static area of the housing as stator 11 and a rotating inner part 9. One recognizes the abrasive-free supply line 6a through which a fluid can enter the pre-chamber 8 of the drilling head 2. A rear-facing nozzle 7 is arranged obliquely to the longitudinal center axis from the pre-chamber 8, by means of which abrasive-free fluid can exit into the borehole. Via a transition line 12, abrasive-containing fluid passes from an abrasive-containing supply line 6b into the mixing chamber 3, in which the abrasive-free fluid is mixed with abrasive 5 (not shown). The rotating inner part 9 has a focusing nozzle 14 pointing towards the pre-chamber 8 or holes 13 of the static area of the drill head 2. This design arrangement of the holes 13, transition line 12 and focusing nozzle 14 is shown in the sectional views A-A and B-B.

The inner part 9 is spaced from the housing of the drill head 2 by an annular gap 10. As the inner part 9 rotates, part of the holes 13 of the pre-chamber 8 overlap with part of the focusing nozzle 14 of the rotating inner part. If the holes 13 of the pre-chamber 8 are congruent with the focusing nozzle 14, abrasive-free fluid enters the mixing chamber 3. The fluid mixed with the abrasives can then exit from the drill head 2 via the front-facing nozzle 4 and act as a cutting jet. The rotation of the inner part 9 is produced by the continuous application of abrasive-free fluid to at least one existing focusing nozzle 14, which is not congruent with the hole 13 of the static part of the drill head 2 with the abrasive-free fluid, the position of the focusing nozzle 14 forming an acute angle with respect to the drill head 2 of the inner part 9.

FIG. 3 shows a design embodiment of the drilling device 1 with an analogous structure to FIG. 2. Abrasive-free fluid is fed via an abrasive-free supply line 6a to the pre-chamber 8, which is partly located in the rotating inner part 9. The rear-facing nozzles 7 are arranged in the rotating inner part 9 at the pre-chamber 8. The rotating inner part 9 consists of two parts pressed into one another, wherein via an abrasive-containing supply line 6b a supply of abrasives 5 (not shown) into the mixing chamber 3 is made possible, which is arranged in the rotating inner part 9. A special feature of this embodiment is the branch of the abrasive-free fluid at the supply line 6a. The lubricating gap 15, at which a rotary movement of the rotating inner part 9 relative to the housing of the drill head 2 occurs, is acted upon with abrasive-free fluid. Since the pressure of the non-abrasive fluid is considerably higher than that of the fluid containing the abrasive, the non-abrasive fluid flows through the lubricating gap 15 and prevents the penetration of the abrasive 5 (not shown) into lubricating gap 15.

While the high pressures of the abrasive-free fluid generate a force in the rotating inner part 9, depending on the design, but especially in this design, which axially push out the rotating part 9, a pressure is built up in the annular gap 10 which generates an axial force which counteracts this. The annular gap 10 is designed so that the projected area of the annular gap 10 is larger than the hydraulically effective area, which would cause the rotating inner part 9 to be pushed out of the drill head 2. The supply of abrasive-free fluid to this annular surface of the annular gap 10 takes place through a line 17, in which a pressure drop is generated depending on the flow. If the rotating inner part were to be in contact with the cone, no fluid would be able to flow and no pressure would drop in line 17. The force is now greater due to the larger area of the annular gap 10 and presses the rotating inner part 9 into the drill head. Thus, fluid can flow by opening the annular gap 10, the pressure drop of the line 17 rises with flowing fluid, until a force and pressure equilibrium is achieved, which centers the rotating inner part 9 axially and forms an axial slide bearing. The fluid enabling this centering can exit from the flushing outlets 16 of the drilling device 1.

FIG. 4 shows a variation of FIG. 2 with the abrasive supply line 6b in the middle of the drilling device 1 through the pre-chamber 8. The drill holes 13 for generating pulsation are arranged around this supply line 6b by an overlap as described in FIG. 2. The rear-facing nozzles 7 are arranged in the static part of the drill head 2. The central supply allows the supply of a strand-like abrasive, which is crushed by the rotation of the rotating inner part 9 in the mixing chamber 3.

FIG. 5 shows a further particular configuration of the object of the invention in a vertical cross section. In this special embodiment of the drilling device 1, the mixing chamber 3 is designed as an open mixing chamber 19, i.e. it is located at the tip of the drilling head 2 and is often open or has an opening 20 in the direction of the rock, sediment or material to be impacted by the abrasive fluid. It can be seen that the drilling device 1 has a rotating inner part 9. The rotating inner part 9 has a focusing nozzle 14 pointing towards the rotating inner part 9 and/or the open mixing chamber 19. The drill head 2 contains the housing of the drill head 2 with a static area of the housing as stator 11 and a rotating inner part 9. An abrasive-free fluid is introduced into the pre-chamber 8 of the drill head 2 via the abrasive-free supply line 6a. From the pre-chamber 8, a rear-facing nozzle 7 is arranged obliquely to the longitudinal center axis, by means of which abrasive-free fluid can exit into the borehole. The abrasive-free fluid is fed into the open mixing chamber 19 via the front-facing nozzle, which is designed as focusing nozzle 14 here. The abrasive fluid in the open mixing chamber 19 is mixed with the non-abrasive fluid via an external supply line 6b, whereby the abrasive fluid mixed with the non-abrasive fluid can subsequently exit from the open mixing chamber 19 in the direction of the rock, sediment or material to be removed from the opening 20. The outer lateral boundaries of the tip of the drill head 2 are conical in the direction of opening 20 of the open mixing chamber 19, thus allowing the abrasive fluid to focus on the rock, sediment or material to be removed. In addition, it is possible (not shown) to lead abrasive fluid from the borehole via the external supply line 6b and/or another supply line into the open mixing chamber 19, analogous to the comments on FIG. 6.

FIG. 6 shows an additional possible embodiment of the object of the invention in a vertical sectional drawing. In this case, an abrasive-containing fluid passes from a supply line 6b arranged externally to the drill head 2 and containing abrasive into the open mixing chamber 19, whereby the abrasive-containing fluid is mixed with abrasives 5 from the borehole (not shown). It is also provided in order to ensure a continuous and/or constant supply of the abrasives 5 from the borehole via the supply line 6b into the open mixing chamber 19, a guide plate 18 is arranged on the outside of the drill head 2, which guides the abrasive materials 5 in the direction of the supply line 6b and ensures that the abrasives 5 from the borehole are mixed continuously and/or constantly with the abrasive-free fluid before they leave the opening 20.

REFERENCE SIGN LIST

• 1 Drilling device
• 2 Drill head
• 3 Mixing chamber
• 4 Front-facing nozzle
• 5 Abrasives
• 6a Abrasive-free supply line
• 6b Abrasive supply line
• 7 Rear-facing nozzle
• 8 Pre-chamber
• 9 Rotating inner part
• 10 Annular gap
• 11 Stator
• 12 Transition line
• 13 Bore
• 14 Focusing nozzle
• 15 Lubrication gap
• 16 Flushing outlet
• 17 Line
• 18 Guide plate
• 19 Open mixing chamber
• 20 Opening

Claims

1-15. (canceled)

16. A drilling device for hard rock with a drilling fluid, the drilling device comprising

a drill head for being positioned facing said hard rock,

a pre chamber and a mixing chamber being arranged within said drilling head;

at least one distal opening located in said drilling head

at least one rear-facing nozzle provided in said drilling head

wherein said pre chamber is connected to said mixing chamber by a first supply line;

wherein a second supply line is connected to said pre chamber for delivering an abrasive-free fluid

wherein a third supply line is connected to said mixing chamber for delivering an abrasive stream;

wherein said mixing chamber mixes said abrasive stream and said abrasive-free fluid to obtain said drilling fluid;

wherein said at least one distal opening is arranged downstream the mixing chamber; and

wherein said at least one rear-facing nozzle is arranged such that the drilling fluid delivered by said at least one distal opening is repelled by said hard rock being discharged by abrasive-free fluid from said at least one rear-facing nozzle.

17. The drilling device according to claim 16,

wherein the pre chamber and the mixing chamber are arranged spatially separated from each other in the drill head.

18. The drilling device according to claim 16,

wherein said abrasive-free supply line and said abrasive supply line run inside the drilling device.

19. The drilling device according to claim 16,

wherein said at least one abrasive-free supply line runs coaxially to an axis of the drill head.

20. The drilling device according to claim 16,

wherein the abrasives reaching the mixing chamber via the abrasive supply line are received from a borehole using a guide plate arranged on the outside of said drill head.

21. The drilling device according to claim 16,

wherein the mixing chamber is embodied together with said at least one opening to define an open mixing chamber facing said hard rock.

22. The drilling device according to claim 16,

wherein the drill head runs at least partially conical in a direction of said opening.

23. The drilling device according to claim 16, wherein

the abrasives reaching the mixing chamber via the abrasive supply line are received from a borehole using a guide plate arranged on the outside of said drill head,

the mixing chamber is embodied together with said at least one opening to define an open mixing chamber facing said hard rock, and

the abrasives from the borehole reach the open mixing chamber via said abrasive supply line, wherein said abrasive supply line is radially oriented in said drill head.

24. The drilling device according to claim 16,

wherein the rear-facing nozzles are arranged obliquely to a longitudinal center axis of the drill head.

25. The drilling device according to claim 16,

wherein the drill head comprises a rotating inner part.

26. The drilling device according to claim 25,

wherein the rotating inner part comprises at least one focusing nozzle, and wherein the rotating inner part comprises at least one transition line providing a connection from said abrasive supply line to said mixing chamber.

27. The drilling device according to claim 25,

wherein an annular gap is radially provided between a receiving part of the drill head and the rotating inner part.

28. The drilling device according to claim 27,

wherein the annular gap has a projected area being larger than a hydraulically effective area of the said annular gap, and

wherein said rotating inner part of said drill head and said abrasive-free fluid provide a hydrodynamical bearing within said annular gap.

29. The drilling device according to claim 25,

wherein at least one of a metal strips and a strand-like solid is guided into the drill head via said abrasive supply line, and

wherein the abrasives are produced by the rotating inner part thus cutting said at least one of said metal strips and said stand-like solid into abrasive debris.

30. Use of the drilling device according to claim 16 for employing a site selected from a group comprising geothermal reservoirs, oil reservoirs, gas reservoirs, anchor boreholes, exploration boreholes, stimulation boreholes, boreholes for CT drilling and combinations thereof.

31. A drilling device for hard rock with a drilling fluid, the drilling device comprising

a drill head for being positioned facing said hard rock, the drill head having a longitudinal axis,

a pre chamber and a mixing chamber being arranged within said drill head;

at least one distal opening located in said drill head; and

at least one rear-facing flushing outlet provided in said drill head;

wherein said pre chamber is connected to said mixing chamber by a first supply line;

wherein a second supply line is connected to said pre chamber for delivering an abrasive-free fluid;

wherein a third supply line is connected to said mixing chamber for delivering an abrasive stream;

wherein said mixing chamber mixes said abrasive stream and said abrasive-free fluid to obtain said drilling fluid;

wherein said at least one distal opening is arranged downstream the mixing chamber; and

wherein said at least one rear-facing flushing outlet traverses the drill head in a direction transverse to said longitudinal axis,

wherein the at least one rear-facing flushing outlet is connected to one of said second supply line and said pre chamber,

such that the drilling fluid delivered by said at least one distal opening and repelled by said hard rock is lead away by abrasive-free fluid discharged from said at least one rear-facing flushing outlet.

32. A drilling device for hard rock with a drilling fluid, the drilling device comprising

a drill head for being positioned facing said hard rock,

a pre chamber and a mixing chamber being arranged within said drill head;

at least one distal opening located in said drill head; and

at least one rear-facing flushing outlet provided in said drill head;

wherein said pre chamber is connected to said mixing chamber by a first supply line;

wherein a second supply line is connected to said pre chamber for delivering an abrasive-free fluid;

wherein a third supply line is connected to said mixing chamber for delivering an abrasive stream;

wherein said mixing chamber mixes said abrasive stream and said abrasive-free fluid to obtain said drilling fluid;

wherein said at least one distal opening is arranged downstream the mixing chamber; and

wherein said at least one rear-facing flushing outlet is arranged radially to the said pre chamber,

such that the drilling fluid delivered by said at least one distal opening and repelled by said hard rock is lead away by abrasive-free fluid discharged from said at least one rear-facing flushing outlet.

33. The drilling device according to claim 32,

wherein said at least one distal opening is selected from the group comprising an opening, a plurality of openings, a nozzle, a plurality of nozzles, a channel and a plurality of channels.

34. The drilling device according to claim 32,

wherein said at least one distal opening is oriented with an acute angle with respect to an axis of said drilling head.

35. The drilling device according to claim 32,

wherein said drill head includes a rotatable inner part,

wherein said rotatable inner part is radially supported within said drill head,

wherein the rotatable inner part is arranged downstream said pre chamber, and

wherein the rotatable inner part includes a fluid supply line rotating around a rotational axis of said rotatable part.