HK1243153B - Apparatus and method for multimode steering and homing system - Google Patents

Description

Apparatus and method for a multi-mode steering and homing system

This application is related to and claims priority to and the benefit of U.S. Provisional Patent Application No. 14/864,800, filed September 24, 2015, which is incorporated herein by reference in its entirety.

Technical Field

The present application relates generally to steering tools for horizontal directional drilling and, more particularly, to a system and method for common mode use of steering information and homing information.

Background Art

Drilling tools are well-known, steerable drill bits that may carry sensors, transmitters, and associated electronics. Drilling tools are typically controlled by a drill string that can be extended from a drilling rig. The drill string is typically formed from drill rod segments, hereinafter referred to as drill rods, which can be selectively attached to one another for advancing and retracting the drill string. Steering is typically accomplished using bevels on the drill bit. Advancing the drill string while rotating will cause the drill bit to travel straight forward, while advancing a drill string with bevels oriented at a fixed angle will cause the drill bit to deflect in a certain direction.

To monitor the progress of a drilling tool within a horizontal directional drilling site, one approach currently employed is commonly referred to as a "steering tool." This term is used to describe an overall system that essentially predicts the position of the drilling tool as it advances through the earth using a drill string, allowing the tool to be steered within the earth along a planned drilling path. Steering tool systems are considered distinct from other types of positioning systems used in horizontal directional drilling, at least for the following reason: the position of the drilling tool is monitored in a step-by-step manner as the drilling tool advances through the earth. For each position of the drilling tool, the pitch and yaw angles of the drill bit are measured in conjunction with the extension of the drill string. From this, the position coordinates of the drilling tool are obtained through numerical integration. The nominal or measured drill string length serves as the step size during the integration. Consequently, position errors accumulate as the tool advances through the earth. These position errors can be at least partially attributed to pitch and yaw measurement errors, as well as subsurface perturbations of the Earth's magnetic field, which can result in yaw measurement deviation errors. Consequently, the drilling tool can deviate significantly from the planned endpoint target.

In contrast, the homing system relies on an electromagnetic signal transmitted from the drilling tool. The electromagnetic signal is received at a receiving location for generating a homing command for guiding the drilling tool to a target relative to the receiving location. It will be appreciated that in the homing system, numerical integration of the positioning parameters of the drilling tool is unnecessary, thereby eliminating concerns about cumulative position offset errors. An example of an advanced homing system is provided by U.S. Patent No. 6,727,704, which is commonly owned with the present application and is incorporated herein by reference. However, the applicant recognizes that the range of the electromagnetic signal from the drilling tool to the receiving location can be significantly shorter than the length of the intended drilling path.

Another form of prior art system for monitoring drilling tools uses a device commonly referred to as a walking locator. In this system, an operator carries a walking locator above the surface of the earth to receive electromagnetic signals. The position of the drilling tool can be determined based at least in part on the operator's ability to change the positional relationship between the mobile locator and the drilling tool. In this way, various field-defined points can be identified on the surface of the earth that characterize the electromagnetic signals. Applicants recognize that in some cases, the use of a walking locator is impractical. For example, the drilling path may extend under a busy highway, river, lake, or other such obstructions.

The foregoing examples of the related art and limitations associated therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those skilled in the art after reading this specification and studying the drawings.

Summary of the Invention

The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools, and methods, which are intended to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-mentioned problems have been reduced or eliminated, while other embodiments involve other improvements.

Generally speaking, a system includes a boring tool movable by a drill string having an extendable length, the drill string being guided to the boring tool from a drill rig for performing a horizontal directional drilling operation that advances the boring tool through the earth. In one aspect of the present disclosure, an apparatus and associated method are described for use in conjunction with a system that includes a transmitter supported by the boring tool for transmitting an electromagnetic homing signal. The transmitter includes a magnetometer for generating a magnetic reading representative of the Earth's magnetic field and an accelerometer for generating a pitch reading representative of the pitch orientation of the boring tool. A portable device is configured to monitor the electromagnetic homing signal in a homing mode and to receive the electromagnetic homing signal for use in generating a homing command to guide the boring tool to a target position relative to the portable device. The processor is configured to generate steering commands to guide the drilling tool in a steering mode based on a drilling plan using magnetic readings, pitch readings, and an extendable length of the drill string so as to introduce at least some position error between the actual position of the underground tool and the predicted position of the underground tool, and to switch from the steering mode to the homing mode based at least in part on monitoring the electromagnetic homing signal when the drilling tool approaches the portable device and thereafter moves the drilling tool to a target position to compensate for the position error.

In another aspect of the present disclosure, an apparatus and associated method are described for use in conjunction with a system comprising a transmitter supported by a drilling tool for transmitting an electromagnetic homing signal. The transmitter comprises a magnetometer for generating magnetic readings representative of the Earth's magnetic field and an accelerometer for generating pitch readings representative of the pitch direction of the drilling tool. A portable device comprises an antenna configured to receive the electromagnetic homing signal to generate electromagnetic information when the portable device is within a reception range of the transmitter. A processing device is configured to generate steering commands to guide the drilling tool in a steering mode based on a drilling plan using the magnetic readings, the pitch readings, and the extendable length of the drill string so as to introduce at least some position error between the actual position of the underground tool and the predicted position of the underground tool, and to guide the drilling tool in a homing mode to a target position relative to the portable device to compensate for the position error when the portable device is within the reception range.

In another aspect of the present disclosure, an apparatus and associated method are described for use in conjunction with a system comprising a transmitter supported by a drilling tool for transmitting an electromagnetic homing signal. The transmitter comprises a magnetometer for generating magnetic readings representative of the Earth's magnetic field and an accelerometer for generating pitch readings representative of the pitch direction of the drilling tool. A portable device comprises an antenna configured to receive the electromagnetic homing signal to generate electromagnetic information when the portable device is within a reception range of the transmitter. A processing device is configured to generate steering commands to guide the drilling tool in a steering mode based on a drilling plan using the magnetic readings, the pitch readings, and the extendable length of the drill string so as to introduce at least some position error between the actual position of the underground tool and the predicted position of the underground tool, and to guide the drilling tool in a homing mode at least approximately back to the drilling plan to compensate for the position error when the portable device is within the reception range.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in the referenced figures of the accompanying drawings.The embodiments and figures disclosed herein are intended to be illustrative rather than restrictive.

1 is a schematic elevation view of a system utilizing an embodiment of a multi-mode steering and homing system according to the present disclosure.

FIG. 2 illustrates a block diagram of an embodiment of an electronics package that may be carried by a drilling tool.

3 is a block diagram of components that may comprise an embodiment of an above-ground transceiver device that may be located at a drilling rig.

4 and 5 are schematic diagrams of a drilling plan in elevation and plan view, respectively, where the starting position and the target position are shown together with additional parameters.

6 is a schematic diagram of an embodiment of the appearance of a display for presenting steering mode and homing mode guidance to an operator.

7a is a schematic diagram in plan view illustrating a sample drilling plan associated with an actual drilling path, wherein an initial portion of the actual drilling path is performed in a steering mode and a final portion of the actual drilling path ends in a homing mode to reach a target location.

7b is a schematic plan view of an underground operation showing the drilling tool relative to the portable device positioned on the drilling plan.

7c is a schematic elevational view showing the drilling tool relative to a target, shown here to facilitate discussion of identifying the position of the drilling tool relative to the portable device.

FIG. 7 d is a graphical illustration of additional orientation parameters that complement FIG. 7 c .

7e is a schematic plan view of a drilling operation showing intermediate targets that may be defined along a drilling plan such that the system enters a homing mode to return the drilling tool to the drilling plan at each intermediate target to eliminate errors that may have accumulated in the steering mode.

Figure 7f is a schematic diagram, which may be a plan view or an elevation view, showing the return of the drilling tool to the drilling plan.

FIG8 illustrates a flow chart of an embodiment of a method for operation of the system of the present disclosure.

9-11 each illustrate a hypothetical drilling plan that was numerically simulated as a validation of the disclosed method.

FIG. 12 is an example of a single simulation run for the straight borehole plan of FIG. 9 in the form of an error map.

DETAILED DESCRIPTION

The following description is provided to enable one of ordinary skill in the art to make and use the invention, and is provided in the context of a patent application and its requirements. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles taught herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments shown, but is to be given the widest scope consistent with the principles and features described herein, including modifications and equivalents as defined within the scope of the appended claims. Note that the drawings are not to scale and are pictorial in nature in a manner believed to best illustrate the features of interest. Descriptive terminology may be used for these descriptions, however, this terminology has been adopted to facilitate the reader's understanding and is not intended to be limiting.

This application discloses a system, associated apparatus, and method that combine the convenience and functionality of a steering tool with the convenience and functionality of a homing system. Applicants recognized that while the exit location of a drilling section is often readily accessible, this is not always the case for the entire length of the drilling section, such as when drilling beneath a river. Therefore, drilling beneath obstructions—where conventional positioning is impossible—can be performed in steering mode. Thereafter, the drilling section can be completed in homing mode, which complements steering mode by providing compensation for accumulated position errors. During steering and homing modes, drilling can proceed without requiring a technician to operate a walkie locator, which continuously positions the drilling tool, to provide steering information to the drill rig operator, regardless of whether drilling beneath, over, and/or around obstacles is required. In other words, the present disclosure always provides guidance information directly to the drill rig operator. Consequently, the chance of misinterpretation of the walkie locator's indicators by the walkie locator operator and miscommunication between the walkie locator operator and the drill rig operator are eliminated. The guidance information provided to the drill rig operator can be the same regardless of whether the system is operating in steering or homing mode. During steering and homing modes, communication of sensor data and commands between the drilling tool and the drill rig may be facilitated by using the drill string as an electrical conductor, thereby conveniently streamlining system operation compared to conventional systems, including wire-in-pipe systems.

Turning now to the drawings, wherein like components are designated by like reference numerals throughout the various figures, attention is immediately drawn to FIG1 , which is a front elevational view schematically illustrating an embodiment of a horizontal directional drilling system, generally designated by reference numeral 10, and made in accordance with the present disclosure. While the illustrated system illustrates the present invention within the framework of a horizontal directional drilling system and its components for performing subterranean boring operations, the present invention may be adapted by one of ordinary skill in the art for other suitable uses while still applying the teachings disclosed herein.

FIG1 shows a system 10 operating in an area 12 where an obstruction, such as a river 13, is present. System 10 includes a drilling rig 14 having a drill string 16 extending therefrom to a drilling tool. The drilling tool is shown in a first position, indicated by reference numeral 20, operating in a steering mode, and in a second position, indicated by reference numeral 20′, in dashed lines, operating in a homing mode. The drill string can be pushed into the earth to move the drilling tool 20 at least generally in a forward direction 22 indicated by an arrow. System 10 can be configured to guide the drilling tool based on a drilling plan 24 (two portions of which are shown using dashed lines) that can terminate at a target location T _BP . As will be described further, steering commands can be generated to guide the drilling tool along the drilling plan 24. The drilling plan is typically predetermined prior to the actual horizontal directional drilling operation. The drilling plan can be customized to accommodate any set of circumstances, for example, to avoid pre-existing utilities, structures, obstructions, and/or property boundaries. The drilling plan can be established in any suitable manner. For example, an increased depth may be necessary based on an obstruction such as a river 13. The drill plan may also consider entry angles, such as those shown in FIG1 , and exit angles for entering the mine or exiting the surface based on the location of the target _TBP . In the plan view of area 12, the drill plan may be steered around obstructions such as boulders or structures. Other factors may influence the development of the drill plan, including the physical limitations of the drilling equipment. These limitations include, but are not limited to, the tightest/smallest bend radius of the drill pipe segments being used.

Continuing with reference to FIG1 , the drill string 16 is partially shown and is segmented, consisting of a plurality of removably attached individual drill pipe segments, two of which are designated 1 and N, having segment or section lengths and wall thicknesses. The drill pipe segments are interchangeably referred to as drill pipe having a rod length. During operation of the drilling rig, one drill pipe segment at a time can be added to the drill string and pushed into the ground by the drilling rig using a movable carriage 25 to advance an underground tool. The drilling rig 14 may include a suitable monitoring device 26 for measuring the movement of the drill string in the ground, such as the monitoring device described in U.S. Patent No. 6,035,951, entitled “SYSTEMS, ARRANGEMENTS AND ASSOCIATED METHODS FOR TRACKING AND/OR GUIDING AN UNDERGROUND BORING TOOL” (hereinafter referred to as the '951 patent), which is commonly owned with the present application and incorporated herein by reference. The monitoring device 26 is also shown in the further enlarged inset 27 within the dashed circle. For example, the motion device can transmit ultrasonic energy 28 from the transmitter to the receiver to track the movement of the carriage, and this information can be used in conjunction with the state of the drill string clamp 30 to determine which movements of the carriage are used to advance the drilling tool. For example, when the drill string clamp 30 is unclamped, movement of the carriage in direction 22 is used to extend the drill string.

Each drill pipe segment defines a through-bore 35 (one of which is indicated) extending between opposite ends of the segment. The drill pipe segments may be fitted with what are commonly referred to as casing and pin fittings, such that each end of a given drill pipe segment may be threadedly engaged with the adjacent end of another drill pipe segment of the drill string in a well-known manner. After the drill pipe segments are joined to form the drill string, the through-bores of adjacent drill pipe segments align to form an overall path 36, indicated by arrows. Path 36 may provide a pressurized flow of drilling fluid or mud in the direction of the arrow from the drilling equipment to the drill bit, as will be described further.

The location of the boring tool within the area 12 and the subsurface path followed by the boring tool may be established and displayed at the drilling rig 14, for example, on a console 42 using a display 44. The console may include a processing device 46 and a control actuator device 47. In some embodiments, the control and monitoring of operating parameters may be automated.

The drilling tool 20 may include a drill bit 50 with an inclined surface for use in steering based on roll orientation. In other words, when pushed forward without rotating, the drill bit will generally deflect based on the roll orientation of its inclined surface. On the other hand, as indicated by the double-headed arrow 51, the drill bit is typically caused to travel in a straight line by rotating the drill string as it is pushed. Of course, predictable steering presupposes appropriate soil conditions. It should be noted that the aforementioned drilling fluid may be delivered under high pressure as a jet 52 to cut through the earth ahead of the drill bit, thereby carrying drill cuttings to the surface and serving to cool and lubricate the drill bit. The drilling tool 20 includes an underground housing 54 that houses an electronics assembly 56. The underground housing is configured to allow the drilling fluid to flow to the drill bit 50 around the electronics assembly. For example, the electronics assembly may include a cylindrical housing configuration centrally supported within the housing 54. The drill bit 50 may include a box fitting that receives a pin fitting of the underground housing 54. Opposite ends of the underground housing may include a box assembly that receives the pin assembly of an isolator 60, with the isolator 60 forming an electrically isolated gap or break between its opposite ends. The other end of the isolator 60 may include a box assembly that receives the pin assembly from the drill pipe 1. The underground electronics assembly 56 may include a drill string transceiver 64 and a homing transceiver 65. Further details regarding the drill string transceiver will be provided at appropriate locations below. In some embodiments, the homing transceiver 65 may transmit an earth-penetrating signal 66, such as a dipole positioning signal, and may receive electromagnetic signals generated by other components, as will be described at appropriate locations below. This example assumes that the electromagnetic signal 66 is a homing signal in the form of a dipole signal for descriptive purposes. Therefore, the electromagnetic signal 66 may be referred to as a homing signal. It should be understood that the homing signal can be modulated like any other electromagnetic signal, and the modulated data can be subsequently recovered from the signal. The functionality of the signal used to generate the homing command to be described depends on the characteristic shape of the flux field and its signal strength, rather than its ability to carry modulation. Therefore, modulation is not required. Information about certain parameters of the drilling tool, such as pitch and roll (orientational parameters), temperature, drilling fluid pressure, and annular pressure around the drilling tool, can be measured by a suitable sensor assembly 68 located within the drilling tool, including, for example, a pitch sensor, a roll sensor, a temperature sensor, an AC field sensor for sensing the proximity of a 50/60 Hz utility line, and any other desired sensors, such as a DC magnetic field sensor for sensing yaw orientation (a three-axis magnetometer with a three-axis accelerometer to form an electronic compass for measuring yaw orientation) and one or more pressure sensors. Note that pitch and roll orientation can be derived based on the output of the three-axis accelerometer. Any suitable combination of this information can be modulated onto a signal 66 and/or transmitted to the drill rig via an isolator 60, using the drill string as an electrical conductor. The drill string transceiver 64 can include a processor that interfaces with the sensor assembly 68 and the homing transceiver 65 as needed. A battery (not shown) can be provided within the housing for power.

Portable device 80 is shown positioned on the surface of the Earth and in a further enlarged inset view 81 within the dashed circle. Note that the wiring between components within device 80 has been only partially shown to maintain clarity of illustration, but it should be understood that it exists and can be easily implemented by one of ordinary skill in the art based on the overall disclosure. The portable device can be used to detect electromagnetic signal 66. One embodiment of a suitable and highly advanced portable receiver is described in the above-incorporated U.S. Patent No. 6,727,704. The portable device includes a triaxial antenna cluster 82 that measures three orthogonally arranged components of electromagnetic flux, designated as _bx , _by, and _bz , in response to electromagnetic signal 66. One useful antenna cluster contemplated for use herein is disclosed in U.S. Patent No. 6,005,532, which is commonly owned with the present application and incorporated herein by reference. Antenna cluster 82 is electrically connected to an electronics assembly 84. The electronics assembly may include, for example, one or more processors, any suitable type of memory, and an analog-to-digital converter. As is known in the art, the latter should be capable of detecting frequencies at least twice the highest frequency of interest. A tilt sensor device 86 may be provided to measure the gravity angle, which can be used to determine the components of flux in a horizontal coordinate system. In one embodiment, the tilt sensor device may include a three-axis accelerometer. The device 80 may also include a graphical display 90. It should be understood that the graphical display 90 may be a touch screen to facilitate operator selection of various buttons defined on the screen and/or to facilitate scrolling through the screen for operator selection. The touch screen may be used alone or in combination with an input device 93, such as a trigger for selecting functions. The input device may be used without requiring a touch screen. In addition, numerous variations of the input device may be employed, including scroll wheels and other suitable known selection devices. Any parameters considered related to drilling (e.g., pitch) may be displayed on the display 44 and/or on the display 90 retrieved from the drilling tool. The device 80 may use an antenna 95 to transmit and/or receive telemetry signals 94, while the drill rig 14 may use an antenna 97 to transmit and/or receive telemetry signals 96. These telemetry components may provide for two-way signaling between the drill rig and the device 80, although this is not required. In one embodiment, an antenna 98 may be provided in the device 80 for transmitting a signal 99 to the drilling tool to facilitate communication of information generated by the device 80, as will be further described. Other components (not shown) may be added to the device 80 as desired, such as a magnetometer to assist in determining position relative to the drilling direction and an ultrasonic transducer to measure the height of the device above the ground.

Attention is now directed to the details regarding the underground isolator 60 in FIG1 . Generally, the isolator forms an electrically isolated gap 200 such that a drill string transceiver is electrically coupled across the gap to utilize the drill string as an electrical conductor for bidirectional communication with the drill rig. Advanced embodiments for providing an electrically isolated gap are disclosed in U.S. Published Patent Application Nos. 2014-0055278 and 2014-0262513 , each of which is commonly owned with the present application and each of which is incorporated herein by reference. In another embodiment, utilizing the drill string as an electrical conductor can be facilitated by using a current transformer as described, for example, in U.S. Patent No. 8,695,727 and U.S. Published Patent Application No. 2012-0218863 , each of which is commonly owned with the present application and each of which is incorporated herein by reference.

FIG2 is a block diagram illustrating an embodiment of electronics assembly 56 in greater detail. Assembly 56 may include a subsurface digital signal processor 310, which facilitates all functions of drill string transceiver 64 and homing transceiver 65 in FIG1 . A sensor section 68 may be electrically connected to digital signal processor 310 via an analog-to-digital converter (ADC) 312. Any suitable combination of sensors may be provided for a given application, such as, for example, an accelerometer 320, a magnetometer 322, a temperature sensor 324, and a pressure sensor 326, which may sense the pressure of the drilling fluid before it is ejected from the drill string and/or the pressure within the annular region surrounding the downhole portion of the drill string. An adapter/isolator 60 is schematically shown separating an uphole portion 330 of the drill string from a downhole portion 334 of the drill string for use in one or both of a transmit mode, in which data is coupled to the drill string, and a receive mode, in which data is retrieved from the drill string. As shown, the electronic components are connected across the electrically insulating/isolating gap 200 formed by the isolator using first and second leads 328a, 328b, which may be collectively referred to by reference numeral 328. In embodiments using current transformers, these leads may be connected to the current transformer leads. For transmit mode, an antenna driver section 330 is used, electrically connected between the underground digital signal processor 310 and leads 328, to drive the drill string. In one embodiment, data coupled into the drill string may be modulated using a frequency different from any frequency used to drive the dipole antenna 340, which transmits the aforementioned signal 66 (FIG. 1), to avoid interference, although this is not required. When the antenna driver 330 is off, an on/off switch (SW) 350 selectively connects leads 328 to a bandpass filter (BPF) 352, which has a passband that includes the frequencies of the data signal received from the drill string. BPF 352 is in turn connected to an analog-to-digital converter (ADC) 354, which is itself connected to digital signal processing section 310. Recovery of the modulated data in the digital signal processing section can be readily configured by one of ordinary skill in the art taking into account the particular form of modulation employed.

Still referring to FIG. 2 , dipole antenna 340 can be connected for use in either or both a transmit mode, in which signal 66 is transmitted into the surrounding soil, and a receive mode, in which electromagnetic signals (e.g., signal 99) from FIG. 1 are received. For the transmit mode, an antenna driver section 360 is used, electrically connected between the underground digital signal processor 310 and dipole antenna 340, to drive the antenna. When antenna driver 360 is off, an on/off switch (SW) 370 selectively connects dipole antenna 340 to a bandpass filter (BPF) 372 having a passband that includes the frequencies of data signals received from the dipole antenna. BPF 372 is in turn connected to an analog-to-digital converter (ADC) 374, which is itself connected to digital signal processing section 310. Those skilled in the art can readily configure the transceiver electronics for the digital signal processing section in many suitable embodiments, taking into account the specific modulation format or formats employed and the overall disclosure herein. The design shown in FIG. 2 may be modified in any suitable manner in view of the teachings disclosed herein.

Referring to FIG. 1 and FIG. 3 , the latter is a block diagram of components that may constitute an embodiment of an above-ground transceiver device (generally designated by reference numeral 400) that is connected to the drill string 16 at a drilling rig. An above-ground current transformer 402, located, for example, on the drilling rig 14, is used to couple signals to and/or recover signals from the drill string 16. Current transformer 402 may also be replaced by two electrical leads, one connected to the drill string and one connected to ground. Current transformer 402 may be electrically connected for use in one or both of a transmit mode, in which data is modulated onto the drill string, and a receive mode, in which modulated data is recovered from the drill string. Transceiver electronics 406 are connected to the current transformer and may be powered by a battery or by the drilling rig, providing essentially unlimited power. For the transmit mode, an antenna driver section 410 is used, electrically connected between an above-ground digital signal processor 418 and current transformer 402, to drive the current transformer. Furthermore, in one embodiment, the data coupled into the drill string can be modulated using a frequency different from the frequency used to drive the dipole antenna 340 ( FIG. 6 ) to avoid interference and different from the frequency at which the isolator 60 drives the signal into the underground end of the drill string, although this is not required. When the antenna driver 410 is off, an on/off switch (SW) 420 can selectively connect the current transformer 402 to a bandpass filter (BPF) 422 having a passband that includes the frequencies of the data signal received from the drill string. The BPF 422 is in turn connected to an analog-to-digital converter (ADC) 430, which is itself connected to a digital signal processing section 418. It should be understood that the digital signal processing section 418 and associated components, including the uphole transceiver, can form part of the drilling rig's processing equipment 46 (shown using dashed lines) or can be connected to the drilling rig via a suitable interface 434. The transceiver 406 may send commands to the drilling tool for various purposes, such as controlling transmit power, selecting a carrier frequency, changing the data format (e.g., reducing the baud rate to increase the decoding range), etc. One of ordinary skill in the art may readily configure the transceiver electronics for the aboveground transceiver arrangement in many suitable embodiments, taking into account the particular modulation format or formats employed and in view of this overall disclosure.

Referring to FIG. 4 and FIG. 5 , the former is a schematic elevation view of a drilling plan 500 in the XZ (vertical) plane, extending from a starting position to a target position T _BP , which is the endpoint of the drilling plan, thereby illustrating the depth along _the intended path, while the latter is a schematic plan view of the drilling plan 500 in the XY (horizontal) plane, thereby illustrating the lateral (i.e., left/right) nature of the intended path. For the purposes of this example, it is assumed that the portable device 80 is physically positioned and arranged so that the target position T coincides with the target position T _BP at the end of the drilling plan, although this is not a requirement. In this regard, the target position T may be offset vertically and/or horizontally from T _BP . In the steering mode, a steering command is generated to guide the drilling tool to the target position T _BP . Conversely, in the homing mode, a homing command is generated based on the electromagnetic signal 66 to cause the drilling tool to approach or return to the target position T. Obstacles may exist along at least the initial portion of the drilling plan, but are not shown for clarity of illustration. Note that for clarity of explanation, Figures 4 and 5 are shown in vertical alignment. Although this description is designed with the use of a drilling plan in mind, it should be understood that system 10 can operate with or without a predefined/predetermined drilling plan. Referring to Figures 4 and 5, it should be clear that the drilling plan is not limited to the XZ plane and that drilling along a curved path can be performed. If there is no predetermined drilling plan, the operator can provide a desired drilling depth, and the system can determine the drilling path substantially in real time, including, for example, an entry curve, a main drilling path at the desired drilling depth, and an exit curve. The origin of the XYZ coordinate system can be located on the ground 508 above the center of the transmitter and can be defined as ( _X0 , _Y0 , _Z0 ). Before starting, the operator can place the portable device 80 on the ground ahead of the transmitter relative to the target location T, with the bx _- axis of the antenna 82 (Figure 1) pointing at least generally in the drilling direction. In one embodiment of the initial drilling setup, the Z coordinate axis can extend vertically through the center of the transmitter 20 at the starting position. The transmitter's elongated axis, about which the transmitter rotates, represents the transmitter's yaw orientation, constrained by pitch, and can be used to determine the horizontal X-axis at the surface. In other words, the transmitter's elongated axis and the X-axis are at least coplanar in the plan view of FIG. 5 . The Y-axis is orthogonal to both the X-axis and the Y-axis. The transmitter's depth at the starting position, which can be directly measured, is designated D ₁ ( FIG. 4 ), where the drilling operation begins. Note that D ₁ can be zero, such that the transmitter starting position is at the surface. Therefore, the transmitter's initial position becomes:

(X ₁ , Y ₁ , Z ₁ )=(0, 0, -D1) (1).

The target position T is defined relative to the position of the portable device. T can be the position of the portable device itself, or a position offset downward and laterally relative to the portable device, or a combination of depth and lateral offset. In the former case, if the center of the portable device's triaxial antenna 80 ( FIG. 1 ) is selected as the target T, the target position T can be identified as (X _T , Y _T , Z _T ). In the latter case, if the target position is offset to a depth _DT directly below the device 80, as shown in the figure, the offset target position T can be specified as (X′ _T , Y′ _T , Z′ _T ), such that:

(X′ _T , Y′ _T , Z′ _T )=(X _D , Y _D , (Z _D -D _T )) (2)

Where the subscript D represents a parameter associated with the portable device, and the value _DT represents the depth of the target, including the distance _ZD of the portable device above the ground. Alternatively, if the target location is laterally offset relative to device 80, the target location can be specified as _TOS with coordinates ( _XOS , _YOS , _ZOS ). During drilling, the pitch orientation (i.e., the angle between the horizontal XY plane and the Z axis) can be measured based on accelerometer readings, and the yaw orientation of the transmitter (the angle in the horizontal plane, typically relative to the X axis) is measured by magnetometer 322 (Figure 2). Magnetometer readings relative to magnetic north can be easily converted to a reference to the X axis. In addition, portable device 80 can use antenna 82 to measure the electromagnetic flux from signal 66 as long as the transmitter is within range of the portable device. For the purposes of this example, assume that the total length _XD of the drill plan is 200 feet, and portable device 20 can receive signal 66 as long as the transmitter is within 40 feet of the portable device. When the transmitter 20 is too far from the locator to receive sufficiently accurate flux measurements from the signal 66, the system 10 operates in a steering mode using the pitch and yaw readings in conjunction with the drill string extension/length to determine an estimated drilling path. As a non-limiting example, the drill string length is used in this embodiment as the drilling increment between the pitch and yaw measured positions. However, any suitable increment may be used between the measured positions, such as those measured by the drill string monitoring device 26 of FIG. 1 . Thus, when the uphole end of the Nth drill string is pushed into the earth, the estimated transmitter position is:

where _LR is the average rod length, φ is the pitch orientation of the launcher, and β is the yaw orientation of the launcher.

Attention is now directed to FIG. 6 , which is a screenshot generally designated by reference numeral 600 and diagrammatically illustrates an embodiment of the appearance of display 44 and/or display 90 ( FIG. 1 ) for providing steering guidance to an operator. Guidance parameters Δ(X, Y) on the horizontal axis and ΔZ on the vertical axis may be determined to indicate which direction to turn. The steering guidance may be determined based on how far the estimated transmitter position is from the drilling plan, as determined by equations 3a-3c, and the display of this guidance as shown in FIG. As an example, for a given length of drill string corresponding to a given X coordinate value for the transmitter's position, the X, Y, and Z positions on the drilling plan may be determined and compared to the positions determined based on equations 3a-3c. In the figure, crosshairs 604 represent the desired direction of the drilling tool at its current position relative to the intended drilling path, while steering indicator 610 represents the difference between the actual and desired directions of the drilling tool. Triangle 614 indicates the current roll position of the drilling tool, while ball 618 indicates the position of the drilling tool relative to the drilling plan. The distance of the ball from the center of the crosshairs 604 indicates how far the current direction of the drilling tool is from the desired direction, which is based on the desired path back to the drilling plan from the current position. For example, if the ball 618 is in the upper right quadrant, as shown, the steering should be downward and to the left. This can be achieved by pushing the drill string to advance the drilling tool, with the triangle 614 pointing to the center of the crosshairs 604. As an example, the current pitch and yaw are φ _current and β _current , respectively, and the desired pitch and yaw to return to the planned drilling path are φ _desired and β _desired , respectively. The desired direction can be determined in a suitable manner, such as by turning at the minimum bend radius of the pipe or by reaching the planned drilling path at a given distance from the current position. Therefore, achieving the desired direction requires changes in yaw and pitch by Δβ = β _desired - β _current and Δφ = φ _desired - φ _current , respectively. In this case, the position of the ball 618 relative to the center of the crosshairs is given by:

Δ(X, Y)=Δβ/Δθ _max (4a)

ΔZ = Δφ/Δθ _max (4b).

Where Δθ _max =Lrod/R _min (4c)

In equation (4a), Δ(X,Y) is the horizontal steering command. In equation (4b), ΔZ is the vertical steering command. In equation (4c), L _rod is the rod length and R _min is the minimum bend radius of the drill rod.

Returning to the discussion of equations (3a-3c), these equations are discrete equivalent product dispersions, such that errors in pitch and yaw measurements result in cumulative position errors. Since there is no measurement of true or actual position when operating strictly in steering mode, no correction can be made to account for the cumulative position errors. However, when the transmitter is within range of portable device 80, the latter defines an absolute position, allowing the system to switch to homing mode to guide the transmitter to a target position, regardless of whether the target position is the center of antenna 82 or offset therefrom, as will be described immediately below.

Referring to FIG. 7 a , an area 700 is shown in plan view within the XY plane, including an example of a predetermined drilling plan 704, shown as a dashed line. The drilling plan may lead to a target location T _BP , _which is the endpoint or end point of the drilling plan. A solid line is used to indicate the actual path 710 taken by the drilling tool. It should be understood that deviations of the actual path 710 from the drilling plan 704 may indicate accumulated positional errors, causing the actual path to deviate to either side of the drilling plan. As a non-limiting example, assuming that the target location T is directly below the portable device 80 and coincides with the endpoint T _BP of the drilling plan, the dashed circle 714 represents the range within which the portable device would receive the electromagnetic signal 66 ( FIG. 1 ) as the drilling tool approaches along the actual drilling path. Although a circular reception area corresponding to a three-dimensional spherical area is shown in the plan view of the accompanying drawings, those skilled in the art will appreciate that the shape of the area may vary based on, for example, the local geography surrounding the target. Note that the accumulated error at point 720 on the actual drilling path is represented as a distance offset from point 724 on the drilling plan. In one embodiment, the system may switch from steering mode to homing mode at point 720. From point 720 onward, the actual path then converges to a target position T defined relative to the physical position of the portable device 80. In FIG. 7 a , it is assumed that the target position T _BP at the end point of the drilling plan coincides with the homing target position T defined relative to the portable device, however, this is not required. It should be understood that the system may compensate for offsets of the target position T _BP relative to the homing target position T defined by the portable device. In other words, once the drilling tool is within the reception range shown by circle 714 and the system is operating in homing mode, the drilling path may end based solely on the physical position of the portable device. For example, if the orientation of the portable device relative to the drilling plan is known, then the homing target T′ may be offset from the target position T _BP anywhere within the reception range 714 shown as a circle, as will be discussed further below.

Referring to FIG7b , a portable device 80 and a drilling tool 20 are shown in a schematic plan view during underground operation to illustrate determining the position of the drilling tool relative to the portable device and, therefore, relative to the drilling plan. Assume that the portable device 80 is at position (0, 0, 0) and aligned with the drilling plan 704, with a yaw β _PD relative to the X-axis 750 of a suitable coordinate system (shown in dashed lines). The drilling tool is at position (x, y, z) relative to the portable device, with a yaw of β _{x mtr} relative to the X-axis 750. The magnetic field components measured by the locator along its three orthogonal axes are (b _x , _by , b _z ), as shown in FIG1 . Assuming the angular orientations of the portable device and the drilling tool are known, the position (x, y, z) of the drilling tool can be determined relative to the portable device. To this end, the electromagnetic flux components of the electromagnetic homing signal 66 undergo two rotational transformations to create the orthogonal electromagnetic flux components that the portable device 80 would see if it were in the same angular orientation as the drilling tool. The first rotation is a yaw rotation to rotate the flux component to the flux component that would be received if the yaw axis of the portable device were at the same yaw angle _βxmtr as the drilling tool and its associated transmitter. Therefore, the flux component is first rotated about the Z axis of the coordinate system (i.e., extending outward perpendicular to the plane of the drawing) corresponding to the difference between _βPD and _βxmtr . To this end, a rotation matrix R(ax,ang) is defined, which generates a rotation by an angle "ang" about the axis "ax". After this first transformation, the transformed or projected magnetic field component measured by the portable device is given by:

(b′ _x , b′ _y , b′ _z )=R(Z, β _PD −β _xmtr )*(b _x , by _y , b _z ) (5).

Following the rotation in Equation 5, a second rotation about the X-axis rotates the flux component by an angle δ until the magnetic field component seen by the portable device's Y antenna is equal to zero, as given by:

(b″ _x , 0, b″ _z )=R(X, δ)*(b′ _x , b′ _y , b′ _z ) (6a)

δ=tan-1(b′ _z /b′ _y ) (6b)

where b″ _x and b″ _z are the transformed or projected flux components that have undergone a second rotation.

7c, a front view shows the drilling tool 20 relative to the portable device 80. After performing two rotational transformations, the rotated flux intensity components b" _x and b" _z can be used to determine the horizontal distance S between the portable device and the drilling tool and the depth D of the drilling tool.

Use equations (7a-7f) to determine the transmitter depth D and the horizontal distance S from the portable device's antenna to the transmitter as follows:

D＝r sin(α+φ) (7a)

S＝rcos(α+φ)(7b)

Equations (7a-7f) are based on the known magnetic dipole equations, where and are defined by Equations 7c and 7d. FIG7d shows the variables φ, α, and r relative to the global coordinate system x and z axes and the center of the antenna 82.

With the values of S and D at hand, the position coordinates (x, y, z) of the drilling tool in the coordinate system shown in _FIG7b are then determined by counter-rotating δ about the X axis and β about the Z axis, which is given by:

(x,y,z)=R(Z, _βxmtr )*R(X,-δ)*(-S,O,D) (8)

Where "S" is the horizontal distance between the portable device and the drilling tool, and D is the depth of the drilling tool. Applicants have recognized that the position of the drilling tool can be determined even after the drilling tool has passed from the first approach side 752 of the portable device to, for example, the second exit side 754 of the drilling plan, as will be described below with respect to intermediate target positions. Note that moving the drilling tool from the approach side to the exit side is equivalent to rotating the portable device 180 degrees about the Z axis, i.e., the magnetic field measured by the locator can be transformed so that ( _b'x , _b'y , _b'z ) → ( _-b'x , _-b'y , _b'z ). Based on the foregoing, the relative position of the drilling tool relative to the portable device is determined using the orientation of the portable device relative to the drilling plan and the orientation of the drilling tool relative to the drilling plan, thereby guiding the drilling tool to any position within the reception range of the portable device. For the purposes of this disclosure, the homing mode is considered to include guiding the drilling tool to any target position based on the electromagnetic signal 66 - as long as the portable device, which deviates from the target position, is still within the reception range of the drilling tool.

In the homing mode and with reference to FIG7 c , as described above, with respect to providing a homing target for the drilling tool 60, the device 80 can be selectively configured in two different ways. Two homing configurations are described, for example, in U.S. Patent No. 6,250,402 (hereinafter referred to as the '402 patent), which is jointly owned with the present application and incorporated herein by reference, so that left/right and up/down homing commands can be generated to guide the drilling tool to the device or to an offset target. In addition, this arrangement determines the depth D of the drilling tool and the horizontal distance S from the drilling tool to the target similarly to the above-mentioned Formulas 7a and 7b. U.S. Patent No. 6,727,704 is jointly owned with the present application and incorporated herein by reference, which proposes a more advanced method for generating homing commands and related information, wherein the location of the target is not limited to being directly below the portable device. Information related to generating the homing command and the homing command itself can be transmitted from the portable device 80 to the drilling tool 20 via signal 99. This information can then be transmitted up the drill string to the drill rig using the drill string transceiver 64 ( FIG. 1 ) and the drill rig transceiver 400 ( FIG. 3 ), allowing the drilling tool to act as a relay. The system 10 also provides for transmitting homing commands and related information to the drill rig using telemetry signals 94 ( FIG. 1 ) received by a telemetry antenna 97 at the drill rig or other suitable location. In another configuration, the portable device may utilize a joystick or other suitable mechanism that enables the operator of the portable device to directly generate drill rig actuation commands. As a non-limiting example, one such device is described in commonly owned U.S. Patent No. 6,079,506 (hereinafter referred to as the '506 patent), which is incorporated herein by reference in its entirety. Specifically, the handheld portable device 140 includes a joystick 148, as shown in FIG. 3 and FIG. 4 of the '506 patent. Using this joystick, any suitable set of drill rig actuation commands can be selectively issued to the operator at the drill rig. Note that the homing command can be generated by either the portable device 80 or the processing device 46 at the drill rig. For the purpose of generating a processing device for a homing command at the drill rig, the portable device can transmit a signal strength reading of the electromagnetic homing signal 66 to the drill rig as a basis for determining the homing command. With this general disclosure at hand, it is believed that one of ordinary skill in the art can readily modify any system that reasonably generates steering mode commands and homing mode commands based on the teachings presented herein.

It is important to understand that the instructions provided to the operator through the user interface ( FIG. 6 ) can be the same regardless of whether the system is in steer mode or home mode. In other words, the appearance of the display in FIG. 6 does not need to be changed in order to switch from steer mode to home mode. The mode switch can be completely transparent to the operator. If desired, "steer" and "home" instructions can be provided on screen 600, although this is not required.

Referring to FIG. 7e , region 700′ is shown in plan view in the XY plane. Region 700′ includes another example of a predetermined drilling plan 704′ leading to a target location T _BP , _which is the endpoint of the drilling plan. The actual path 710′ taken by the drilling tool is represented by a solid line. In this example, drilling plan 704′ may be substantially longer than drilling plan 704 in FIG. 7a , resulting in significantly more accumulated error during the steering mode if compensation is not used. To compensate for or eliminate accumulated error, the portable device 80 may be moved to sequentially define one or more intermediate targets as the drilling tool advances along the device, each of which may be directly on the drilling plan. When the drilling tool approaches a reception range 714′ associated with a first intermediate target I1 while in steering mode, homing mode may be entered at point 760, such that the steering mode then guides the drilling tool to _I1 , eliminating accumulated error. The latter can be seen as an offset between the drilling plan and the actual path at the boundary of the reception range 714′. After the drilling tool passes I ₁ , the system can continue to operate in the homing mode until the drilling tool leaves the reception range 714′ at point 764, whereupon operation switches back to the steering mode. On the segment of the drilling plan that leads from I ₁ to the second intermediate target I ₂ , the figure again shows the accumulated error in the steering mode as a divergence between the actual path and the drilling plan. When the drilling tool approaches the reception range 714″ associated with the second intermediate target I ₂ in the steering mode, the homing mode can be re-entered at point 770, so that the steering mode then guides the drilling tool to I ₂ , continuing to point 774 where the drilling tool leaves the reception range 714″, thereby again eliminating the accumulated error. After passing point 774, the drilling tool advances to the target position T _BP in the manner described above in conjunction with Figure 7a. It will be appreciated that in the example of FIG. 7 e , the endpoints of the drilling plan T _BP coincide with the target position T defined by the portable device, regardless of whether the target position deviates vertically and/or horizontally from the actual physical location of the portable device. In another embodiment, more than one portable device 80 may be used, so that it is not always necessary to move a single portable device to the next intermediate target or final target position. In another embodiment, one or more intermediate targets may be positioned offset from the drilling plan. For example, an obstacle may be discovered directly on the drilling plan that was unknown to the designer of the drilling plan. A series of intermediate targets may be used to guide the drilling tool around the obstacle in a homing mode. After avoiding the obstacle, the drilling tool may return to the drilling plan, for example, using the intermediate targets on the drilling plan, and then continue operating in a steering mode.

7f, a graphical illustration, generally designated by reference numeral 780, is provided to facilitate describing a method for generating a steering indication for returning a drilling tool oriented in a current direction 782 to a drilling path 784. To generate a steering indication for a current position 786 of the drilling tool (FIG. 6), a first step is to determine a desired path 788 having an initial desired orientation 790 that follows a curvature radius R from the current position 786 and the current direction 782 to converge in the correct direction and converge on the drilling plan 784. The current position 786 may be an integrated position based on the integration of pitch and yaw in a steering pattern, or may be determined based on the electromagnetic field 66 emitted from the drilling tool, for example, by moving a portable device above the surface of the earth to identify a point directly above the drilling tool.

Still referring to FIG. 7f , distance "a" is the lateral distance between the current position 786 and the drill plan 784. Distance "b" is the longitudinal distance between the current position 786 and the point 792 where the desired path 788 reaches the drill plan. The desired path 788 from the current position to the drill plan is shown by a dashed line with a curvature radius R. The angle formed between a horizontal line 794 parallel to the drill plan and the desired direction 790 is given by the following equation:

μ＝tan ^-1 (b/a) (9a)

ω＝2μ (9b)

If the current direction 782 of the drilling tool forms an angle λ with respect to the horizontal 794, the turn-indicating parameter is given by Equations 4a-4c, where Δβ or Δφ equals ω - λ, depending on whether the lateral displacement from the drilling plan is in the vertical or horizontal direction. In these determinations, the vertical and horizontal displacements from the drilling plan can be processed separately to determine the desired pitch and yaw changes. In this regard, the plane of the view in FIG. 7f can be a horizontal plane showing a top-down view of the drilling area, or a vertical plane showing the drilling tool in the ground relative to the drilling plan. In another embodiment, the horizontal displacement and desired direction can be determined in three dimensions and then separated into desired pitch and yaw components. This determination can be made to achieve a desired bending radius corresponding to the minimum bending radius of the drill string.

Referring to Figures 7a and 7c, the decision on when to switch from steering mode to homing mode can be determined by a variety of different methods. In one embodiment, the drill operator determines when to switch modes and can manually operate a switch at the drill. In one feature, the option to manually switch to homing mode is only provided when the portable device is within reception range of the drilling tool based on monitoring electromagnetic signal 66. In another embodiment, the portable device 80 can be instructed by its operator to issue a command to a processor at the drill to switch modes. In some embodiments, mode switching can be performed automatically without operator action. In one automatic switching embodiment, switching between modes can be based on the strength of electromagnetic signal 66 measured by the portable device 80, which can be used to determine the distance between the drilling tool and the portable device. In one embodiment, the determination of when to switch between guidance modes (i.e., steering and homing) can be based on only a single distance measurement or on an average of consecutive distance measurements. The determination can also take into account the variance of the consecutive distance measurements, although this is not required. For example, assume that the portable device 80 determines the distance D between the drilling tool and the portable device at regular intervals (e.g., once per second). The mean and standard deviation of a series of N distance measurements D _N are given by:

In equations (10) and (11), _Di is the i-th measurement of distance D, and <D> is the average distance. Switching from steering mode to homing mode can be set to occur when <D><X feet and σ _D <Y feet, where X and Y are thresholds.

In another embodiment, the selection of which mode to use may be determined by selecting the mode that provides the least position uncertainty. In another automatic switching embodiment, switching between the steering mode and the homing mode may combine the guidance information of the two modes weighted by their respective uncertainties. First, define

Δ(X, Y) _homing＝ F (12a)

ΔZ _homing ＝G (12b)

Δ(X,Y)steering=Ψ (12c)

ΔZ _steering = Γ (12d)

Where Δ(X,Y) _homing is the horizontal homing command, ΔZ _homing is the vertical homing command, Δ(X,Y) _steering is the horizontal steering command, and ΔZ _steering is the vertical steering command.

The bootstrap parameters are then weighted by their uncertainties such that

Where is the squared standard deviation of a given parameter (a), Δ(X,Y) in formula (13a) represents the combined horizontal steering command, and ΔZ in formula (13b) represents the combined vertical steering command. It should be understood that the sensor inputs on which the steering command and the homing command are based exhibit a standard deviation, which is reflected as the standard deviation of the steering command and the homing command. When the drilling tool is far away from the locator, the uncertainty in F is much greater than the uncertainty in, so formula (13a) becomes Δ(X,Y)≈ψ. Similarly, when the drilling tool is very close to the portable device, the uncertainty in Ψ is much greater than the uncertainty in, and formula (13a) becomes Δ(X,Y)≈F. Based on the above discussion, it should be clear that the target position can be the end of the entire borehole, or an intermediate target or point along the drilling plan. For example, to complete a 500-foot borehole, the drill operator can place the portable device 80 250 feet from the drill rig and initially drill to the portable device in the manner described above. The operator can then move the portable unit another 250 feet to approach the borehole.

Plan the end target and complete the drilling. One of the 250-foot segments may be a river or road crossing where walking positioning would be impossible or dangerous.

Attention is now directed to FIG8 , which is a flow chart illustrating an embodiment of a method for operating the system 10 , generally designated by reference numeral 800 . The method begins at 802 and proceeds, for example, as described above, to 806 , where a drilling plan is established. At 810 , a drilling array is established. This may include, for example, orienting the drill rig at least approximately in the drilling direction (i.e., along the X-axis) and placing the drilling tool in a starting position. Furthermore, the portable device 80 may be positioned to establish a target position for terminating the drilling run. At 814 , drilling begins by operating in a steering mode. At 818 , a test is performed regarding switching to a homing mode in any suitable manner. In one embodiment, the signal strength of the received electromagnetic signal 66 is periodically tested. The signal strength may be compared to a threshold value, such that once the signal strength exceeds the threshold value, operation will subsequently switch to the homing mode. The test interval may be any suitable value, such as 30 seconds. Embodiments may use a test interval in the range of 1 to 60 seconds. In another embodiment, the test may be based on the mean and standard deviation of a series of N distance measurements D _N according to equations (10) and (11) above. In another embodiment, the test may be based on selecting the mode that provides the smallest position uncertainty. In yet another embodiment, the test may be based on combining the guidance information of the two modes weighted by their respective uncertainties based on equations (12a) to (12d). At 820, the test of step 818 remains in the steering mode by turning to 814 or switches to the homing mode by proceeding to 824. In some embodiments, the portable device may generate an instruction to command the processor on the drilling rig to switch to the homing mode, and this command may be transmitted directly to the drilling rig via telemetry, or by transmitting the command to the drilling tool using signal 99 so that the latter then forwards the command to the drilling rig by transmitting the command up the drill string. At 828, the drilling tool reaches the target position or an intermediate target position. If the drilling tool reaches the target position, the method ends. On the other hand, if the boring tool reaches the intermediate target location, operation may return to the steering mode once the boring tool leaves the reception range of the intermediate target, as shown by dashed line 830. During the operation at step 828, loss of reception of the electromagnetic signal may cause operation to return to the steering mode at 814.

Numerical simulations were performed to estimate the performance of the system 10 operating in the steering mode. For the purpose of the simulations, the following assumptions were made:

Each pipe is 10 feet long.

· A borehole length of 500 feet, and

The operator receives imperfect pitch and yaw information at the start of each pipe, but uses this information perfectly to follow the desired drilling plan - in other words, if the yaw and pitch information were perfect, the user would follow the drilling plan perfectly,

Pitch and yaw information has four possible sources of error:

°Yaw noise,

°Yaw system error,

°Pitch noise, and

° Pitch system error.

The pitch system error is assumed to be zero, and the following values are used for the other three error sources:

Yaw noise standard deviation 0.1 degrees,

Yaw system error 0.046 degrees, and

The standard deviation of pitch noise is 0.007 degrees.

Three sets of simulations were performed based on hypothetical drilling plans, as shown in Figures 9 to 11. Each of these figures schematically illustrates a drilling plan plotted relative to the X-axis, with variations corresponding to the Y-axis indicated using dashed lines and variations corresponding to the Z-axis indicated using solid lines. In Figure 9, a straight drilling plan, generally designated by reference numeral 900, is shown, such that the path between a starting position 904 and a target position 908 in the X/Y plane comprises a straight line. For the purposes of these examples, it is assumed that the target position or endpoint T _BP of the drilling plan coincides with the target position T defined by the portable device. An entry curve and an exit curve can be seen on the Z-axis plot, with a straight line segment 910 formed between the entry and exit curves at approximately -8 feet. Figure 10 illustrates a curved drilling plan, generally designated by reference numeral 1000, such that a curved path 1002 is defined between a starting position 1004 and a target position 1008, as shown in a plan view relative to the Y-axis. The entry and exit curves can be seen on the Z-axis plot and match those of FIG9 with a straight line segment 1010 therebetween at approximately -8 feet. FIG11 shows a curved drill plan, generally indicated by reference numeral 1100, such that a curved path 1102 is defined between a start location 1104 and a target location 1108, as shown in a plan view relative to the Y-axis. The entry and exit curves can be seen on the Z-axis plot and match those of FIG9 and FIG10 with a straight line segment 1110 therebetween at approximately -8 feet, although it should be noted that the vertical scale in FIG11 has been changed to illustrate the relative increased curvature along the Y-axis.

For each of the borehole plans in Figures 9 to 11, a set of simulations was performed. Specifically, 10,000 simulation runs were performed for each borehole plan to determine the mean and standard deviation of the errors in X, Y, and Z. The errors in X, Y, and Z are defined as the difference between the true position at the end of the borehole and the endpoint of the borehole plan. An example of a single simulation run (for the straight borehole plan in Figure 9) is shown in Figure 12. The latter is an error graph, generally indicated by reference numeral 1200, showing the error in X (shown as a dashed line 1202), the error in Y (shown as a dashed line 1206), and the error in Z (shown as a solid line 1208) plotted against the X-axis. In the simulation corresponding to Figure 12, the errors in X, Y, and Z at the end of the borehole were approximately 0.02', 0.01', and -0.2', respectively.

Table 1 below provides the mean and standard deviation of the cumulative position errors in X, Y, and Z for the straight numerical simulation drilling plan 900 in FIG. 9 , the first curved numerical simulation drilling plan 1000 in FIG. 10 , and the second curved numerical simulation drilling plan in FIG. 11 .

Table 1 – Drilling plan numerical simulation

For all simulated bore plans, the cumulative position errors in the X and Z axes were negligible. The cumulative position error along the Y axis was approximately 5 inches for the straight bore plan 900 and the first curved bore plan 1000, and approximately 12 inches for the second curved bore plan 1100. It should be appreciated that all of these cumulative position errors are sufficiently small that, when the transmitter reaches the receiving range of the portable device 80 and switches to the homing position, the operator can effectively steer to the target position based on the homing command to correct the position errors accumulated during the steer mode. Even for the second curved bore 1100, the transmitter was within 2 feet of the target position 95% of the time (mean plus two standard deviations). Typically, the homing operation can be initiated once the drilling tool reaches 35 feet from the portable device. Correcting a 2-foot error starting at 35 feet from the portable device requires a pipe bend radius of approximately 300 feet, a reasonable amount of bend for standard 2.375-inch drill pipe.

In view of the above, the present disclosure at least provides:

The ability to perform HDD (Horizontal Directional Drilling) crossings, i.e. drilling below areas where conventional walking positioning is not possible, and correcting for the positional errors that inevitably accumulate, and

The ability to drill without a walking position operator, thereby freeing up skilled workers to perform other duties. This is facilitated at least in part by a system architecture that uses the drill string as an electrical conductor to transmit data from the drilling tool to the drill rig, at least during steering mode, as described in further detail below.

The present disclosure combines steering tool functionality, guidance using pitch and yaw sensors, and drill path determination with homing. Switching between steering and homing modes is performed automatically using the same user interface, so the operation is the same as conventional homing.

The foregoing description of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other embodiments, modifications, and variations may be implemented in light of the above teachings, wherein those skilled in the art will recognize certain modifications, permutations, additions, and sub-combinations thereof.

Preferably, all elements, components and steps described herein are included. It should be understood that it is obvious to a person skilled in the art that any of these elements, components and steps can be replaced by other elements, components and steps or deleted altogether. In broad terms, at least the following is disclosed herein: a drilling tool that moves through the earth. A transmitter supported by the drilling tool sends an electromagnetic homing signal. A portable device monitors the electromagnetic homing signal in a homing mode and receives the electromagnetic homing signal to guide the drilling tool to a target position. In a steering mode, a processor generates a steering command to guide the drilling tool based on the drilling plan so as to introduce at least a certain position error without using the electromagnetic homing signal. The switch from the steering mode to the homing mode is based on monitoring the homing signal when the drilling tool approaches the portable device, and then guiding the drilling tool to the target position to compensate for the position error. An intermediate target position is described, and the drilling tool is guided based on the homing signal as long as the portable device receives the signal.

concept

This article discloses at least the following concepts:

Concept 1. An apparatus forming part of a system comprising a boring tool movable by a drill string having an extendable length, the drill string being directed from a drilling rig to the boring tool for performing a horizontal directional drilling operation of advancing the boring tool through the earth, the apparatus comprising:

a transmitter supported by the drilling tool for transmitting an electromagnetic homing signal, the transmitter comprising a magnetometer for generating magnetic readings representative of the Earth's magnetic field and an accelerometer for generating pitch readings representative of the pitch orientation of the drilling tool; a portable device configured to monitor the electromagnetic homing signal in a homing mode and to receive the electromagnetic homing signal for use in generating a homing command to guide the drilling tool to a target location relative to the portable device; and

a processor configured to generate a steering command to guide the drilling tool in a steering mode based on a drilling plan using the magnetic readings, the pitch readings, and the extendable length of the drill string so as to introduce at least some position error between the actual position of the underground tool and the predicted position of the underground tool, and to switch from the steering mode to the homing mode based at least in part on monitoring the electromagnetic homing signal when the drilling tool approaches the portable device and thereafter moves the drilling tool to the target position to compensate for the position error.

Concept 2. The device of Concept 1 wherein said homing mode is manually selectable by an operator when said portable device is within receiving range of said drilling tool.

Concept 3. The apparatus of Concept 1 or 2, wherein the processing device is configured to automatically switch to the homing mode upon entering within a receiving range of the drilling tool.

Concept 4. The apparatus of Concepts 1-3, wherein said drilling tool is configured to transmit said pitch readings and said magnetic readings to said drill rig during said steering mode using said drill string as an electrical conductor.

Concept 5. The device of Concepts 1-4, wherein said portable device is configured to determine a signal strength of said electromagnetic homing signal.

Concept 6. The device of Concept 5 wherein one of said processor and said portable device is configured to compare said signal strength to a signal strength threshold as part of switching from said steering mode to said homing mode.

Concept 7. The apparatus of Concepts 1-6, wherein said processor is configured to operate in said steering mode based on said magnetic readings, said pitch readings, and said extendable length of said drill string without using said homing signal, and to operate in said homing mode based at least in part on detection of said electromagnetic homing signal.

Concept 8. The device of Concepts 1-6, wherein said processor is configured to blend said homing command with said steering command as said drilling tool approaches said portable device.

Concept 9. The apparatus of Concept 8 wherein said blending weights said homing command and said steering command based on an uncertainty associated with each of said homing command and said steering command.

Concept 10. The apparatus of Concept 9 wherein said uncertainty is based on a standard deviation of said homing command and a standard deviation of said steering command.

Concept 11. The device of Concept 9 wherein said homing command is incrementally weighted based on increasing signal strength of said electromagnetic homing signal received by said portable device.

Concept 12. The device of Concept 1-11 wherein said portable device generates said homing command.

Concept 13. The apparatus of Concept 1-11 wherein said processor generates said homing command.

Concept 14. The apparatus of Concepts 1-11 wherein said processor is located at said drilling rig.

Concept 15. A method for use with a system comprising a boring tool movable by a drill string having an extendable length, the drill string being directed from a drill rig to the boring tool for performing a horizontal directional drilling operation of advancing the boring tool through the earth, the method comprising:

generating a steering command in a steering mode for guiding the drilling tool in the steering mode based on a drilling plan using magnetic and pitch readings extracted by the drilling tool in combination with an extendable length of the drill string to introduce at least some positional error between an actual position of the inground tool and a predicted position of the inground tool;

monitoring an electromagnetic homing signal emitted from the drilling tool proximate a target location;

automatically switching from the steering mode to a homing mode based on detection of the electromagnetic homing signal when the drilling tool approaches the target location; and

Thereafter, the drilling tool is guided to the target position to compensate for the position error using a homing command based at least in part on the detection of the electromagnetic homing signal.

Concept 16. An apparatus forming part of a system comprising a boring tool movable by a drill string having an extendable length, the drill string being directed from a drilling rig to the boring tool for performing a horizontal directional drilling operation of advancing the boring tool through the earth, the apparatus comprising:

a transmitter supported by the drilling tool for transmitting an electromagnetic homing signal, the transmitter comprising a magnetometer for generating magnetic readings representative of the Earth's magnetic field and an accelerometer for generating pitch readings representative of the pitch orientation of the drilling tool; a portable device comprising an antenna configured to receive the electromagnetic homing signal to generate electromagnetic information when the portable device is within a receiving range of the transmitter; and

a processing device configured to generate a steering command for guiding the drilling tool in a steering mode based on a drilling plan using the magnetic readings, the pitch readings, and the extendable length of the drill string so as to introduce at least a position error between the actual position of the underground tool and the predicted position of the underground tool, and to guide the drilling tool to a target position relative to the portable device in a homing mode to compensate for the position error when the portable device is within the receiving range.

Concept 17. The device of Concept 16, wherein an operator can manually select said homing mode to switch to said homing mode when said portable device is within receiving range of said drilling tool.

Concept 18. The apparatus of Concept 16 or 17, wherein the processing device is configured to automatically switch to the homing mode upon entering a receiving range from the drilling tool.

Concept 19. An apparatus forming part of a system comprising a boring tool movable by a drill string having an extendable length, the drill string being directed from a drilling rig to the boring tool for performing a horizontal directional drilling operation of advancing the boring tool through the earth, the apparatus comprising:

a transmitter supported by the drilling tool for transmitting an electromagnetic homing signal, the transmitter comprising a magnetometer for generating magnetic readings representative of the Earth's magnetic field and an accelerometer for generating pitch readings representative of the pitch orientation of the drilling tool; a portable device comprising an antenna configured to receive the electromagnetic homing signal to generate electromagnetic information when the portable device is within a receiving range of the transmitter; and

a processing device configured to generate a steering command for guiding the drilling tool in a steering mode based on a drilling plan using the magnetic readings, the pitch readings, and the extendable length of the drill string so as to introduce at least a position error between the actual position of the underground tool and the predicted position of the underground tool, and for guiding the drilling tool in a homing mode at least approximately back to the drilling plan when the portable device is within the receiving range.

Concept 20. The apparatus of Concept 19, wherein said processing device directs said drilling tool back to said drilling plan based on an intermediate target associated with said portable device defined at an intermediate position along said drilling plan.

Concept 21. The apparatus of Concept 20 wherein said processing device is configured to initially guide said drilling tool to said intermediate target.

Concept 22. An apparatus according to Concept 20 or 21, characterized in that the processing device is configured to continue guiding the drilling tool along the drilling plan in the homing mode after the drilling tool passes the intermediate target as long as the portable device is within the receiving range of the transmitter.

Concept 23. The apparatus of Concept 22 wherein said processing device is configured to revert to said steering mode to continue guiding said drilling tool along said drilling plan after said receiving range has been exceeded.

Claims (21)

1. An apparatus for a multi-mode steering and homing system, the system comprising a drilling tool that moves via a drill string having an extended length, the drill string being guided from a drilling rig to the drilling tool for performing a horizontal directional drilling operation that advances the drilling tool through the ground, characterized in that the apparatus comprises: A transmitter for transmitting electromagnetic homing signals, supported by the drilling tool, the transmitter including a magnetometer for generating magnetic readings characterizing the Earth's magnetic field and an accelerometer for generating pitch readings characterizing the pitch orientation of the drilling tool. A portable device configured to monitor the electromagnetic homing signal in homing mode and to receive the electromagnetic homing signal for use in generating a homing command to guide the drilling tool to a target location associated with the portable device, wherein monitoring the electromagnetic homing signal includes determining the signal strength of the electromagnetic homing signal; and A processor is configured to generate steering commands to guide the drilling tool in steering mode based on the drilling plan using the magnetic readings, the pitch readings, and the length of the drill string extension, such that at least some position error is introduced between the actual position of the drilling tool and the predicted position of the drilling tool, and to switch from the steering mode to the homing mode at least in part based on monitoring the electromagnetic homing signal when the drilling tool approaches the portable device and is subsequently moved to the target position to compensate for the position error, and one of the processor and the portable device is configured to compare the signal strength with a signal strength threshold as part of the switch from the steering mode to the homing mode. 2. The apparatus for a multi-mode steering and return system according to claim 1, characterized in that, when the portable device is within the receiving range of the drilling tool, the return mode can be manually selected by the operator. 3. The apparatus for a multi-mode steering and homing system according to claim 1, wherein the processing device is configured to automatically switch to the homing mode when entering the receiving range of the drilling tool. 4. The apparatus for a multi-mode steering and homing system according to claim 1, wherein the drilling tool is configured to use the drill string as an electrical conductor to transmit the pitch reading and the magnetic reading to the drilling rig during the steering mode. 5. The apparatus for a multi-mode steering and return system according to claim 1, wherein the portable device generates the return command. 6. The apparatus for a multi-mode steering and return system according to claim 1, wherein the processor generates the return command. 7. The apparatus for a multi-mode steering and homing system according to claim 1, wherein the processor is located at the drilling rig. 8. An apparatus for a multi-mode steering and homing system, the system comprising a drilling tool that moves via a drill string having an extended length, the drill string being guided from a drilling rig to the drilling tool for performing a horizontal directional drilling operation that advances the drilling tool through the ground, characterized in that the apparatus comprises: A transmitter for transmitting electromagnetic homing signals, supported by the drilling tool, the transmitter including a magnetometer for generating magnetic readings characterizing the Earth's magnetic field and an accelerometer for generating pitch readings characterizing the pitch orientation of the drilling tool. A portable device configured to monitor the electromagnetic homing signal in homing mode and to receive the electromagnetic homing signal for use in generating a homing command to guide the drilling tool to a target position associated with the portable device; and A processor is configured to generate steering commands to guide the drilling tool in a steering mode based on a drilling plan using the magnetic readings, the pitch readings, and the length of the drill string extension, such that at least some positional error is introduced between the actual position of the drilling tool and the predicted position of the drilling tool, and to switch from the steering mode to the homing mode, at least partially based on monitoring the electromagnetic homing signal, when the drilling tool approaches the portable device and is subsequently moved to the target position to compensate for the positional error. The processor is configured to operate in the steering mode based on the magnetic readings, the pitch readings, and the length of the drill string extension without using the homing signal, and to operate in the homing mode at least partially based on the detection of the electromagnetic homing signal. 9. An apparatus for a multi-mode steering and homing system, the system comprising a drilling tool that moves via a drill string having an extended length, the drill string being guided from a drilling rig to the drilling tool for performing a horizontal directional drilling operation that advances the drilling tool through the ground, characterized in that the apparatus comprises: A transmitter for transmitting electromagnetic homing signals, supported by the drilling tool, the transmitter including a magnetometer for generating magnetic readings characterizing the Earth's magnetic field and an accelerometer for generating pitch readings characterizing the pitch orientation of the drilling tool. A portable device configured to monitor the electromagnetic homing signal in homing mode and to receive the electromagnetic homing signal for use in generating a homing command to guide the drilling tool to a target position associated with the portable device; and A processor configured to generate steering commands to guide the drilling tool in steering mode based on the drilling plan using the magnetic readings, the pitch readings, and the length of the drill string extension, such that at least some positional error is introduced between the actual position of the drilling tool and the predicted position of the drilling tool, and to switch from the steering mode to the homing mode, at least in part based on monitoring the electromagnetic homing signal, when the drilling tool approaches the portable device and is subsequently moved to the target position to compensate for the positional error, the processor being configured to mix the homing command with the steering command when the drilling tool approaches the portable device. 10. The apparatus for a multi-mode steering and return system according to claim 9, wherein the mixing weights the return command and the steering command based on uncertainties associated with each of the return command and the steering command. 11. The apparatus for a multi-mode steering and return system according to claim 10, wherein the uncertainty is based on the standard deviation of the return command and the standard deviation of the steering command. 12. The apparatus for a multi-mode steering and return system according to claim 10, wherein the return command is based on an incrementally weighted sum of the incremental signal strengths of the electromagnetic return signal received by the portable device. 13. A method for a multi-mode steering and homing system, the system comprising a drilling tool that moves via a drill string having an extended length, the drill string being guided from a drilling rig to the drilling tool for performing a horizontal directional drilling operation that advances the drilling tool through the ground, characterized in that the method comprises: In steering mode, a steering command is generated to guide the drilling tool in steering mode using magnetic and pitch readings extracted by the drilling tool in combination with the length of the drill string extension based on the drilling plan, so as to introduce at least some positional error between the actual position of the drilling tool and the predicted positioning of the drilling tool. Monitoring electromagnetic homing signals emitted from the drilling tool near the target location, including determining the signal strength of the electromagnetic homing signals; When the drilling tool approaches the target position, based on the detection of the electromagnetic homing signal, including comparing the signal strength with a signal strength threshold, it automatically switches from the steering mode to the homing mode; and Subsequently, the drilling tool is guided to the target position using a homing command based at least in part on the detection of the electromagnetic homing signal to compensate for the position error. 14. An apparatus for a multi-mode steering and homing system, the system comprising a drilling tool that moves via a drill string having an extended length, the drill string being guided from a drilling rig to the drilling tool for performing a horizontal directional drilling operation that advances the drilling tool through the ground, characterized in that the apparatus comprises: A transmitter for transmitting electromagnetic homing signals, supported by the drilling tool, the transmitter including a magnetometer for generating magnetic readings characterizing the Earth's magnetic field and an accelerometer for generating pitch readings characterizing the pitch orientation of the drilling tool. A portable device including an antenna configured to receive the electromagnetic homing signal to generate electromagnetic information when the portable device is within receiving range of the transmitter, including determining the signal strength of the electromagnetic homing signal; and A processing device is configured to generate a steering command to guide the drilling tool in a steering mode based on the drilling plan using the magnetic reading, the pitch reading, and the length of the drill string extension, such that at least some positional error is introduced between the actual position of the drilling tool and the predicted positioning of the drilling tool, and to guide the drilling tool to a target position associated with the portable device in a homing mode to compensate for the positional error when the portable device is within the receiving range, and one of the processing device and the portable device is configured to compare the signal strength with a signal strength threshold as part of switching from the steering mode to the homing mode. 15. The apparatus for a multi-mode steering and return system according to claim 14, characterized in that, when the portable device is within receiving range of the drilling tool, the operator can manually select the return mode to switch to the return mode. 16. The apparatus for a multi-mode steering and homing system according to claim 14, wherein the processing device is configured to automatically switch to the homing mode when entering the receiving range from the drilling tool. 17. An apparatus for a multi-mode steering and homing system, the system comprising a drilling tool that moves via a drill string having an extended length, the drill string being guided from a drilling rig to the drilling tool for performing a horizontal directional drilling operation that advances the drilling tool through the ground, characterized in that the apparatus comprises: A transmitter for transmitting electromagnetic homing signals, supported by the drilling tool, the transmitter including a magnetometer for generating magnetic readings characterizing the Earth's magnetic field and an accelerometer for generating pitch readings characterizing the pitch orientation of the drilling tool. A portable device including an antenna configured to receive the electromagnetic homing signal to generate electromagnetic information when the portable device is within receiving range of the transmitter, including determining the signal strength of the electromagnetic homing signal; and A processing device is configured to generate a steering command to guide the drilling tool in a steering mode based on the drilling plan using the magnetic reading, the pitch reading, and the length of the drill string extension, such that at least some positional error is introduced between the actual position of the drilling tool and the predicted position of the drilling tool, and to guide the drilling tool in a homing mode, at least approximately, back to the drilling plan when the portable device is within the receiving range, and one of the processing device and the portable device is configured to compare the signal strength with a signal strength threshold as part of switching from the steering mode to the homing mode. 18. The apparatus for a multi-mode steering and return system according to claim 17, wherein the processing device guides the drilling tool back to the drilling plan based on an intermediate target defined in relation to the portable device at an intermediate position along the drilling plan. 19. An apparatus for a multi-mode steering and homing system, the system comprising a drilling tool that moves via a drill string having an extended length, the drill string being guided from a drilling rig to the drilling tool for performing a horizontal directional drilling operation that advances the drilling tool through the ground, characterized in that, A transmitter for transmitting electromagnetic homing signals, supported by the drilling tool, the transmitter including a magnetometer for generating magnetic readings characterizing the Earth's magnetic field and an accelerometer for generating pitch readings characterizing the pitch orientation of the drilling tool. A portable device including an antenna configured to receive the electromagnetic homing signal to generate electromagnetic information when the portable device is within receiving range of the transmitter; and A processing device configured to generate a steering command to guide the drilling tool in a steering mode based on the drilling plan using the magnetic reading, the pitch reading, and the length of the drill string extension, such that at least some positional error is introduced between the actual position of the drilling tool and the predicted positioning of the drilling tool, and to guide the drilling tool in a homing mode to a target position associated with the portable device to compensate for the positional error when the portable device is within the receiving range, the processing device being configured to initially guide the drilling tool to an intermediate target at an intermediate position along the drilling plan. 20. The apparatus for a multi-mode steering and homing system according to claim 19, wherein the processing apparatus is configured to continue guiding the drilling tool along the drilling plan in the homing mode, provided that the portable device is within the receiving range of the transmitter after the drilling tool has passed the intermediate target. 21. The apparatus for a multi-mode steering and return system according to claim 20, wherein the processing device is configured to return to the steering mode after exceeding the receiving range to continue guiding the drilling tool along the drilling plan.