HK1018298A - Trenchless underground boring system with boring tool location - Google Patents

Description

Trenchless underground drilling system capable of positioning drilling tool

Technical Field

The present invention relates generally to the field of trenchless subterranean drilling and, more particularly, to a system and method for acquiring positional data of a subterranean drilling tool for controlling the subterranean drilling tool based on the positional data and for obtaining characteristics of the subterranean medium through which the tool is drilled.

Background

For safety and aesthetic reasons, water, electricity, gas, telephone and cable television utility lines are often run underground. In many instances, underground utilities may be buried in trenches and the trenches then backfilled. Although useful in new construction areas for burying facilities in trenches, this has some disadvantages. In areas supporting existing buildings, the trenches can cause severe disturbances to the structure and the roadway. Furthermore, previously buried facilities are highly likely to be damaged by trenching, and structures and roads disturbed by trenching are rarely restored to their original state. Furthermore, the grooves present a risk of injury to workers and passers-by.

To overcome the above disadvantages and other problems that have not been solved when using conventional trenching techniques, general techniques for drilling horizontal subterranean holes have recently been developed. According to this general horizontal drilling technique, also known as micro-tunneling or slotless underground drilling, a drilling system is provided on the ground surface and drilled into the ground at an oblique angle with respect to the ground. To remove the cutting debris and ballast, water flows through the drill string, through the boring tool, and back to the surface from the borehole. After the boring tool reaches the desired depth, the tool is then oriented along a substantially horizontal path to create a horizontal bore. After the desired borehole length is obtained, the tool is oriented upward through the ground. A reamer is then secured to the drill string and the drill string is pulled back through the borehole, thereby enlarging the borehole to a larger diameter. The utility wire or catheter is typically attached to the reaming tool so that it is pulled through the borehole with the reamer.

Such a general method of trenchless drilling has been described by Geller et al (U.S. patent 4,787,463) and Dunn (U.S. patent 4,953,638). Methods of steering an underground boring tool are disclosed in these patents. To provide a location of the boring tool in the subsurface, Geller discloses: active beacons (active beacons) in the form of a radio transmitter are introduced into the boring tool. The position of the tool is determined by radio direction finding (radio direction finding) using a receiver located at the surface. However, because there is no synchronization between the beacon and the detector, the depth of the tool cannot be measured directly, and thus the measurement of the position of the boring tool is limited to a two-dimensional surface plane. However, the depth of the boring tool can be determined indirectly by measuring the water pressure at the boring tool, but this process requires stopping the boring operation. Furthermore, the radio direction finding techniques described in the prior art have limited accuracy in determining the position of the boring tool. These limitations can have serious consequences when drilling trenchless underground in areas containing some existing underground utilities or other natural or man-made obstructions, as the location of the boring tool must be accurately determined in such cases to avoid accidentally disturbing or damaging the utilities.

Investigation along a predetermined grooveless borehole path is done using permeable underground radars (GPR), applications of which have been identified by kathrag (fourth international conference corpus of underground penetrating radars, finland geological survey, monograph 16, "a challenge: GPR horizontal borehole front", page 119-. However, the GPR image information obtained during the survey described in these publications is only applicable to a limited extent, for example by adding these image information to the survey database or by performing some limited operation on the survey database.

Subsurface penetrating radar is a sensitive technology in detecting even small changes in the subsurface dielectric constant. As a result, the image produced by the GPR system contains a great deal of detail, a lot of which is undesirable or unnecessary for the task at hand. Therefore, a major difficulty in using GPR to locate a boring tool is the inability in the prior art to properly distinguish the boring tool signal from all signals generated by other features, collectively referred to as clutter (clutter). In addition, depending on the depth of the boring tool and the propagation characteristics of the intermediate subsurface medium, the signal from the boring tool can be particularly weak relative to this clutter. As a result, the boring tool signal is either misinterpreted or even not detected.

It is desirable to position the downhole drilling tool in three dimensions with a device, such as a GPR system, with a precision that is higher than is available in the current state of the art. However, for the reasons described above, there has not been a slot-less drilling system that provides a highly accurate location of an underground boring tool.

Summary of The Invention

The present invention relates to an apparatus and method for locating an underground boring tool using radar-like detectors and detection techniques. Means are provided for the boring tool to generate a specific signature in response to a probe signal emitted from the surface. The combined action between the probe signal transmitter at ground level and the signature signal generating means provided in the underground boring tool allows accurate detection of the boring tool even in the presence of large background signals. Accurate inspection of the boring tool allows the operator to accurately position the boring tool during operation and also avoids concealed obstructions, such as utilities and other obstructions, if directional capabilities are provided. The detection signal may be a microwave or an acoustic wave.

The characteristic signal generated by the boring tool may be passive or active. Furthermore, the signature signal may be generated in a manner that differs from the detector in one or more aspects, including timing, frequency content, or polarization characteristics.

According to one embodiment, a survey is conducted of a borehole site prior to or during a drilling operation to provide data relating to characteristics of the subsurface medium under investigation. Subsurface property data obtained during the survey is correlated against (existing) historical data that relates subsurface type to borehole productivity, thereby enabling the borehole productivity and total cost at the survey site to be estimated. An accurate survey of the planned drilling path is possible and the position of the drilling tool during the drilling operation can be accurately measured for comparison with the planned path at the time or thereafter. The orientation of the boring tool can be adjusted according to the measured position in order to keep the boring tool boring along the planned path.

Brief Description of Drawings

FIG. 1 is a side view of a slotless subterranean drilling apparatus according to one embodiment of the present invention;

FIG. 2 is a side detailed schematic view of the slotless subterranean drilling tool of FIG. 1 and a sonde and detection unit;

FIG. 3 is a graph depicting the generation of a signature signal in the time domain;

FIG. 4 is a graph depicting the generation of a signature signal in the frequency domain;

FIG. 5 shows three embodiments for generating a passive microwave signature;

FIG. 6 shows four embodiments for generating an active microwave signature;

FIG. 7 illustrates two embodiments for generating an active acoustic signature;

FIG. 8 shows an embodiment of a borehole tool including an active microwave signature generator;

FIG. 9 is an illustration of sampling a concealed target for reflected signals received by a subsurface penetration radar system using a single axis antenna system;

FIG. 10 is an illustration of a conventional single axis antenna system typically used with a subsurface penetration radar system to provide two-dimensional subsurface geological imaging;

FIG. 11 is an illustration of a novel antenna system including a plurality of antennas oriented in an orthogonal relationship for use with a subsurface penetrating radar system to provide three-dimensional subsurface geological imaging;

FIG. 12 is an illustration of a borehole site having a non-uniform subsurface geological structure;

FIG. 13 is a system block diagram of a slotless drilling system control unit that integrates a position indicator, a geographic recording system, various databases, and a geological data acquisition unit;

FIG. 14 is an illustration of a drilling site and a slotless drilling system including a positioning device;

FIG. 15 shows in flow chart form the general method steps of a completed pre-borehole survey;

FIG. 16 is a system block diagram of a trenchless subterranean drilling system control unit for controlling drilling operations;

FIGS. 17-18 illustrate in flow chart form the general method steps for completing a slot-less drilling operation;

FIG. 19 shows an embodiment of a slotless subterranean drilling tool incorporating various sensors and further depicting signal information from the sensors; and

FIG. 20 shows an embodiment of a slotless underground boring tool including an active beacon and various sensors, and further illustrates signal information of the sensors.

Detailed description of the embodiments

Referring now to the drawings and more particularly to FIG. 1, there is shown an embodiment of a trenchless subterranean drilling system including a detection system for detecting the position of a subterranean drilling tool. Figure 1 shows a section through a subterranean portion 10 where a drilling operation is performed and most of the components of the described detection system above the surface 11. The trenchless underground drilling system, generally indicated at 12, includes a platform 14 upon which is placed a longitudinal member 16 that is inclined. The platform 14 is secured to the ground with pins 18 or other clamping members to prevent the platform 14 from moving during the drilling operation. A push/pull pump 20 is disposed on the longitudinal member 16 for driving the drill string 22 in a forward longitudinal direction, as generally indicated by the arrow. The drill string 22 is made up of a plurality of end-to-end connected drill string components 23. Also located above the inclined longitudinal parts 16 and arranged to allow movement along the longitudinal parts 16 is a rotation motor 19 for rotating the drill string 22 (shown in an intermediate position between the upper position 19a and the lower position 19 b). In operation, the rotary motor 19 rotates the drill string 22 with the boring tool 24 at the end of the drill string 22.

The drilling operation proceeds as follows. The rotation motor 19 is initially in an upper position 19a and rotates the drill string 22. During rotation of the boring tool 24, the rotary motor 19 and the drill string 22 are pushed by the push-pull pump 20 in a forward direction towards a lower position into the ground, thereby creating a borehole 26. When the drill string 22 has been pushed into the borehole 26 for the length of one drill string component 23, the rotary motor 19 has reached the lower position 19 b. A new drill string component 23 is then added to the drill string 22 and the rotation motor is released and pulled back to the upper position 19 a. The rotary motor 19 then grips onto the new drill string component and repeats the rotation/push process, thereby forcing the newly grown drill string 22 further into the ground and lengthening the borehole 26. Typically, water is pumped through the drill string 22 and back through the wellbore to remove cutting chips, ballast and other debris. If the boring tool 24 includes directional capability to control its direction, then a desired direction can be imparted to the resulting borehole 26. The borehole 26 shown in figure 1 is curved around a point 31, from an initial inclined portion to become parallel to the surface 11. A detection and detection unit (PDU)28 is located above the ground surface 11 and can be separate from the trenchless underground boring system 12, with PDU28 being mounted on wheels 29 or rails to allow travel above the ground along a path corresponding to the underground path of the boring tool 24. PDU28 is connected to control unit 32 via data transmission line 34.

The operation of PDU28 may be more clearly described with reference to fig. 2. PDU28 is generally used to transmit probe signals 36 into the ground and detect return signals. PDU28 includes a generator 52 for generating a probe signal 36 for probing subsurface 10. Transmitter 54 receives probe signal 36 from generator 52 and, in turn, transmits probe signal 36 (shown in solid lines in FIG. 2) into subsurface 10. In a first embodiment, generator 52 is a microwave generator and emitter 54 is a microwave antenna that emits a microwave probe signal. In another embodiment, generator 52 is an acoustic generator and generates acoustic waves, and transmitter 54 is typically a probe that is placed into subsurface 10 to ensure good mechanical contact to transmit the acoustic waves into subsurface 10.

Probe signal 36 transmitted by PDU28 propagates underground and encounters an underground obstruction, one of which is shown at 30, which scatters return signal 40 (shown in dotted lines in FIG. 2) back into PDU 28. A characteristic signal 38 (shown in dashed lines in fig. 2) is also returned from the boring tool 24 located in the borehole 26 to PDU 28.

The detection portion of PDU28 includes receiver 56, detector 58, and signal processor 60. Receiver 56 receives return signals from subsurface 10 and transmits them to detector 58. The detector 58 converts the return signal into an electrical signal for subsequent analysis in a signal processing unit 60. In the first embodiment described above, the probe signal 36 is constituted by a microwave signal, the receiver 56 typically comprises an antenna and the detector 58 typically comprises a detector diode. In another embodiment, probe signal 36 is comprised of sound waves, receiver 56 is typically a probe that has good mechanical contact with subsurface 10, and detector 58 comprises an acoustic-to-electrical transducer, such as a microphone. The signal processor 60 may include various primary components such as signal amplifiers and analog-to-digital converters, followed by more complex circuitry to generate two-or three-dimensional images of the subsurface volume including the various subsurface obstacles 30 and the boring tool 24. PDU28 also contains a beacon receiver/analyzer 61 for detecting and interpreting signals from underground active beacons. The beacon receiver/analyzer 61 will be described more fully hereinafter.

Referring again to fig. 1, PDU28 conveys the acquired information along data transmission line 34 to control unit 32, where control unit 32 is shown located near trenchless underground drilling system 12. A data transmission line 34 is provided to carry data transfer between PDU28 and the trenchless underground drilling system 12 and may be a coaxial cable, an optical fiber, a free space link for infrared communication or other suitable data transmission medium.

One significant advantage of using a trenchless underground boring system 12 employing the underground inspection techniques described herein is that the inspection boring tool 24 can purposefully avoid other important underground features, particularly buried utilities such as electricity, water, gas, sewage, telephone lines, cable lines, and the like.

Conventional subsurface imaging techniques, such as subsurface penetrating radar (GPR), which are well known in the art of subsurface imaging, can detect the presence of many types of subsurface obstacles and structures. One major difficulty that remains unresolved by conventional borehole tool detection techniques is the inability to distinguish borehole tool signals from the many return signals (collectively clutter) that accompany other subsurface obstructions and structures. Clutter signals constitute background noise, above which the borehole tool signal must be distinguishable. It will be appreciated that the return signal from the boring tool 24 may be weak compared to the clutter signal, in other words a signal-to-clutter ratio (signal-to-clutter ratio) is low, thereby reducing the ability to clearly identify the boring tool signal. The detection and detection apparatus and method of the present invention is advantageous in that a boring tool return signal is provided having a characteristic signature that can be more easily distinguished from clutter signals. The generation of the characteristic signal can be effected passively or actively. The generation of this characteristic signal is illustrated in fig. 3 and 4, according to one embodiment.

FIG. 3 is a diagram depicting the generation and detection of boring tool signature signals in the time domain. Line a represents the emission of a probe signal 36a as a function of signal plotted against time. Line B represents the return signal 62a detected by PDU28 without generating any signature signal. The return signal 62a depicts the signal received by PDU28 at a time at 1 after the probe signal 36a was transmitted and appears as a mixture of return signals from the boring tool 24 and other scatterers. As discussed previously, the low signal-to-noise ratio makes it difficult to distinguish the signal returned by the boring tool. Line C shows an advantageous detection technique in which the joint operation between the boring tool 24 and PDU28 is used to generate and transmit a boring tool signature signal at a time Δ T2 after the probe signal 36a is transmitted. In accordance with this detection scheme, the return signal 40a received from the scatterers is first detected, and the signature signal 38a received from the boring tool 24 is detected after a delay of Δ T2. The delay time Δ T2 is set long enough so that the boring tool signature signal is significantly more prominent than the other clutter signals at the time of detection. In this case, the signal-to-noise ratio of the boring tool signature 38a is relatively high, so that the signature 38a can be readily distinguished from the background clutter 40 a.

FIG. 4 depicts detection of a characteristic signal of a boring tool in the frequency domain. Line a represents the frequency band 36b of the probe signal as a function of signal strength versus frequency. Line B represents the frequency band 62B of the return signal from the boring tool 24 without producing any joint signal. It can be seen that the signals returned from the boring tool 24 and other scatterers 30 together occupy the same frequency band 62b as the probe signal 36 b. Line C represents the case where co-operation between the boring tool 24 and PDU28 is utilized, thereby generating and transmitting a boring tool signature signal having a frequency band 38b different from the scattered return signal frequency band 40 b. The band difference, denoted by Δ f, is large enough to shift the characteristic signal of the boring tool out of the scattered return signal band 40 b. Thus, the characteristic signal of the boring tool can be detected relatively easily due to the increased signal-to-noise ratio. It should be noted that high-pass or low-pass filtering techniques or other similar filtering methods may be utilized to enhance the detection of the boring tool signature signal.

It is an important feature of the present invention that the boring tool 24 includes a signature generation device that generates a signature in response to receiving the probe signal from the PDU 28. It is difficult, if not impossible, to distinguish this echo from the clutter signal with high certainty using conventional detection techniques. The benefit of incorporating the signature generation means is to provide a unique signal generated by the boring tool 24 which can be readily distinguished from the clutter signal and which has a high signal to clutter ratio. As briefly discussed above, either active or passive methods are suitable for generating the combined signature. An active signature circuit is one in which the circuit used to generate the signature signal requires the application of a power source (e.g., a battery) from an external source to enable its operation. Whereas a passive circuit is a circuit without an external power supply. The energy source of the electrical signal present in the passive circuit is the received probing signal itself.

According to the passive approach, the boring tool 24 does not include active devices that generate or amplify the signal, and is therefore a simpler approach because it does not require the presence of a power source or electronic circuitry in the head of the boring tool 24. Active methods, on the other hand, can be utilized, which have the advantage of being more flexible and can provide the opportunity to generate a wider range of characteristic response signals that are more discernable as the borehole passes through different types of subsurface media. Furthermore, the active approach may reduce the complexity and cost of the signature receiving device.

Three embodiments of passive signature generation devices associated with microwave borehole tool detection techniques are shown in FIG. 5. Each of the embodiments shown in fig. 5 includes a schematic diagram of a boring tool 24 including a microwave antenna and circuit components for generating a characteristic signal. The three embodiments shown in fig. 5a, 5b and 5c are directed to the generation of the characteristic signal using a) the time domain, b) the frequency domain and c) the cross polarization, respectively. In fig. 5a, the boring tool head 64a is shown to include two antennas, a probe signal receiving antenna 66a and a signature signal transmitting antenna 68 a. For purposes of illustration, these antennas are shown as separate elements, but it should be understood that the microwave transmit/receive system can use a single antenna for both receive and transmit operations. The use of two separate antennas in the illustrations of this and subsequent embodiments is intended only to enhance the understanding of the present invention and is not intended to suggest any limitation as to the invention. In a practical implementation of the signature generator, the receiving antenna 66a and the transmitting antenna 68a are preferably located inside the boring tool or placed on the surface of the boring tool in a conformal configuration. With respect to the antenna located within the boring tool 24, it will be appreciated that at least a portion of the boring tool 24 is formed of a non-metallic material, preferably a hard dielectric material, to allow microwaves to enter the boring tool 24 from the subterranean medium 10. One suitable material for this application is KEVLAR.

Fig. 5a shows a characteristic signal generating device for a microwave detection system operating with time-threshold. According to the present embodiment, receiving antenna 66a receives a probe signal 70a from PDU28, such as a short microwave pulse lasting a few nanoseconds. To distinguish the signature signal 74a from the clutter received by PDU28, the received probe signal 70a is transmitted from the receive antenna 66a to a delay waveguide 72a, preferably a coaxial cable, to the transmit antenna 68 a. Signature signal 74a then radiates outward from transmit antenna 68a and is received by PDU 28. A delay line is used which preferably delays the response from the boring tool 24 by about 10 nanoseconds, thereby delaying the transmission of the returned signature signal 74a until after the clutter received by PDU28 has been reduced in amplitude.

According to another embodiment, a single antenna embodiment of the passive time domain signature generator can be realized by severing the waveguide at the point indicated by the dashed line 76a to form a termination. In this latter embodiment, probe signal 70a propagates along waveguide 72a until it is reflected by the terminal at cut-off point 76a, passes back to receive antenna 66a, and is transmitted back to PDU 28. This termination may be implemented as an electrical short, in which case the probe signal 70a will invert in phase when reflected; or as an open circuit in which case the probe signal 70a does not fall over upon reflection.

The introduction of the time delay causes the signature signal 74a to appear to be deeper than its actual position for the boring tool 64 a. Since microwaves are strongly attenuated by the subsurface, the typical effective depth range for subsurface penetrating radar systems is about 10 feet, beyond which point the return signal is strongly attenuated and cannot be reliably detected. The time delayed signature signal 74a returned from the boring tool 64a artificially transforms the depth of the boring tool 24 to an apparent depth in the range of 10 to 20 feet from which no strong signal is returned, thus significantly enhancing the signal to noise ratio of the detected signature signal 74 a.

Fig. 5b shows a characteristic signal generating device for a microwave detection system operating in the frequency domain. According to this embodiment, the receiving antenna 66b in the boring tool 64b receives the microwave probe signal 70b from the PDU 28. The probe signal 70b is preferably a microwave pulse lasting a few microseconds, with a center frequency at a given frequency f and a bandwidth Δ f1, where Δ f1/f is typically less than one percent. To shift the returned signature signal 74b out of the frequency range of the clutter received by PDU28, the received probe signal 70b propagates from the receive antenna 66b along waveguide 72b into a nonlinear electrical device 78b (preferably a diode) that generates resonant signals, such as the second and third harmonics, from the original signal. This harmonic signal is then transmitted from transmit antenna 68b as signature signal 74b and received by PDU 28. PDU28 is tuned to the harmonic frequency of detection probe signal 70 b. For example, for a probe signal 70b of 100MHz, the second harmonic detector would be tuned to 200 MHz. Typically, the response characteristics of the scatterers are linear and only clutter at the frequency of the probe signal 70b is generated. Since no other source of harmonic frequencies is typically present, the signal-to-noise ratio of the signature signal 74b at this harmonic frequency is relatively high. A passive frequency domain embodiment using a single antenna may be implemented by cutting the waveguide at the point shown by dashed line 76b to form a termination, in a manner similar to that discussed above for the passive time domain embodiment. According to this latter embodiment, probe signal 70b will propagate along waveguide 72b, pass through nonlinear element 78b, reflect at terminal 76b, pass back through nonlinear element 78b, pass back to receive antenna 66b, and be transmitted back to PDU 28. As discussed above, the polarity of the reflection will depend on the nature of the terminal.

Figure 5c shows the generation of a signature signal in a microwave detection system operating in a cross-polar mode. In accordance with this embodiment, PDU28 generates a particular linearly polarized probe signal 70c, which is then transmitted into the ground. Clutter signals are formed from the signal returned by scatterers, which generally maintain the same polarization direction as probe signal 70 c. Thus, the clutter signal has substantially the same polarization as the probe signal 70 c. In the drilling tool 64c, a characteristic signal 74c is generated in such a way that: the polarized probe signal 70c is received in the receive antenna 66c, propagates through the waveguide 72c to the transmit antenna 68c, and transmits the signature signal 74c back to the PDU 28. Transmit antenna 68c is oriented such that the polarization of radiated characteristic signal 74c is orthogonal to the polarization of received probe signal 70 c. PDU28 may also be configured to preferentially receive signals having a polarization direction that is orthogonal to the polarization direction of probe signal 70 c. In this way, the receiver 56 preferentially detects the feature signal 74c over the clutter signal, thus improving the signal-to-noise ratio of the feature signal.

The termination is formed by cutting the waveguide at the point shown by dashed line 76c, in a manner similar to that discussed above for the passive time and frequency domain embodiments. And inserting a hybrid 78c that changes the polarization direction of the passing wave, cross-polarization embodiments using a single antenna can be realized. In this latter embodiment, the probe signal will propagate along waveguide 72c, pass through polarization mixer 78c, reflect at terminal 76c, pass back through polarization mixer 78c, pass back to receive antenna 66c, and be transmitted back to PDU 28. The polarity of the reflection may be determined by the nature of the termination, as discussed above. It should be appreciated that the antenna employed in this single antenna embodiment should have good enough radiation characteristics for orthogonal polarizations. It should also be understood that cross-polarized embodiments may utilize circularly or elliptically polarized microwave radiation. It will also be appreciated that the cross-polarization embodiment may be used in conjunction with the passive time domain or passive frequency domain signature signal generating embodiments described above with reference to fig. 5a and 5b to further enhance the signal-to-noise ratio of the detected signature signal.

Referring now to fig. 6, an active signature generation embodiment will be described. FIG. 6a shows an embodiment of generating active time domain signature signals suitable for inclusion in a boring tool 80 a. The illustrated embodiment of generating active time domain signature signals included in the boring tool 80 a. The illustrated embodiment shows probe signal 82a being received by a receive antenna 84a, the receive antenna 84a being coupled to a delay line waveguide 86 a. An amplifier 88a is located at a point along waveguide 86a and amplifies probe signal 82a as it propagates along waveguide 86 a. The amplified probe signal continues to propagate along delay line waveguide 86a to transmit antenna 90a, which in turn transmits this signature signal 92a back to PDU 28. Fig. 6b shows another embodiment of an active time domain signal generator that includes a triggerable delay circuit to generate a time delay, rather than having the signal propagate along a long delay waveguide. The illustrated embodiment shows probe signal 82b being received by a receiving antenna 84b coupled to a waveguide 86 b. The triggerable delay circuit 88b is located at a point along the waveguide 86 b. The triggerable delay circuit 88b operates as follows: triggerable delay circuit 88b is triggered by probe signal 82b, which starts an internal timer circuit upon initial detection of probe signal 82 b. Once the timer circuit has reached the predetermined delay time, preferably in the range of 1-20 nanoseconds, the timer circuit generates an output signal from the triggerable delay circuit 88b which is used as the characteristic signal 92 b. This signature signal 92b propagates along waveguide 86b to transmit antenna 90b, which then transmits signature signal 92b to PDU 28.

Figure 6c shows an embodiment of an active frequency domain signature generator suitable for inclusion in a boring tool 80 c. The illustrated embodiment shows probe signal 82c being received by a receiving antenna 84c coupled to a waveguide 86c and a nonlinear element 88 c. The frequency-shifted signal produced by the nonlinear element 88c then passes through an amplifier 94c before being passed to a transmit antenna 90c, which sends the characteristic signal 92c to a PDU 28. The advantage of using an active frequency domain signature generator embodiment over a passive frequency domain signature generator embodiment is that the active embodiment generates a stronger signature signal, which is easier to detect.

In a second embodiment of the active frequency domain signature generator, generally shown in fig. 6c, the probe signal 82c passes through an amplifier 94c before reaching the nonlinear element 88 c. The advantages of this further embodiment are: the amplifier can be implemented at a lower cost since the amplification process can be performed at a lower frequency.

A third embodiment of an active frequency domain signature generator suitable for use in a boring tool 80d is shown in figure 6 d. Fig. 6d shows the receive antenna 84d coupled to the frequency shifter 88d and the transmit antenna 90d using the waveguide 86 d. The frequency shifter 88d is a device that produces an output signal 92d having a frequency f2 that is different from the frequency f1 of the input signal 82d by half the bandwidth of 82d, typically on the order of 1 MHz. The frequency shifter 88d produces a sufficient frequency shift to shift the signature signal 92d out of the clutter signal band, thereby enhancing the signal-to-noise ratio of the detected signature signal 92 d. For the purposes of describing these embodiments, the term "signature" encompasses all generated return signals from the borehole tool 24 except for the natural reflection of the probe signal from the borehole tool 24.

FIG. 7 shows one embodiment of a signature generator suitable for use in a boring tool 96, wherein the probe signal is an acoustic signal. In the sonic time domain embodiment shown in FIG. 7a, a sonic probing signal 98a (preferably a sonic pulse) is received and detected by a sonic receiver 100a mounted on the inner wall of the boring tool 96 a. The acoustic receiver 100a transmits a trigger signal along trigger line 102a to delay pulse generator 104 a. After being triggered, the delay pulse generator 104a generates a characteristic pulse after the trigger delay. This characteristic pulse is transmitted along transmission line 106a to sonic transmitter 108a, which is also mounted on the interior wall of boring tool 96 a. Acoustic transmitter 108a then transmits the acoustic signature signal through the subsurface for detection by PDU 28.

In accordance with the sonic frequency domain embodiment shown in FIG. 7b, a sonic pulse having a given sonic frequency f3 is preferably received and detected by a sonic receiver 100b, which sonic receiver 100b is mounted on the interior wall of the boring tool 96 b. Sonic receiver 100b transmits an input electrical signal having a frequency f3 corresponding to received sonic signal 98b along receive line 102b to frequency shifter 104 b. Frequency shifter 104b produces an output electrical signal having a frequency shifted by Δ f3 relative to the frequency of input signal 98 b. The signal output from the frequency shifter 104b is transmitted along transmission line 106b to an acoustic transmitter 108b, which is also mounted on the inner wall of the boring tool 96 b. Acoustic transmitter 108b then transmits the shifted acoustic signature 110b through the subsurface for detection by PDU 28.

Fig. 8 shows an apparatus for actively generating a signature signal in an underground boring tool 24. The head of the boring tool 24 is shown. At the forward end of the boring tool 24a is a cutter 120 for cutting soil, sand, clay, and the like when forming an underground passageway. The cut away portion 122 of the boring tool wall reveals a circuit board 124 that is designed to fit inside the boring tool 24 a. A battery 126 is attached to the circuit board 124 for providing power. An antenna 128 is also connected to the circuit board 124 for receiving the incoming probe signal 36 and transmitting the foreign row signature signal 38. The antenna 128 may be located inside the boring tool 24a, or may be a conformal design that is located on the surface of the boring tool 24a and conforms to the surface profile. The boring tool 24a may also include one or more sensors for detecting the environment of the boring tool 24 a. Circuitry is provided in the boring tool 24a for relaying this environmental information to a control unit 32 located on the earth. For example, the sensors may be used to measure the orientation (pitch, yaw, roll) of the boring tool 24a or other factors, such as the temperature of the cutting tool head or the water pressure at the boring tool 24 a.

In fig. 8, a sensor 130, such as a pressure sensor, is shown positioned behind the cutting tool 120. Electrical connections 132 lead from the sensor 130 to the circuit board 124, which contains circuitry for analyzing signals received from the sensor 130. The circuit board 124 may modulate the signature signal 38 to contain information about the sensor output, or may generate a separate sensor signal that is thereafter detected and analyzed at the surface.

As is known in the art of subsurface imaging, a single sweep of a portion of the subsurface by a GPR unit can produce two-dimensional data when GPR utilizes a single transmitter and receiver. Figure 9 shows a graph of GPR system data obtained for a sample test site with 5 different man-made barriers buried in sand to a depth of about 1.3m with the water table at a depth of about 4 to 5 m. It should be noted that the data shown in FIG. 9 represents typical data acquired using a conventional single axis antenna centered at 450MHz using a Pulse EKKO 1000 system manufactured by Sensors and Software Inc. Other GPR Systems that may be suitable for this application include SIR Systems 2 and 10A manufactured by geophysics survey Systems Inc and subsurface penetration radar of the 1000B STEPPED-FM type manufactured by GeoRadar Inc.

Figure 9 shows that each underground buried obstruction has a characteristic time-location hyperbola associated with it. The apex of the characteristic hyperbola may provide an indication of the location and depth of the buried obstacle. As can be seen from the view on fig. 9, each obstacle is buried at a depth of about 1.3m below the ground, and each obstacle is spaced from the adjacent obstacle by a horizontal distance of about 5 m. The GPR system shown in fig. 9 represents geological imaging data acquired using a conventional single axis antenna system, thus providing only a two-dimensional representation of the subsurface objects being probed. As will be discussed below, multiple antenna structures arranged in orthogonal orientations may provide an enhanced three-dimensional view of the subsurface geology associated with a particular borehole site.

The two-dimensional data of fig. 9 is a displayed plurality of images that graphically represent the depth versus position of the object along the lateral direction. In order to obtain three-dimensional data, the GPR system using a single axis antenna must perform several sweeps over the underground portion, or else multiple antennas must be used. The following describes the use of GPR to construct two-dimensional and three-dimensional images. Two-dimensional and three-dimensional images were constructed using GPR.

In fig. 10, a GPR imaged subsurface portion 500 is shown having a buried barrier 502 located within the subsurface portion 500. The ground 504 lies in an x-y plane formed by the x and y axes, while the z axis is directed vertically into the ground 500. Typically, multiple survey paths 508 are performed using a single axis antenna (shown as antenna A506 in the figure and oriented along the z-axis). The multiple survey paths 508 are straight lines parallel to each other and uniformly spaced in the y-direction. The multiple passes shown in fig. 10 are parallel to the x-axis. Generally, the GPR system has the ability to measure time, allowing signals emanating from a transmitter, reflecting off a target, and returning to a receiver to be timed. This is commonly referred to as time-of-flight (TIME-of-flight) technology because it measures the duration of the radar pulse that is in flight between the transmitter and the receiver. This time value can be transformed by calculation into a distance measure representing the depth of the object. These calculations are based on characteristic soil property values (e.g., dielectric constant) determined in the field and the wave velocity through a particular soil type. A simplified technique that can be used when calibrating the depth measurement capability of a particular GPR system is to take a target sample core, measure its depth, and correlate it to the number of nanoseconds required for wave propagation.

After the time function capability of the GPR system provides depth information to the operator, the radar system is moved laterally along a horizontal direction parallel to the x-axis, allowing the construction of a two-dimensional subsurface section. By performing multiple surveys of line 508 in parallel mode at a particular site, a series of two-dimensional images can be accumulated to produce an estimated three-dimensional view of the site, with possible buried obstructions therein. It will be appreciated, however, that the two-dimensional imaging capabilities of conventional antenna structures 506 may miss buried obstructions, particularly when obstructions 502 are parallel to the direction of survey routes 508 and are located between adjacent survey routes 508.

A significant advantage of the geological imaging antenna configuration 520 of the present invention, as illustrated in fig. 11, is that it provides true three-dimensional imaging of the subsurface. A pair of antenna a522 and antenna B524 are preferably placed in an orthogonal configuration to provide three-dimensional imaging of the buried barrier 526. Antenna a522 is oriented along a direction contained by the y-z plane, which is +45 ° with respect to the z-axis. Antenna B524 is also oriented along one direction contained by the y-z plane, but at-45 ° with respect to the z-axis, i.e., its position is rotated 90 ° from the position of antenna a 522. It should be noted that the hyperbolic time-position data profile obtained by a conventional single-axis antenna as shown in fig. 9 may instead be a three-dimensional hyperbolic shape that provides a wide, deep, long three-dimensional image of the detected buried obstruction 526. It should also be noted that a buried obstruction 526 (e.g., drain line) parallel to survey line 528 will be immediately detected by the three-dimensional imaging GPR system. In accordance with one embodiment of the present invention, orthogonally oriented transmit and receive antenna pairs are used in the transmitter 54 and receiver 56, respectively, of PDU 28.

Figure 12 illustrates an embodiment in which a detection system is used to locate the inground drilling tool and acquire the intermediate media characteristics between the drill bit and PDU 28. In this figure, a slotless subterranean drilling system 12 is located on the surface 11 of the earth 10 in the area where drilling operations are to be performed. The control unit 32 is located in the vicinity of the trenchless underground drilling system 12. Subsurface 10 is made up of several different subsurface types, examples of which are shown in fig. 12 being sand (subsurface type (GT 2)) 140, clay (GT3)142 and natural soil (GT4) 144. The passages are generally described as the passage filler (GT1)146 portion. The drill string 22 is shown in fig. 12 in its first position 22c, ending with a boring tool 24 c. PDU28c is shown in position above the boring tool 24 c. PDU28c transmits a probe signal 36c that propagates through the road fill and the subsurface. With the boring tool at position 24c, the probe signal 36c propagates through the road filler 146 and the clay 142. In response, the boring tool 24c generates a signature signal 38c, which is detected and analyzed by PDU28 c. Analysis of the signature signal 38c may provide a measure of the time of flight of the probe signal 36c and the signature signal 38 c. Time-of-flight is defined as the duration of time between the transmission of the probe signal 36c and the reception of the signature signal 38c as measured by PDU28 c. The measured time of flight depends on many factors, including the depth of the boring tool 24c, the dielectric state of the intermediate subsurface media 146 and 142, and any time delays involved in generating the signature signal 38 c. Based on time-of-flight measurements, it is known that any two of these factors can yield a third.

The depth of the boring tool 24c can be independently measured by a mechanical probe or by sensing the water pressure at the boring tool 24c with a sensor 130 located in the boring tool head 24c (as discussed above). For the latter measurement (i.e., water pressure measurement), the drilling operation is stopped and the water pressure is measured. Because the height of the water column above the surface in the drill string 22 is known, the depth of the boring tool 24c can be calculated using known techniques.

For embodiments of the invention using microwave probe signals, the general relationship for calculating depth or dielectric constant from time of flight is:

in the formula (I), the compound is shown in the specification,

TE is the effective time-of-flight, which is the duration of the probe or signature signal through the subsurface process;

TD is the time delay inside the boring tool between receiving the probe signal 36c and the transmitted signature signal 38 c; and

d_jis the thickness, ε, of the jth subsurface type above the boring tool 24c_jIs the dielectric constant of the jth subsurface type at microwave frequencies, and c is the speed of light in vacuum.

For the case where the boring tool is located at position 24c shown in fig. 12, and assuming negligible thickness of the road filler relative to the clay thickness, the relationship of equation (1) is simplified as:

here the subscript "3" represents GT 3. The direct measurement of the time of flight TF and the depth of the boring tool 24c, plus knowledge of any time delay TD, will result in an average dielectric constant e 3 of GT 3. This characteristic may be denoted as GC 3. The importance of knowing the dielectric constant is that it can provide information about the type of soil being characterized and its water content.

Returning again to fig. 12, the boring tool 24 in the illustrated embodiment has been moved from its first position 24c to another position 24 d. The drill string 22d (shown in phantom) has been expanded from its original configuration 22c by adding additional drill string components in the manner previously described. PDU28 has been relocated from its original position 28c to a new position 28d (shown in phantom) in order to be adjacent to boring tool 24 d. Time-of-flight measurements may be performed as previously described using probe signal 36d and signature signal 38d to obtain parameter GC4 representative of the subsurface characteristics of natural soil GT 4. Similarly, subsurface properties GC2 can be obtained from time-of-flight measurements at the location indicated by the letter "e". The continuous derivation of the subsurface characteristics as the boring tool 24d moves through the subsurface produces a subsurface characteristic profile that can be recorded by the control unit 32.

It may be advantageous to accurately record the subterranean path traversed by the boring tool 24. For example, it may be desirable to make an accurate record of where utilities have been buried in order to properly plan future excavations and utility burials and avoid causing undesirable disturbances to such utilities. Borehole mapping may be performed manually by associating the boring tool position data collected by PDU28 with a base reference point; or may be electronically accomplished using a Geographic Recording System (GRS)150, represented generally in fig. 13 as a component of the control unit 32. In one embodiment, the Geographic Recording System (GRS)150 communicates with a central processor 152 of the control unit 32, forwarding the precise location of the PDU 28. Since the control unit 32 also receives information regarding the location of the boring tool 24 relative to the PDU28, the precise location of the boring tool 24 can be calculated and stored in the route record database 154.

According to another embodiment, the geographic location data relating to the predetermined subterranean borehole path is preferably acquired prior to the drilling operation. The predetermined route is calculated from surveys completed prior to the drilling operation. The pre-survey includes GPR sensing and geophysical data to estimate the subsurface types to be traversed for the drilling operation and to determine if there are other facilities and buried obstructions in the proposed borehole path. The result of the pre-borehole survey is a predetermined set of route data (set) that is stored in a planned route database 156. During a drilling operation, a predetermined course data set is loaded from the planned course database 156 to the control unit 32 to provide automated navigational directional control of the boring tool 24 as it cuts its subterranean path. In yet another embodiment, the location data acquired by the GRS150 is preferably transmitted to a roadmap database 158, which adds the borehole path data to an existing database as the drilling operation occurs. Route fill database 158 covers a given drilled site, such as a section of a city street or a golf course, under which various facilities, communication facilities, water service lines or other lines may be buried. The data stored in the roadmap database 158 may thereafter be used to generate survey maps that accurately indicate the location and depth of various utility pipes buried at a particular site. The data stored in the roadmap database 158 also includes information about drilling conditions, subsurface characteristics, and productivity of previous drilling operations, thereby enabling an operator to reference data for all previous drilling operations associated with a particular site.

An important feature of the new system for locating the boring tool 24 is the acquisition and use of geophysical data along the path of the borehole. A logically separate Geophysical Data Acquisition Unit (GDAU)160, which may or may not be physically separate from PDU28, may provide independent geophysical prospecting and analysis. The GDAU160 preferably includes a number of geophysical instruments that provide physical characteristics to the geological structure of a particular borehole site. A seismic mapping module 162 includes an electronic device made up of a plurality of geophysical pressure sensors. A network of these sensors, each placed in direct contact with the earth, is arranged in a particular orientation relative to the trenchless subterranean drilling system 12. This sensor network measures the earth pressure waves generated by the boring tool 24 or some other acoustic source. Analysis of the earth pressure waves received by the sensor network provides a basis for determining the subsurface physical characteristics of the borehole site and for locating the boring tool 24. These data are preferably processed by the GDAU160 before the analyzed data are sent to the central processor 152.

A point load tester (point load tester)164 may be used to determine the subsurface geophysical characteristics of the borehole site. The point load tester 164 preferably utilizes a plurality of cone shaped drill bits at each load point, which themselves are in contact with the ground to test the extent to which a particular subterranean portion can withstand calibrated load levels. The data obtained by the point load tester provides information about the geophysical and mechanical properties of the soil being tested. These data may also be communicated to the GDAU 160.

GDAU160 may also include a Schmidt hammer 166, which is a geophysical instrument that measures rebound stiffness properties of the sample subsurface geology. Other geophysical instruments may also be used to measure the relative energy absorption properties, wear resistance, rock volume, rock quality and other physical properties of the rock mass which together provide a measure of the relative difficulty associated with drilling through a given geological formation. Data obtained from Schmidt hammers are also preferably present in GDAU 160.

In the embodiment shown in fig. 13, a Global Positioning System (GPS)170 is used to provide location data for the GRS 150. According to a U.S. government program for deploying 24 communication satellites in three orbits, known as the Global Positioning System (GPS), various signals transmitted from one or more GPS satellites may be used directly to determine the displacement of the boring tool 24 relative to one or more known reference locations. It is generally understood that the GPS satellite system of the united states government may provide a reserved (or protected) band and a civilian band. Typically, the protected band provides high precision positioning to the precision of being kept secret. However, the protected band is generally used exclusively for military or other government purposes and is modulated in such a way that it is practically useless for civilian applications. Whereas the citizens band is modulated to significantly reduce the obtainable accuracy, typically in the range of one hundred to three hundred feet.

However, combining one or more GPS signals with one or more ground-based reference signal sources allows for indirect use of the civilian GPS band in higher accuracy applications. Positioning accuracy on the order of one centimeter is currently achievable by utilizing various known signal processing techniques, commonly referred to as Differential Global Positioning System (DGPS) signal processing techniques. As shown in fig. 13, the GRS150 uses signals generated by at least one GPS satellite 172 in combination with signals generated by at least two base transponder 174, although in some applications the use of one base transponder 174 may suffice. Various known methods may be employed to utilize the DGPS signals, i.e., using one or more base station transponder 174 and a GPS satellite 172 signal and a rover GPS receiver 176 connected to the control unit 32, to accurately resolve the relative motion of the boring tool 24 with respect to the reference position of the base station transponder 174 using a GPS satellite signal source.

In another embodiment, a land-based positioning system employing range radar system 180 may be utilized. The range radar system 180 preferably includes a plurality of base station radio Frequency (FM) transponders 182 and a mounting system. The range radar system 180 preferably includes a plurality of base station radio Frequency (FM) transponders 182 and a flow transponder 184 mounted on PDU 28. The base station transponder 182 transmits an RF signal that is received by the flow transponder 184. The flow transponder 184 preferably includes a computer that calculates the distance of the flow transponder 184 from each base station transponder 182 and then its position relative to all base station transponders 182 by various known radar techniques. The location data collected by the ranging radar system 180 is transmitted to the GRS150 for storage in the route record database 154 or the route mapping system 158.

In yet another embodiment, an ultrasonic positioning system 190 may be used with the base station transponder 192 and the streaming transponder 194 attached to the PDU 28. The base station transponder 192 transmits a signal having a known time base value that is received by the flow transponder 194. Preferably, the flow transponder 194 includes a computer that calculates the distance of the flow transponder 194 relative to each base station transponder 192 by reference to the clock speed of the source ultrasonic wave. The computer of the flow transponder 194 also calculates the position of the flow transponder 194 relative to all base station transponders 192. It should be understood that various other known land-based or satellite-based positioning systems and techniques may be used to accurately determine the path of the boring tool 24 along the path of the subsurface.

Figure 14 illustrates an underground boring tool 24 for performing a boring operation along an underground path at a boring site. An important advantage of the novel geolocation unit 150 generally depicted in FIG. 14 is the ability to accurately navigate the boring tool 24 along a predetermined borehole path, and to accurately map subsurface borehole paths in a route-mapping database 158 connected to the control unit 32. It may be most desirable to: an initial survey of the planned drilling site is completed before the drilling operation is commenced in order to accurately determine the drilling path, avoiding difficulties (such as previously buried facilities or other obstacles, including rock) as discussed previously.

Actual location data is collected by the geographic recording system 150 and stored in the route fill database 158 as the boring tool 24 progresses along the predetermined boring route. Any intentional deviation from the predetermined route stored in the planned route database 156 is accurately recorded in the route fill database 158. The unintended deviation is preferably corrected to keep the boring tool 24 advanced along the predetermined subterranean path. Once the drilling operation is complete, the data stored in the route fill database 158 may be downloaded to a personal computer (not shown) to construct an "as is" underground map of the drilling site. Then, an accurate map of the facilities or other pipes installed along the borehole route may be constructed from the route mapping data and thereafter may be used as discussed previously with reference to FIG. 14 where it is desired to gain access to or avoid such buried pipes, and accurate mapping of the borehole site may be accomplished using the global positioning system 170, the range radar system 180 or the ultrasonic positioning system 190 as discussed previously with reference to FIG. 13. The mapping system with the GPS system 170 preferably includes first and second base station transponders 200 and 202, and one or more GPS signals 206 and 208 received from GPS satellites 172. A mobile transponder 210 is provided, preferably connected to the control unit 32, for receiving GPS satellite signals 206 and base station transponder signals 212 and 214 (which are transmitted from transponders 200 and 202, respectively) to determine the position of the control unit 32. As discussed previously, a modified form of differential GPS location techniques may be utilized to enhance location accuracy to the centimeter range. A second flow transponder 216 is provided, preferably connected to PDU28, for receiving GPS satellite signals 208 and base station transponder signals 218 and 220 (which are transmitted from base station transponders 200 and 202, respectively) to determine the location of PDU 28.

In another embodiment, land-based ranging radar system 180 includes three base station transponders 200, 202, and 204 and flow transponders 210 and 216 connected to control unit 12 and PDU28, respectively. It should be noted that a third land-based transponder 204 may be provided as a backup transponder for a system using GPS satellite signals 206 and 208 in the event of a temporary interruption in the transmission of GPS satellite signals 206 and 208 due to purposeful or inadvertent occurrence. The location data of the control unit 32 is preferably processed and stored by the GRS150 using the reference signals 212, 214, and 222 received from the ground-based transponders 200, 202, and 204, respectively. The position data for PDU28, obtained using the three reference signals 218, 220 and 224 received from ground-based transponders 200, 202 and 204, respectively, is preferably processed and stored by the local locator 216 associated with PDU28 and then transmitted to the control unit 32 via the data transmission link 34. One embodiment of an ultrasonic positioning system 190 would similarly utilize three base station transponders 200, 202 and 204 and flow transponders 210 and 216 connected to control unit 32 and PDU28, respectively.

Referring now to fig. 15, there is shown in flow chart form the general steps involved in a pre-borehole survey procedure performed to obtain a map of the pre-borehole site and determine the optimal path for the drilling operation prior to performing the drilling operation. Briefly, pre-drilling surveys allow for inspection of the subsurface conditions that a drilling operation will traverse and determination of optimal routes, estimating productivity and estimating the cost of the entire drilling operation.

As shown in fig. 15, a number of land-based transponders are first deployed at appropriate locations around the drilling site (step 300). The control unit 32 and PDU28 are then placed in positions L0 and L1, respectively, at step 302. The geo-recording system 150 is then initialized and calibrated at step 304 to determine the location of the control unit 32 and PDU 28. After successful initialization and calibration, PDU28 is moved along the proposed borehole path, during which PDU data and geographical location data are acquired at steps 306 and 308, respectively. The data collected by PDU28 is preferably analyzed at steps 306 and 308. Data acquisition continues at step 312 until the expected end point of the proposed borehole path is reached, at which point data accumulation ends, as indicated at step 314. The acquired data is downloaded to the control unit 32, which may be a personal computer, at step 316. The control unit 32 then calculates an optimal predetermined path for the drilling operation in order to avoid obstacles and other structures, step 318. If the test at step 320 determines that the predetermined route is satisfactory, the route is loaded into the planned path database 156 at step 322 and the pre-borehole survey process ends at step 324. However, if the test at step 320 determines that the planned route is unsatisfactory because, for example, the survey reveals that the boring tool 24 may strike a rock barrier or have buried facilities, they may be damaged in subsequent boring operations, the PDU28 may be repositioned at the beginning of the survey route at step 326, and the new route surveyed by repeating steps 304 and 318. After a satisfactory course has been established, the pre-borehole survey stops at step 324.

In a first embodiment, the pre-borehole survey process includes collecting geophysical data along a survey route, concurrently with determining position and PDU data collection. This collection activity is illustrated in FIG. 15, which shows the initialization and calibration of the geophysical data acquisition unit 160(GDAU) at step 328, which is done simultaneously with the initialization and calibration of the geographic recording system 150. Simultaneously with the acquisition of PDU28 data and position data, respectively, in steps 306 and 308, geological data is collected by the GDAU160 in step 330. The inclusion of geological data collection provides a more complete characterization of the subsurface media in the proposed borehole path, allowing more accurate productivity and cost estimates for the drilling operation.

In a third embodiment, survey data is compared to previously collected data stored in the routing database 158 to provide an estimate of drilling operation productivity and expense. In this embodiment, after the survey data has been downloaded to the control unit 32 at step 316, historical data is loaded from the route fill database to the control processor 152 at step 332. The data downloaded from the roadmap database 158 includes records of prior exploration and drilling operations, such as GPR and geologic feature measurements and associated productivity data. At step 334, a pre-planned route is calculated in a manner similar to the route calculation indicated at step 318. Birth rate data can be estimated at step 336 for the planned drilling operation by correlating the current subsurface features derived from PDU28 and GDAU160 data with previously made feature measurements and referencing the associated previous productivity results. The productivity data estimated in step 336 can then be used in step 338 to generate a cost estimate for the drilling process. At a subsequent step 320, it is determined whether the pre-planned route is satisfactory. This determination can be made not only by using subsurface features as in the first embodiment, but also by using other criteria, such as estimated duration of the drilling process and estimated cost.

Referring now to fig. 16, there is shown a block diagram of control unit 32 of trenchless subterranean drilling system 12, its various components, and the functional relationship between control unit 32 and various other elements. The control unit 32 includes a central processor 152 that receives input data from the geo-recording system 150, PDU28 and GDAU 160. The central processor 152 calculates the position of the boring tool 24 from the input data. The control processor 152 logs the path taken by the boring tool 24 into the route log database 154 and/or adds it to existing data in the route fill database 158.

In another embodiment, the central processor 152 also receives input data from sensors 230 at the boring tool 24 through a sensor input processor 232. In another embodiment, the central processor 152 loads data corresponding to a predetermined path from the planned route database 156 and compares the measured boring tool position to the planned position. The position of the boring tool 24 is calculated by the central processor 152 based on data provided by the PDU input processor 234, and the PDU input processor 234 receives data received from the PDU 28. In another embodiment, the central processor 152 also utilizes the data provided by the geographic recording system 150 regarding the location of PDU28 to produce a more accurate estimate of the boring tool location.

Corrections to the path of boring tool 24 during a boring operation may be calculated and applied to return boring tool 24 to a predetermined position or path. Central processor 152 controls various aspects of the operation of the boring tool using a trenchless underground boring system control (GBSC) 236. The GBSC236 sends control signals to the borehole control unit that controls the movement of the borehole tool 24. These drilling control units include a rotation control 238 that controls the rotation motor 19 that rotates the drill string 22, a push/pull control 242 that controls the push/pull pump 20 for driving the drill string 22 longitudinally into the borehole, and a directional control 246 that controls a directional excitation mechanism 248 that directs the drilling tool 24 in a desired direction. PDU input processor 234 may also identify an embedded feature, such as a utility, based on data generated by PDU 28. Central processor 152 calculates a path for boring tool 24 that avoids collisions with and subsequent damage to the embedded features.

The general processing and decision steps associated with underground trenchless drilling are shown in fig. 17 and 18. Initially, at step 350, several land-based transponders are placed in appropriate positions around the drilling site, as shown in FIG. 15. The trenchless subterranean drilling system 12 is then placed in an appropriate initial position as indicated at step 352 and the transponder and the georecord system are initialized and calibrated at step 354 and then drilled at step 356. After the borehole has been started, the subsurface is probed by PDU28 at step 358, and then the signature signal is received and analyzed at step 360. At step 362, the GRS receives location data independently of and concurrently with the probing and receiving steps 358 and 360 and determines the location of PDU28 at step 364. After completing steps 362 and 364, the central processor 152 determines the location of the boring tool 24 at step 366. The central processor 152 then compares the measured position of the boring tool 24 to the expected position given in the planned path database 156 at step 368 and calculates whether a correction to the boring tool orientation is required at step 370 and provides a correction if necessary at step 372. At step 374, the trenchless subterranean drilling system 12 continues through the subterranean borehole until the drilling operation is complete as indicated at steps 376 and 378. However, if the boring operation is not complete, the central processor 152 determines whether the PDU28 should be moved to improve the image of the boring tool 24 at step 380. If so, PDU28 is moved at step 382 and probing and GRS data reception steps 358 and 362 are performed. After the boring tool 24 has reached the final destination, operation stops.

In another embodiment, represented by dashed lines in fig. 17 and 18, the central processor 152 records the calculated position of the boring tool 24 in the route fill database 158 and/or the route record database 154 at step 384, after the boring tool position is determined (at step 366). In another embodiment, the steps of comparing the position of the boring tool 24 to the pre-planned position (step 368) and generating any corrections (steps 370 and 372) are omitted, as indicated by the dashed line 386.

Other features may be included on the boring tool 24. In some instances, it may be desirable to make certain measurements, such as the orientation of the boring tool 24, the tangential pressure to the drill string 22, and the temperature of the boring tool 24, in order to more clearly understand the boring operation conditions. Further, as previously described, the measurement of the water pressure at the boring tool 24 may provide an indirect measurement of the depth of the boring tool 24. Figure 19 shows two embodiments with additional boring tool head features. Fig. 19a shows an embodiment that allows the operator to determine the orientation of the boring tool head. When adjusting the direction of the boring tool 24 along the subterranean path, the operator may wish to know the orientation of the boring tool 24 because several known boring tool orientation techniques rely on a preferential orientation of the boring tool. Without knowing the orientation of the boring tool 24, it is not possible to orient the boring tool 24 in an optimal direction according to these known techniques that require knowledge of the orientation of the boring tool 24. It is not possible to simply determine the orientation of the boring tool 24 from the known orientation of the components 23 of the drill string 22 because one or more components 23 of the drill string 22 may twist or slip relative to the other components during the boring operation. Because the drilling operation is occurring underground, it is not surprising that the operator has had a way to detect whether such twisting or slipping has occurred. Therefore, determining the orientation of the boring tool 24 may be important.

FIG. 19a shows an embodiment of a boring tool 400 having a passive time domain signature circuit that includes a single antenna 402 coupled to a terminal 406 by a time delay line 404, as previously discussed with respect to FIG. 5 a. The circuit shown in fig. 19a also includes a mercury switch 408 located at a point along the delay line 404 near the terminal 406. The terminal 406 also includes a dissipative load. When the boring tool 400 is oriented such that the mercury switch 408 is open, a time domain signature is generated by reflecting the incoming probe signal 407 at the open circuit of the mercury switch 408. When the boring tool 400 is oriented such that the mercury switch 408 is closed, a circuit is completed from the antenna 402 to the dissipative load 406 through the delay line 404. The detection signal 407 is not reflected from the dissipative load 406 at this time, so no characteristic signal is generated. The generation of the characteristic signal 409 received by PDU28 is shown in fig. 19b as a function of time. The top trace 407b shows the probing signal 407, denoted Ip, plotted as a function of time. As the boring tool 400 rotates and moves along a subterranean path, the resistance Rm of the mercury switch 408 changes from low to high, as shown by the middle trace 408 b. The regular opening and closing of mercury switch 408 modulates a characteristic signal 409b, denoted as Is, received at the surface. This modulation maintains a constant phase relative to the optimal orientation of the boring tool 24. The lower trace does not represent the delay effect of the time delay line 404 because the time scales differ too much (the delay of the signature signal 409 is on the order of 10 nanoseconds and the time taken for one revolution of the boring tool 24 is typically between 0.1 and 1 second). Detecting such a characteristic signal 409 modulated by PDU28 allows the operator to determine the orientation of the boring tool head. It should be understood that other embodiments of the signature generator described above may also include a mercury switch 408, preferably including a dissipative load 406, to generate the modulated signature signal 409 for the purpose of detecting the orientation of the boring tool 24.

The embodiment shown in fig. 19c allows the sensor to detect the environment of the boring tool 410. An active time domain signature generation circuit is shown that includes a receive antenna 412 coupled to a transmit antenna 414 through active time domain circuitry 416. The sensor 418 is coupled to the active time domain circuit 416 through a sensor load 420. In this embodiment, a sensor 418 is located at the tip of the boring tool 410 to measure the pressure of the water at the boring tool 410. The active time domain circuitry 416 detects the reading from the sensor 418 and converts the reading into a modulated signal, which is then used to modulate the actively generated signature signal 415. This process is described with reference to fig. 19d, which shows several signals as a function of time. The top signal 413d represents the probing signal Ip received by the receiving antenna 412. The second signal 415d represents the actively generated signature signal Ia, which is the signature signal generated assuming that the signature signal is not modulated. The third trace 416d represents the amplitude modulation signal Im generated by the active time domain circuit 416 and the last trace 422d represents the characteristic signal Is after amplitude modulation. Modulated signature 415 is detected by PDU 28. The modulated signal is then determined by signal processor 60 in PDU28 to provide data regarding the output of sensor 418.

The modulation of the characteristic signal is not limited to the time domain signal amplitude modulation combination shown in fig. 19. This combination is provided for illustration only. It should be understood that other embodiments may include amplitude modulation of the frequency domain signature signal and frequency modulation of both the time and frequency domain signature signals. Further, the boring tool 24 may include two or more sensors, rather than only a single sensor as in the embodiments described above.

Figure 20a shows another embodiment of the present invention in which a separate active beacon is used to transmit information to PDU28 regarding the orientation or environment of the boring tool 430. In this embodiment shown in FIG. 20a, the boring tool 430 includes a passive time domain signature circuit that utilizes a single antenna 432, a time delay line 434, and a switch 436 for reflecting electrical signals. A single antenna 432 is used for receiving the probing signal 433 and transmitting the signature/beacon signal 435. The active beacon circuit 438 generates a beacon signal, preferably having a selected frequency in the range of 50KHz to 500KHz, which is mixed with the signature signal generated by the terminal 436 and transmitted by the antenna 432 as a combined signature/beacon signal 435. The mercury switch 440 is located between the active beacon circuit 438 and the antenna 432 so that the mercury switch 440 only acts on the signal from the active beacon circuit 438 and does not act on the signature signal generated by the terminal 436. When the boring tool 430 is oriented such that the mercury switch 440 is open, the beacon signal circuit 438 is disconnected from the antenna 432 and no signal is transmitted from the active beacon circuit 438. When the boring tool 430 is oriented to close the mercury switch 440, the active beacon circuit 438 is connected to the antenna 432, and the signal from the active beacon circuit 438 is transmitted along with the signature signal as signature/beacon signal 435. The effect of the mercury switch on the signature/beacon signal 435 was previously described with respect to fig. 19 b. The top trace 438b represents the signal Ib generated by the active beacon circuit 438 as a function of time. As the boring tool rotates and moves along the subterranean path, the resistance Rm of the mercury switch 440 changes from low to high, as shown by the middle trace 440 b. The continuous opening and closing of the mercury switch 440 produces a modulated continuous signature/beacon signal 435b, denoted Im, which is received at the surface by PDU 28. Only the beacon signal component, and no signature signal component, is represented in signal Im435 b. The modulation of signal Im435b maintains a constant phase relative to the optimal orientation of the boring tool 430. Analysis of the beacon signal modulation by the beacon receiver/analyzer 61 on PDU28 allows the operator to determine the orientation of the boring tool head.

The embodiment shown in FIG. 20c allows several sensors to detect the environment of the boring tool 450, where active beacons are used to transmit sensor data. The active time domain signature generation circuit shown in the figure includes a receive antenna 452, a transmit antenna 454 and an active time domain signature circuit 456, all of which are coupled by a time delay line 457. An active beacon circuit 460 is also connected to the transmit antenna 454. The sensor 458 is coupled to an active beacon circuit 460 by a sensor lead 462. In this embodiment, a sensor 458 is placed near the tip of the boring tool 450 for measuring the water pressure at the boring tool 450. The sensor readings are detected by the active beacon circuit 460 and the signal from the sensor 458 is converted to a modulated signal. This modulated signal is then used to modulate the active beacon signal generated by active beacon circuitry 460. To illustrate in particular the generation of the signature/beacon signal 455 transmitted to PDU28, several signals are shown in fig. 20d as a function of time. Signal 453d represents the probe signal Ip received by the receive antenna 452. The second signal 456d represents the time delayed characteristic signal Is generated by the active time domain circuit 456. A third signal 460d (denoted Ic) represents a combination of the time delay characteristic signal Is456d and the unmodulated signal generated by the active beacon circuit 460. The last trace 455d represents the signal Im received at the surface, which Is a combination of the time delay characteristic signal Is456d and the signal generated by the active beacon circuit 460 (which has been modulated in accordance with the readings of sensor 458). The modulated active beacon signal is detected by beacon signal detector 61 in PDU28 and then analyzed appropriately to provide data to the user regarding the output of sensor 458.

It will, of course, be understood that various modifications and additions can be made to the preferred embodiment discussed hereinbefore without departing from the scope and spirit of the present invention. Thus, the scope of the invention should not be limited by the particular embodiments described above, but should be defined only in accordance with the following claims set forth below and their equivalents.

Claims (32)

1. A system for detecting a position of an underground boring tool, comprising:

generating means separate from the boring tool for generating the detection signal;

generating means for generating a characteristic signal at the boring tool in response to the detection signal; and

and a detecting device for detecting the position of the drilling tool by using the characteristic signal.

2. The system of claim 1, wherein the probe signal is an electromagnetic signal.

3. The system of claim 1, wherein the probe signal is an acoustic signal.

4. The system of claim 1 wherein the means for generating the signature comprises a subsurface permeable radar system.

5. The system of claim 4 wherein the penetrable subsurface radar system produces a three-dimensional image of the subsurface.

6. The system of claim 1, wherein the signature signal is passively generated by its generating means.

7. The system of claim 1, wherein the signature signal is actively generated by the generating means.

8. The system of claim 1, wherein the characteristic signal polarization direction is orthogonal to the polarization direction of the probe signal.

9. The system of claim 1, wherein the signature signal has a signature in either the time domain or the frequency domain.

10. The system of claim 1, including a locating device for determining the geographic location of the boring tool.

11. The system of claim 1, comprising determining means for determining that the boring tool is to follow a predetermined path.

12. The system of claim 1, comprising recording means for recording the subterranean path created by the boring tool.

13. The system of claim 1, comprising:

a feature extraction means for extracting a feature of the subterranean medium through which the boring tool bore passes; and

a storage device for storing characteristics of a subterranean medium.

14. A subterranean drilling system, comprising:

a drilling tool;

a drive means for driving the boring tool, thereby creating a subterranean path;

a generator separate from the boring tool for generating a detection signal;

a signature signal generator for generating a signature signal at the boring tool in response to the detection signal; and

and a position detector for detecting the position of the boring tool along the underground path using the characteristic signal.

15. The system of claim 14, wherein the boring tool includes a direction control device coupled to the drive device for controlling a boring direction of the boring tool.

16. The system of claim 14, including a locating device for determining the geographic location of the boring tool.

17. The system of claim 14, comprising:

the underground characteristic extraction system is used for extracting underground composition characteristics of the underground path; and

a computer coupled to the subsurface feature extraction system for determining the subsurface path to avoid obstruction of the boring tool.

18. The system of claim 14, comprising:

a computer for comparing the underground path generated by the boring tool with a predetermined underground route to generate a comparison signal indicative of a discrepancy between the underground path and the predetermined underground route;

wherein the computer is responsive to the comparison signal to effect a correction to the direction of the borehole by the boring tool.

19. The system of claim 14, comprising:

a subsurface permeable radar system for generating subsurface feature data associated with a predetermined subsurface borehole path; and

a computer for correlating the subsurface feature data with existing drilling operation data to generate estimated drilling operation productivity information.

20. The system of claim 19, wherein the computer uses the estimated drilling operation productivity information to control the drive mechanism.

21. The system of claim 14, wherein the probe generator comprises a subsurface permeable radar system, the subsurface permeable radar system further generating subsurface feature data associated with the subsurface path, the system further comprising:

and a computer connected to the subsurface penetration radar system for storing the subsurface feature data in a database.

22. The system of claim 14, wherein the boring tool comprises a sensor.

23. The system of claim 22, wherein the boring tool further comprises means for transmitting data generated by the sensor.

24. A method of detecting the position of an underground boring tool, comprising the steps of:

generating a probing signal from a signal source separate from the boring tool;

generating a signature signal at the boring tool in response to the probing signal; and

the position of the boring tool is detected using the characteristic signal.

25. The method of claim 24, wherein the step of generating a probe signal comprises the step of generating an electromagnetic probe signal.

26. The method of claim 24, wherein the step of generating a probe signal includes the step of generating an acoustic probe signal.

27. The method of claim 24, wherein the step of generating a probe signal comprises the step of generating a probe signal using a subsurface penetrating radar system.

28. The method of claim 24, wherein the step of generating a signature signal comprises the step of passively generating a signature signal.

29. The method of claim 24, wherein the step of generating a signature signal comprises the step of actively generating a signature signal having a signature in one of a time domain and a frequency domain.

30. The method of claim 24, wherein the step of generating the signature signal comprises the step of generating the signature signal with a polarization direction orthogonal to a polarization direction of the probe signal.

31. The method of claim 24, wherein the step of detecting the position of the boring tool further comprises the step of determining the position of the boring tool in three dimensions using a subsurface penetrating radar system.

32. The method of claim 24, further comprising the step of modifying the production rate of the boring tool based on the position of the boring tool.