EP0134467A2 - Target-directed drilling rod for rotating boring tools with flushing duct for underground mining - Google Patents

Abstract

A dirigible drilling head is provided with a hydraulic pulser in its rotating inner tube in the form of a spindle piston which can obstruct the flushing medium passage and is displaced by a hydraulic circuit including a hydraulic valve. The hydraulic valve is in turn actuated by a miniature electronic circuit so that a variety of input parameters from respective sensors can be delivered to the circuit and transformed into respective hydraulic pulses which are monitored by a differential pressure pickup connected to the line feeding the flushing liquid to the string.

Description

The invention relates to a target boring bar for rotating drill pipe with rinsing channel, preferably for underground operation according to the preamble of claim 1.

Generally speaking, a target boring bar is a drill pipe installed in the drill string train, which receives and transmits measured values that originate from measuring devices and monitors in the target boring bar. The measured values indicate the course of the bore, i.e. Information about any deviations from a predefined direction of the borehole, while the guards provide measured values which enable the functional monitoring of the various devices of such a target boring bar. In particular, the invention relates to target boring bars which are provided with a device for correcting the bore. Such a device usually consists of a plurality of control bars pivotably mounted on the outer tube, which are supported on the joints of the borehole and can be individually adjusted via hydraulically actuatable cylinders in order to correct the direction of the drill pipe.

The invention is based on a known target boring bar of the latter type (DE-OS 30 00 239.2).

In the outer tube of this Zielbohrstange the hydraulically loadable displacement cylinder of the control bars are usually several, preferably for controlling _- provided, two inclinometers orthogonal to each other in vertical measuring planes oriented. Their measured values not only supply the input variables of the built-in automatic control strip adjustment, but are also transmitted to a control station arranged at the mouth of the borehole with the telemetric device This telemetric device works with electrical signals which are transmitted via conductors housed either in a trailing cable or in the drill pipes themselves. The signals transmitted in this way are sufficiently accurate because a current source which is independent of the flushing current and which supplies the signal energy and can drive the pressure generator is used for their generation and transmission, provided that the pressure generator does not receive its kinetic energy directly from the rotating inner tube. Although a battery can also be used as the current source, it is preferably a generator whose rotor is driven by the rotating inner tube.

However, the conductor connection required for the transmission of the signals has a disadvantageous effect.

When placed in the drill string, it is difficult to make and maintain proper contact between the drill pipes. If the telemetric device uses a trailing cable, the connection is electrically perfect, but is subject to all mechanical and other stresses caused by the rotating drill pipe, the borehole joints and the borehole irrigation.

However, a target drill rod designed as a drill collar is known (DE-OS 29.41 102), which is designed as a rotating drill pipe. The purge stream running through the purge channel and a hydraulic converter, which converts the electrical signals into pressure pulses of the purge, serve as the telemetric device. The pressure-modulated flushing stream can be measured at the borehole exit, whereby the pressure impulses can be picked up by a receiver and converted into electrical quantities for transmission. A tube valve in the drill collar serves as a converter for the pressure modulation of the flushing flow, which throttles the flushing flow and is actuated with the help of a built-in, self-contained hydraulic circuit. The hydraulic working medium is controlled by means of a solenoid valve which is charged with the electrical inclination data.

Such a telemetric device requires an axial arrangement of the pipe valve, i.e. ahead of the valve body concentrically in a flushing channel, which bypasses the flushing behind the throttle point on the tubular valve body. On the one hand, this results in a spatial problem, namely when the drill pipe having the irrigation channel is relatively thin-walled.

This is particularly the case when it is a question of the inner tube of a target boring bar of the type initially known as having an upright outer tube. On the other hand, however, a standing outer tube cannot be realized with correspondingly thick-walled drilling tubes. This requires the generator to be accommodated in the rotating drill pipe and then requires a turbine driven by the flushing to drive the generator.

Because of the pressure-modulated purge flow and other variables influencing the purge flow, this turbine causes errors in the formation of the electrical signals that are to be transmitted. As a result, they are Pressure signals characterized by a non-uniform, but in any case flat pressure rise and fall when they are generated and transmitted with the known device. This is disadvantageous because not only does it make it more difficult to recognize the pressure signals, but the signal frequency also remains low and the accuracy of the data to be transmitted in this way remains limited.

The invention has for its object to improve the telemetric device in a simple manner with a target boring bar of the type presupposed as known with the aim of eliminating the electrical line connections in the borehole to the outside, but the signals generated with the built-in electro-hydraulic device with the required Transmit accuracy.

According to the invention this object is achieved with the features of claim 1. Appropriate embodiments of the invention result from the subclaims.

The elimination of the electrical line connections is achieved according to the invention through the use of the flushing stream running through the flushing channel as a telemetric device and the transducer required for pressure modulation. However, this principle is at the basic structure of the invention according Zielbohrstange _E nZielbohrstange only through the miniaturization of the converter allows the can therefore be accommodated in the limited space, while at the same time ensuring the required form of the pressure pulses. This miniaturization of the transducer is done by moving all parts and assemblies downstream of the spindle piston and its piston recess into the outer tube, while the arrangement and design of the spindle piston can generate pressure pulses that are essentially rectangular, ie have a steep pressure increase and decrease. They enable the recording of the pressure pulse between these two branches of the pressure signal and thereby a high signal frequency with which a correspondingly large amount of precise and different data can be transmitted.

The invention therefore has the particular advantage that, in addition to the signals supplied by the inclinometers, a large number of further data of the target boring bar can also be transmitted to the outside. The necessary measuring devices and monitors can be accommodated in the standing and therefore relatively less mechanically stressed outer tube and only the signals they deliver after conversion into hydraulic pulses for the spindle piston can be transferred to the flushing flow. You can use it not only to monitor the correct control of the target boring bar according to the predefined borehole course, but also to ensure the proper functioning of the hydraulic and electrical equipment required for this purpose with suitable devices and monitors.

Preferably and according to a further feature of the invention, the spindle piston is supported on one or both sides and it is acted upon with the hydraulic working medium according to electrical signals according to the feature of claim 2. In the case of small borehole diameters with a correspondingly weak inner tube of the target boring bar with a sufficiently dimensioned flushing channel, preference is given to the double-sided one Bearing of the spindle piston, which is then supported in its recess on both sides of the flushing channel.

In particular for the latter embodiment of the invention, the further development according to claim 3 is recommended. It enables a structurally simple construction of the inner tube and a correspondingly simplified production, in which the spindle piston recess can only be drilled and the connections to the directional control valve can be created essentially with grooves. which are relatively easy to seal with ring seals and can be attached by broaching or milling.

A generation of pressure pulses independent of the flushing flow is ensured in that, according to an embodiment of the invention, the pulse piston is mounted twice in the rotating inner tube and is arranged transversely to the drilling direction. It is supplied by the hydraulic pump, which is arranged in the non-rotating outer tube, between two shaft seals and thus moves the flushing channel back and forth more or less constrictively in the rotating inner tube.

A flawless and secure supply of the pulse piston is achieved since, according to the invention, a rotary leadthrough is provided in the area of the pulse piston between the rotating inner tube and the non-rotating outer tube.

The energy supply, which is independent of the flushing current, can be achieved in particular by associating the non-rotating outer tube with a boring bar generator that is designed as a slow-moving motor and can be driven by the inner tube.

To secure the hydraulic pump, a pressure limiting valve is assigned to it according to a further embodiment of the invention. Excess pressure medium is discharged into the hydraulic tank via the pressure relief valve.

A control of the pulse piston that corresponds exactly to the measured values obtained is achieved by controlling a solenoid valve that can be switched via the electronic control in the hydraulic line between the hydraulic pump and the pulse piston. Via this solenoid valve, the respective pulse can be designed exactly according to the measured value determined.

It is useful to use the inclinometer as well as the direction indicator, temperature, pressure and voltage meter as a measuring sensor, which are arranged in groups or individually at different locations on the outer and / or inner tube. With such sensors all important and at the same time to assess the state of the target interesting data are determined and forwarded to the drill rig.

In order to enable accurate retransmission or decoding, the evaluation unit arranged on the drilling rig is a differential pressure sensor which is coupled to a display device. The pressure pulses can thus be read immediately on the display device and, if necessary, stored and evaluated.

All of the supply energies required for the various units in the target boring bar are available if, as is provided according to the invention, the boring bar generator is equipped with a rectifier and voltage regulator and voltage converter, and the electronic control is supplied with energy by an associated transmitter.

In order to be sure that the pulses emitted by the transmitter are also correctly received and processed by the receiver, it is advantageous that the receiver of the differential pressure sensor and the transmitter of the electronic control are synchronized and switched in such a way that the synchronization is checked before each series of measurements he follows. Each pulse sequence is therefore preceded by one or two synchronizing pulses, which only allow recording if the synchronization is flawless.

Even horizontal and inclined target bores can be easily equipped with such a device, this being the case in particular when an electronically supported accelerometer serves as an inclinometer and a magnetically balanced magnetometer serves as a direction indicator. Such devices are insensitive to turning during drilling and ensure accurate determination and transmission of the required measured values.

In the case of seam-guided target bores, it is expedient to assign one or more gamma-ray sensors to the outer tube, which can be used to perfectly scan the hanging and the lying.

The technical progress of the present invention is essential because both a significantly more precise transmission of measured values to the drill rig is possible and, at the same time, precise monitoring of the drill pipe or the drill rod and the drill bit located far down the hole is achieved. Due to the precise continuous monitoring, additional and subsequent control measurements are unnecessary, which leads to a significant simplification of the entire drilling process. Due to the precise continuous transmission and recording of measured values, the course of the borehole can be continuously checked and regulated, which leads to considerable advantages in terms of drilling technology.

• Fig. 1 eine Zielbohrstange mit Bohrkrone, teilweise im Längsschnitt,
• Fig. 2 einen Querschnitt einer Zielbohrstange,
• Fig. 3 einen Längsschnitt einer Zielbohrstange,
• Fig. 4 eine vereinfachte Gesamtdarstellung einer Vorrichtung mit den dem Bohrstand zugeordneten Teilen,
• Fig. 5 ein Druckimpulsdiagramm in vereinfachter Darstellung,
• Fig. 6 die für den Impulskolben notwendige Steuerung,
• Fig. 7 eine andere Ausführung der Steuerung,
• Fig. 8 einen einseitig gelagerten Impulskolben und
• Fig. 9 in der Fig. 2 entsprechender Darstellung eine abgeänderte Ausführungsform des Spindelkolbens.

The invention is explained in more detail below with reference to exemplary embodiments shown in the drawing. Show it

• 1 is a target boring bar with drill bit, partially in longitudinal section,
• 2 shows a cross section of a target boring bar,
• 3 shows a longitudinal section of a target boring bar,
• 4 shows a simplified overall representation of a device with the parts assigned to the drilling rig,
• 5 is a pressure pulse diagram in a simplified representation,
• 6 shows the control necessary for the pulse piston,
• 7 shows another embodiment of the control,
• Fig. 8 is a one-sided pulse piston and
• Fig. 9 in the representation corresponding to FIG. 2 shows a modified embodiment of the spindle piston.

On the borehole side, the rotating drill pipe shown with only two drill pipes 40 and 41 in FIG. 4, which consists of several drill pipes screwed together, through which the forward flow of the drilling sludge is contained, ends at a target drill rod, which is arranged directly behind the drilling tool 1, which is driven with the drill pipe. The target boring bar transmits the rotary movement to the drilling tool 1 via its inner tube 4. The inner tube 4 surrounds a rinsing channel 3, which forwards the current of the drilling sludge. The inner tube is arranged concentrically in an outer tube 5 and can be rotated therein stored at 9. The outer tube has externally pivotably mounted control strips 7, which are supported on the borehole joints, so that the outer tube is held in place when the drill pipe rotates. This results in a relative rotation of the inner tube 4 in the outer tube 5.

The outer tube is used to hold the working cylinder, not shown in detail, for the control strips 7, the hydraulic device used to actuate them, and a large number of measuring devices and monitors, which are shown at 17 and 18 in the figures. The measuring devices include Inclinometers, which monitor the direction of the borehole, generally designated 27, and supply the controlled variables of an electronic control device which automatically adjusts the control strips and thereby ensures compliance with the planned drilling direction. A pump 10 installed in the outer tube generates the hydraulic operating pressure. It can be driven either directly by the rotating inner tube 4 or electrically by a generator 8. The rotor of the generator 8 has a pinion 15 which meshes with a toothing of the inner tube 4, so that the generator is in turn driven by the inner tube 4. In this way, the operation of the hydraulic device and the energy for the measured values and their transmission to the hydraulic device are independent of the living energy of the flushing stream.

The generator 8 is therefore also used to generate the energy for the signals from the measuring devices and monitors Control of a 3/2-way solenoid valve 11 to deliver, which controls the hydraulic working medium of a spindle piston generally designated 24. The pump 10 is secured via a pressure relief valve 12 in the ring line 13 to the tank 14, from which it is supplied with pressure medium. The solenoid valve receives its control currents from an electronic control 16. This receives the signals from the measuring devices or monitors 17, 18. In addition to the reproduction of the control variables of the automatic control strip adjustment coming from the inclinometers mentioned, there are signals with which the state of selected devices of the outer tube is monitored. In this way, information can be obtained not only about the direction of the bore, but also about the technical condition of the target boring bar 2. Specifically, it can be measurement data that report wear, impending failure of the hydraulic system or the electrical or electronic control elements in good time. The corresponding adjustment of the solenoid valve 11 ensures a selected pressurization of the spindle piston.

According to the embodiment in FIGS. 2, 3 and 6, this spindle piston is a double piston, the details of which are explained in more detail with reference to the illustration in FIGS. 2 and 3. Accordingly, the spindle piston is seated in a recess 44, which has the same diameter over the greater part of its length and passes through the inner tube 4 and the flushing channel 3 (FIG. 2). During the face piston 45, which with an O-ring 46 in one half 47 of the spindle piston recess 44 is sealed, is acted upon directly from a line 21b, the short piston 49, which is offset by the shaft 48, is mounted in one half 50 of the spindle piston recess 44 and sealed with an O-ring 51 therein. The recess extends up to an annular seat 52 for a helical spring 26. An axial transverse bore 53 forms a hydraulic connection to the outside. The helical spring 26 is supported under the shirt 54 of the short piston 49 and on a pin 55 extending from the bottom of the short piston 49 and protruding from the piston skirt 54. The spindle shaft 48 constantly traverses the flushing channel 3, which is only slightly throttled because of the small spindle shaft, ie the piston shaft is significantly less than the piston diameter.

The embodiment of the spindle piston 24 'according to FIG. 8 differs from this. Although the recess 44 is provided with a section for the end piston 45, the full diameter ends before the flushing channel 3 on the annular shoulder 52, which forms the seat of the helical spring 26 and continues with a small diameter in the half 50, but which is greatly shortened to accommodate the free end 56 of the spindle shaft 48, which does not cross the flushing channel continuously, but only when the piston end face 57 is pressurized, when the force of the coil spring 26 is overcome ^* will.

3, the forwarding of the hydraulic working medium for the actuation of the spindle piston 24 from the stationary Outer tube 5 is shown on the rotating inner tube 4 in the recess of the spindle piston, which is generally designated 24. Then, in front of the bearing pairs 58 and 59 of the outer tube on the drilling tool, there is a sleeve 60 on the inner tube, which is locked against rotation with the inner tube by means of a pin 61 and carries an annular groove 62, 63 on its outside for pressurizing or relieving the pressure on the spindle piston 24. The two ring grooves 62, 63 are hydraulically sealed on the outside by ring seals 64, 65, 66 and on the inside by ring seals 67, 68, 69 and on the outside. With the help of radial bores 70 and 71, they are connected to the channels in the outer tube, which form the forward and return lines 13, 19 and 20 for the hydraulic working medium.

When the solenoid valve 11 is actuated and the corresponding channel 21a or 21b is acted upon or relieved, the pressure medium is either guided in front of the end face 22 of the spindle piston and displaced from the space behind the end face 23 of the short piston 49, so that the spindle piston is instantaneously deflected or the action is reversed, whereby the spindle piston is immediately returned to its starting position.

When the spindle piston 24 is deflected, the flushing flow through the flushing channel is instantly severely throttled with the help of the advancing front piston 45, or completely shut off for a short time. This results in a steep increase in pressure in the rinsing channel, which after switching the solenoid valve 11 also one leads to a steep pressure drop because the spring 26 immediately returns the piston to its starting position. This results in rectangular pressure pulses, which are shown at 35 in FIG. 5. The double arrows drawn above these pulses represent the pulse duration, which is given by the pressure increase and pressure drop until the following pressure pulse. This pulse duration identifies a measured value and a measured signal. It is picked up by a converter 29 and converted into a voltage value.

The further pulse train 36 represented by 35 in FIG. 5 with its pulse duration also represented by double arrows identifies a different measurement signal, so that the spindle piston via the directional control valve 11 due to the high switching frequency achievable with solenoid valves of this type actually a multitude of measured values in perfectly distinguishable Record pressure signals and impress the flushing current. can. The converter designed as a differential pressure sensor 29 can therefore convert these pressure signals into electrical signals that can be identified.

For example, in FIG. 4 the control station 28 is provided with the converter designed as a differential pressure sensor 29, which actuates a display device 30 and, if appropriate, a writing device 31 at the same time. The converter 29 is accommodated in the drilling slurry feed 33 to the flushing channel. The display device can also be arranged at a distance from the control station 28, possibly also above ground, since the converter 29 supplies current pulses on the output side.

• Der Generator 8 ist ein Langsamläufer von 60 U/min und liefert trotz der geringen Umdrehungszahl eine Wechselspannung von 3 ≈ von 24 Volt bei einer erforderlichen Leistung von rd. 40 Watt. Anstelle eines Wechselstromgenerators 8 lassen sich auch zwei Gleichstrommotoren verwenden.

Using the example of FIG. 3, a possible dimensioning for a target boring bar used for a borehole diameter 8 1/2 "can be specified, which is described below:

• The generator 8 is a slow-running machine of 60 rpm and, despite the low number of revolutions, supplies an alternating voltage of 3≈ of 24 volts with a required power of approx. 40 watts. Instead of an alternating current generator 8, two direct current motors can also be used.

The electronics has a power section, which includes a rectifier, which converts the three-phase current into direct current and also has a voltage regulator for maintaining the 24 volt voltage. A voltage converter DC-DC provides - 12 V = for measuring around a zero point. In addition to the power electronics, there is control electronics. It consists of a frequency generator for supplying the direction sensors, a rectifier that directs the direction signals, a target-actual value comparator (window) for the control described at the outset and a control of the solenoid valves that release the oil flow to the control piston of the control bar actuation.

In addition to the power and control electronics described, transmitter electronics are provided for recording and forwarding measured values or signals which come from guards. In particular, it is a matter of passing on the signals from the two inclinometers for e.g. B. vertical holes, which are transmitted via a control voltage of - 5 V. In addition, the temperature z. B. the hydraulic medium is monitored at two points, which is done by a voltage signal of 0 to 5 V. The hydraulic tank pressure from 0 to 5 bar can also be reproduced with a voltage signal from 0 to 5 V. The hydraulic system pressure from 0 to 100 bar, which is limited to this value, is also displayed with a voltage of 0 to 5 V =, while the hydraulic pressure in the measured value transmission system from 0 to 60 bar (spindle piston) is limited to this value and with 0 up to 5 V _{= is} transmitted. Finally, the generator voltage of 18 to 38 V can be monitored in this way.

For the eight monitoring systems described, which could also be increased or decreased if necessary, eight channels are therefore required for the transmission of the measurement data as shown at 35 and 36 in FIG. 5. In the transmitter electronics 16, which includes the actual transmitter, The eight measured values must therefore be recorded as voltage values ^± 5 V or 0 to 5 V and the voltage-time conversion of the measured values must be carried out. The transmitter electronics must form pulses from this, the pulse duration, ie the time interval between two successive pulses, corresponding to the voltage value of a measured value channel (8 channels → 9 pulses). In the transmitter electronics, the measured values at the input are queried cyclically and, for the 8 channels → 9 pulses, are output serially to an output transistor which actuates the solenoid valve 11 for the spindle piston at the appropriate time interval (9 pulses). By actuating the pulse piston, the flushing sludge column in the drill pipe modulates the pressure pulses that are received by the differential pressure sensor 29 at the drilling rig outside the borehole. With a sensitivity of the differential pressure sensor of 0 to 100 mbar and with a voltage supply of 10 to 40 V, current pulses of 0 to 20 mA can be obtained on the output side. These can be forwarded by the converter 29 via a two-wire cable, regardless of the line length.

Eight channels with a voltage supply of 24 V can be provided on the receiver side. In the receiver, the remotely transmitted current pulses are converted into voltage pulses and recorded serially. The receiver evaluates the time intervals between the pulses and converts them into voltage values. The voltage values correspond to the measured values recorded by the transmitter. The output is made in parallel on eight digital displays.

To detect the pulses emitted by the transmitter by the receiver, two synchronous pulses are additionally generated before each series of measurements (nine pulses). The time interval between these synchronizing pulses is always the same. This means that the transmitter and receiver are synchronized. The measurement pulses are only recorded after the receiver has correctly received these synchronization pulses. This enables transmission errors to be eliminated.

The transmission accuracy is ± 1.5 V at ± 5 V → 156 mV ≙. For the inclination with a measuring range of ± 1 °, this means a transmission error of - 1 arc minute, which corresponds to the measuring accuracy of the previously used and known inclinometers.

According to the embodiment shown in FIG. 9, the diameter of the recess 44 for the spindle piston is larger than the diameter of the flushing channel 3, which is arranged in the projection of the recess. The spindle piston has a recess 72 which has the same outline and cross section as the flushing channel. A groove 73 in the wall of the recess 44 cooperates with a cam 7 ₄ on the piston 24, so that the piston is fixed over its entire distance about its longitudinal axis and the neutral position of the piston is flush with the flushing channel. As a result, in this embodiment of the invention, the spindle shaft 48 is limited to the remaining cross section of the spindle piston in the region of its recess 72 and is therefore outside the flushing channel cross section. In this way, the flushing channel cross section remains unrestricted in the neutral position of the piston.

Claims (10)

1. Target boring bar for rotating drill pipe with flushing channel, preferably for underground operation, in which an inner pipe driven by the drill pipe is arranged concentrically in the standing outer pipe, which has a pressure generator for a hydraulic control circuit accommodated in the target boring bar, the movable part of which is formed by the inner pipe or by one Electric motor is driven, the drive of which is derived from the inner tube, whereby measured values from measuring devices accommodated in the outer tube are transmitted from the borehole to the control station by means of a telemetric device, characterized in that the telemetric device which is known per se is the one through the flushing channel (3 ) running flushing flow and a hydraulic converter, which converts the measured values into pressure pulses of the flushing, and that the converter has a spindle piston (24) for which a recess penetrating the inner tube (4) and the flushing channel (3) radially (44) is provided, the spindle piston (24) which is guided and sealed with at least one piston (45, 49) on one side or on both sides of the flushing channel (3) in the piston recess (44) with its shaft (48) the flushing channel ( 3) crosses and is acted upon on one or both sides with the medium of the hydraulic control circuit. 2. Target boring bar according to claim 1, characterized in that the spindle piston (24) is supported on one side on a spring (26) which is located on the underside of a piston (45), the piston recess (44) and on which the flushing channel (3) traversing spindle shaft (48) or a coaxial piston pin (55) is supported on the piston side (49) opposite the spindle shaft (48), the end face of the spring (26) facing and opposite to it being able to be acted upon by a 2/3 directional solenoid valve. 3. Target boring bar according to one of claims 1 or 2, characterized in that the piston recess (44) is covered by a rotating sleeve (60) which has on its outside against one another and against the inner jacket of the outer tube sealed annular grooves (62, 63), which are connected via cross bores (70, 71) in the sleeve (60) to the piston recess (44) and cross bores in the outer tube with a directional valve (11). 4. Target boring bar according to one of claims 1 to 3, characterized in that both the inclinometer (17) and the direction indicator (18), temperature, pressure and voltage meter serve as measuring transducers (17, 18), in groups or individually at different points of the outer (5) or inner tube (4) are arranged. 5. Zielbohrstange according to any one of claims 1 to 4, characterized in that the ear stood at _B (28) disposed evaluation unit is a differential pressure sensor (29) which is coupled to a display device (30). 6. Target boring bar according to one of claims 1 to 5, characterized in that the boring bar generator (8) is equipped with a rectifier and voltage regulator and voltage converter and supplies the electronic control (16) with an associated transmitter in terms of energy. 7. Target boring bar according to one of claims 1 to 6, characterized in that the receiver of the differential pressure transducer (29) and the transmitter of the electronic control (16) are synchronized and switched so that the synchronization is checked before this series of measurements. 8. Target boring bar according to one of claims 1 to 7, characterized in that at least one magnetically balanced magnetometer serves as an inclinometer (17) at least one electronically supported accelerometer and as a direction indicator (18). 9. Target boring bar according to one of claims 1 to 8, characterized in that the outer tube (5) is assigned one or more gamma-ray sensors. 10. Target boring bar according to one of claims 1 to 9, characterized in that the shaft (48) associated with the flushing channel (3) of the spindle piston (24) is arranged outside the flushing channel cross section.

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