Horizontal Directional Drilling Guidence System

Abstract

The present invention is a navigation system for Horizontal Directional Drilling (HDD) that provides subsurface navigation, guidance, and steering for drilling boreholes. The system includes a non-magnetic drill pipe with rotating magnets (rotating rare earth magnets) and at least one surface sensor station. The system may include a driller's display, a steering hand computer (a laptop or office PC), a wireless drill rig sensor, and a cloud data server connection. The rotating magnet (rotating rare earth magnets) acts as a navigational beacon or subsurface beacon and the surface sensor station monitors and tracks the subsurface rotating magnets and reports the information over a radio network. Further, the invention includes navigation algorithms that utilize a Kalman filter that combines dead reckoning and magnetic ranging computations to provide more accurate borehole positions.

Description

[0001] This utility patent application is a Continuation-In-Part (CIP) of patent application Ser. No. 18 / 990,564, filed on Dec. 20, 2024, by the subject inventor. The earlier application was assigned to Art Unit 36782, Examiner Taras P. BemkoFIELD OF THE INVENTION

[0002] The present invention relates to the field of borehole drilling, and more particularly, to a Horizontal Directional Drilling (HDD) guidance and navigation system for drilling boreholes using rotating magnets.BACKGROUND OF THE INVENTION

[0003] Horizontal Directional Drilling (HDD) techniques are widely recognized for creating boreholes beneath both man-made and natural obstacles. These include bodies of water like rivers or lakes, as well as beneath highways, airport runways, and residential areas. HDD is specifically employed for installing various utilities, including gas pipelines, electrical lines, underground transmission lines, communication cables, water pipes, and sewer pipes.

[0004] There are several apparatus and methods for HDD are known in the prior art. FIG. 1 illustrates a typical configuration for drilling bore hole using HDD. Pipe installation by HDD is generally carried out in stages, where the first stage consists of drilling a small diameter pilot hole along the designed direction path, and the second stage involves pulling the drill pipe back out of the hole while pulling the new utility into the hole via the pilot hole exit. A reamer is often used during pullback to enlarge the pilot hole for the new utility. As shown in FIG. 1, the pilot hole is drilled along a preplanned alignment where the entry and exit points are located using traditional above-ground survey methods. The drilling machine forces a drill pipe into the subsurface, and successively adds sections of drill pipe as the bore is advanced. Larger machines use a hydraulic mud motor near the bit to turn it, while smaller rigs turn the entire drill pipe to rotate the bit. Drilling mud is pumped through the hollow drill pipe to provide lubrication and spoils removal at the bit, which then flows along the annulus outside the drill pipe and returns to the drill rig. FIG. 2 illustrates a Bottom Hole Assembly (BHA) known in the prior art which contains the bit, a bent sub that can be directed for steering, and an instrumented steering tool to provide navigation and steering feedback.

[0005] Larger drill rigs used for utilities and river crossing applications incorporate downhole instrument packages that provide steering feedback to the driller. This procedure often utilizes drill string accelerometers or inclinometers to measure the roll and pitch of the drill bit. The tool face measurement is derived from roll and indicates the direction of curvature for the advancing drill. Yaw is measured by sensing the earth's magnetic field through magnetometers or using a north-seeking gyro. These measurements are sent to the surface using a suitable telemetry system where they are analyzed to provide steering feedback to the drill operators. Starting with a known bit position (i.e. the entry point of the boring), a dead reckoning method uses the bit's measured orientation to calculates the new position as the drill pipe advances a known distance (such as the drill pipe length). Challenges with this method are that it is difficult to measure yaw accurately using the earth's magnetic field, that errors accumulate during the drilling process, and that a telemetry system is needed. Gyros, while effective, are expensive, prone to measurement drift, and too bulky for smaller drill rigs.

[0006] Larger drill rigs in river crossing applications may use a magnetic beacon on the surface for determining the position of the drill bit. These beacons are generated using electric currents in coils or wires at the surface, with the corresponding magnetic fields measured by drill string magnetometers positioned just behind the bit. The position of the bit relative to the beacons can be calculated from the magnetometer measurements. This magnetic ranging method performs well but necessitates a downhole instrument package and a suitable telemetry system to transmit sensor measurements for ranging calculations at the surface. The layout of magnetic guidance wires (commercially known as the TruTrack and ParaTrack methods) is a time consuming operation requiring trained personnel. In many cases this operation must be repeated daily to avoid theft. Beacon wires cannot be deployed across railway lines, roadways, and private property. They are very difficult to deploy in rough topography, marshy areas, or in areas covered by water.

[0007] Large drill rigs in the river crossing industry typically employ downhole sensor packages and telemetry systems to send sensor data to the surface. Wireless telemetry technologies like mud-pulse or electromagnetic (EM) telemetry have been utilized in the oil and gas industries, their high cost and slow data rates hinder real-time steering feedback in river crossing applications. Mud-pulse telemetry involves sending pressure pulses through drilling mud in the string, while EM telemetry drives current across a gap-sub near the bit, creating an electric field disturbance detected at the surface using an array of electrodes. Implementing EM telemetry in urban areas faces challenges due to ambient EM noise and limited unpaved areas for electrode placement. In contrast, wired telemetry offers fast data rates, but requires adding a new wired connection for every drill rod. This method is time-consuming, often unreliable, and susceptible to insulation breaches leading to short circuits.

[0008] Smaller HDD rigs for shallow utility installation commonly employ a battery powered magnetic beacon near the bit, which is detected by surface magnetometers packaged in a handheld walkover receiver device. These walkover receivers utilize antennas or coils (unlike the flux-gate magnetometers used in this disclosed invention). The beacon's coils are energized with an AC current within specific frequency ranges where ambient magnetic interference is minimal. The beacon assembly also contains sensors for tool face and inclination readings, which are transmitted to the walkover receiver by modulating the magnetic field. Magnetic ranging algorithms determine the beacon's location, while tool face and inclination readings guide the driller. Some limitations of these systems are that the beacon's strength and detectable range are constrained by battery size limitations on the drill string. The power consumption of the beacon must be limited so that battery power lasts while the entire hole is bored, and the operating time of a downhole beacon is typically limited to a few days. Furthermore, moving the walkover receiver to a position over the bit can be challenging due to terrain access limitations, and the limited functional range (typically 30-40 meters) restricts drilling depth (while the solution describe herein increases this range to over 100 meters).

[0009] Rotating magnets have been used in BHAs for steering command systems and methods that allow the driller to set the direction in which the drill string is advancing. They do not provide any informational feedback regarding the subsurface drill location or direction of advance (i.e. drill string inclination or azimuth).

[0010] When drilling near an existing well, a magnetic beacon can be placed in the adjacent well for use in navigation and ranging. Generally some type of magnetic beacon or tracer signal is placed on the nearby well, or magnetic sensors are used to detect the magnetic signature of the nearby well. This method is usually used in oil and gas fields at depths of a few kilometers and is not conducive to HDD borings where a nearby well is not present.

[0011] Two-dimensional (2D) rotating magnet tracking systems and methods employ a rotating magnet in the drill string and estimate position using 2D triangulation in the plane defined by the axis of rotation of the drill. The method does not measure the magnet's position in the third dimension (3D), is unable to detect when the dipole axis of rotation changes, and requires a known starting position. It is not suitable to HDD drill paths where the axis of rotation changes markedly over the trajectory of the boring. Shortcomings to this method are that it requires continuous rotation of the drill string, the accuracy diminishes as the rotation axis deviates from the initial direction, and the method requires two or more magnetometer sensors at two or more locations for two-dimensional tracking.

[0012] Dead reckoning methods use a downhole instrument package to measure the orientation of the drill pipe just behind the bit, and then integrate position as the drill string advances into the subsurface. Tool face and inclination (i.e., roll and pitch) are measured using accelerometers (or inclinometers) and yaw is determined by either measuring the Earth's magnetic field with magnetometers or by measuring the Earth's rotation using gyros. A telemetry system is needed to send information from the downhole sensors to the surface for analysis. The biggest issue with dead reckoning methods is that errors accumulate, and the farther the drill string advances into the hole the larger the positional uncertainty becomes.

[0013] The navigation systems described above do not make use of simultaneously available navigation information. They simply employ either dead-reckoning, magnetic ranging, or triangulation. A combination of these techniques provides a more accurate location estimate. In contrast, the present invention incorporates a Kalman filter that combines both magnetic ranging and dead reckoning techniques to provide a more accurate estimate than the sole use of magnetic ranging and / or dead reckoning. The filter can further constrain the estimated position by incorporating the pipe payout and tool face measurements along with the curvature allowed by the drill pipe.

[0014] On HDD jobsites, equipment can be spread out over the site and be used by several different individuals. Collecting data from all of the equipment and operators can be cumbersome and error prone. Data examples include data streams from walkover receivers, the GPS location of the entry pit, surface beacon wire locations, and surface features such as water boundaries, and obstacle locations that need to be considered before drilling. The use of radio data links between the various pieces of equipment combined with a data repository would enhance the accuracy, efficiency, and data management capabilities of the drilling process.SUMMARY OF THE INVENTION

[0015] Aspects of the present invention provide a HDD guidance and navigation system.

[0016] In one aspect the present invention provides subsurface navigation, guidance, and steering feedback for use in HDD operations.

[0017] In one aspect the present invention includes a non-magnetic drill pipe with integrated magnets that rotate with the pipe (rotating rare earth magnets), and at least one surface sensor station.

[0018] In one aspect the present invention includes a downhole assembly with orientation sensors, a motor driven rotating magnet (rotating rare earth magnet), and one or more surface sensor stations.

[0019] In one aspect the present invention, strong magnetic beacons are provided by rare earth magnets that offer increased range capability over conventional walkover systems. The rotating magnet acts as a subsurface navigational beacon which produces a magnetic moment that is significantly stronger (typically 500 to 2500 A-m2) than the those produced by systems using a battery powered downhole coil and walkover detector (typically 10 to 50 A-m2). The increased strength allows for the stationary magnetometer to be placed on the surface over the general vicinity of the subsurface beacon, and the range between the surface sensor station and the drill bit can be as large as 150 m. This allows a stationary placement of the surface station and eliminates the need of having an operator continually move the walkover sensor to be within range of a conventional walk-over beacon. Surface sensor stations may only need to be moved a few times for the entire job.

[0020] In one aspect the present invention provides an implementation of the use of rotating rare earth magnetic beacons on the drill string, a magnetometer at a known position on the surface, and three-dimensional analysis routines that determine the location and orientation of the subsurface magnetic beacon.

[0021] In one aspect the present invention includes one or more surface sensor stations. The surface sensor station consists of an embedded computer, a radio network link, an RTK GPS (real-time kinematic global positioning system) receiver system, and at least one three-component flux-gate magnetometer. The surface sensor station monitors and tracks the subsurface rotating magnet (beacon) and reports the information over the radio network. The surface sensor stations are man-portable and easy to deploy, and can detect the subsurface magnetic beacon from a long range, which allows an unmanned station to be placed along the drill path and only moved a few times for the entire job. A worker that continuously moves a walkover receiver over the beacon is not needed. Navigation is possible in locations where a walkover receiver is impractical (marshy areas, limited access land, etc.

[0022] In one aspect the present invention provides a more precise navigation method using a Kalman filter that combines magnetic ranging and dead reckoning techniques to provide more accurate drill string position positions. The method integrates drill rod payout and previous location estimates together with location estimates from magnetic beacon tracking to obtain a more precise position.

[0023] In one aspect the present invention includes drill rig sensor that measures the pipe payout and rotation angle.

[0024] In one aspect the present invention includes a wireless radio network that provides data communications links between system components including surface sensor stations, driller's display, steering hand computer, a drill rig pipe sensor, and an optional cloud data server. These radio data links combines WiFi radios (high bandwidth with 100 m range typical), LORA radios (low bandwidth with 1.5 km range typical), and cellular data links. These data links provide data sharing between the various nodes in the system (i.e., surface stations, drill rig pipe sensor, and a cloud data server). One node serves as a central hub for routing traffic between the other nodes. Radio data links are provided on the surface sensor stations, the drill rig pipe sensor, the driller's display, and the steering hand computer.

[0025] In one aspect of the invention, a subsurface telemetry system is used to send data from the BHA to a surface sensor station. The telemetry system modulates the rotation rate of the motor driven rotating magnet to send data from the BHA to the surface sensor stations.

[0026] In one aspect the present invention includes a driller's display (such as a tablet PC), and / or steering hand computer (a laptop or office PC), one or more surface sensor stations, and an optional cloud data server connection.

[0027] In one aspect of the invention, the system provides steering feedback to the drill operator. More specifically, the tool face, azimuth, and inclination of the drill rod is provided using one of several methods. First, the sensed magnetic field generated by the rotating beacon can be used to determine tool face and inclination. Alternatively, tool face and inclination are determined using tilt or accelerometer sensor on the BHA, and these values are sent to the surface using the subsurface telemetry system.

[0028] In one aspect of the present invention the HDD guidance and navigation system eliminates the need for fragile downhole electronics.

[0029] In one aspect of the present invention the HDD guidance and navigation system eliminates the need for downhole batteries which may limit the duration of the drilling job.

[0030] The summary of the invention is not intended to limit the key features and essential technical features of the claimed invention, and is not intended to limit the scope of protection of the claimed embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The object of the invention may be understood in more details, and more particularly description of the invention briefly summarized below by reference to certain embodiments thereof which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the appended drawings illustrate preferred embodiments of the invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective equivalent embodiments.

[0032] FIG. 1 illustrates a typical configuration for drilling borehole using horizontal directional drilling (HDD) known in the prior art;

[0033] FIG. 2 illustrates a Bottom Hole Assembly (BHA) known in the prior art;

[0034] FIG. 3 illustrates a HDD guidance and navigation system for drilling boreholes, according to an embodiment of the present invention;

[0035] FIG. 4 illustrates a surface sensor station for reporting position and orientation of a subsurface magnetic beacon on a drill string, according to an embodiment of the present invention;

[0036] FIG. 5a illustrates a configuration with a set of rotating magnets added to a drill pipe on the Bottom Hole Assembly (BHA), according to an embodiment of the present invention;

[0037] FIG. 5b illustrates a set of rotating magnets inside a drill pipe whose orientation is controlled by downhole electronics, according to an embodiment of the present invention;

[0038] FIG. 5c shows a sectional view of FIG. 5b, according to an embodiment of the present invention; and

[0039] FIG. 6 depicts a drill site, according to an embodiment of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0040] The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which a preferred embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiment set forth herein. Rather, the embodiment is provided so that this disclosure will be thorough, and will fully convey the scope of the invention to those skilled in the art.

[0041] As described herein with several embodiments, FIG. 3 illustrates a HDD guidance and navigation system 10 of the present invention that combines one or more of the technologies including rotating magnets (rotating rare earth magnets) 12, one or more surface sensor stations 14, three-dimensional tracking routines 28, a driller's display 16, a drill rig pipe sensor 18, a radio network 22, navigation and steering algorithms 30, and a cloud data server 20.

[0042] In one embodiment, the HDD guidance and navigation system 10 includes a non-magnetic drill pipe with rotating magnets (rotating rare earth magnets) 12, a surface sensor station 14, three-dimensional tracking routines 28, navigation and steering algorithms 30, and a driller's display (a tablet PC) 16.

[0043] In one embodiment, the HDD guidance and navigation system 10 may include a motor driven rotating magnet (rotating rare earth magnet) 12, downhole orientation sensors 24, a subsurface telemetry system 26, one or more surface sensor stations 14, three-dimensional tracking routines 28, a drill rig pipe sensor 18, navigation and steering algorithms 30, a driller's display (a tablet PC) 16, a steering hand computer (a laptop or office PC), a radio network 22, and a cloud data server 20.

[0044] As illustrated in FIG. 4, the surface sensor station 14 consists of an embedded computer 42, a radio data link 44, an RTK GPS (real-time kinematic global positioning system) receiver system 46, and at least one three-component flux-gate magnetometer 48. The surface sensor station monitors and tracks the subsurface rotating magnet (beacon) 12 and reports the information over the radio network22.

[0045] In one embodiment, the radio data link 44 combines WiFi radio (high bandwidth with 100 m range typical), LORA radio (low bandwidth with 1.5 km range typical), and cellular data links to connect with other nodes on the job site that may include additional surface sensor stations 14, the driller's display 16, drill rig pipe sensor 18, a steering hand's computer, and a data server in the cloud 20. In this network, one node is chosen as the central hub for dispatching messages between the nodes.

[0046] In an embodiment for small drill rigs, the rotating magnets 12 units are positioned near the drill bit and serve as a subsurface navigational beacon. Consequently, no downhole electronics are necessary for this configuration. Pipe rotation (and subsequently beacon rotation) is a standard practice during drilling, utilized for following a straight trajectory or employing a carving technique to navigate along a curved path. The surface sensor station 14, utilizes the magnetometer 48 to capture signals produced by the subsurface beacon. These readings play a crucial role in estimating both the position and orientation of the beacon as well as the drill string.

[0047] In an embodiment for larger drill rigs, the electric motor driven rotating magnets 12 are positioned near the drill bit, and serve both as a subsurface magnetic beacon and as a telemetry system for transmitting sensor data. Downhole sensors, inclusive of accelerometers or inclinometers, capture measurements used to ascertain tool face and inclination values. These values are subsequently transmitted to the surface sensor station 14 through the rotating dipole telemetry system.

[0048] Further, a downhole turbine and generator may be added to extend the recharge the batteries, eliminating the fixed operating time limits imposed by batteries.

[0049] In a specific implementation, this invention offers three-dimensional tracking routines 28 designed to ascertain the position and orientation of the rotating magnet 12. This determination is based on data retrieved from a magnetometer 48 situated on the surface sensor station 14. Additionally the navigation and steering algorithms 30 incorporate a Kalman filter, which utilizes previous location estimations, pipe payout measurements, magnetic ranging, and dead reckoning to constrain and refine the estimated location and orientation throughout the drilling procedure. Additionally, a drill rig pipe sensor may be used to provide both pipe payout and rotation information.

[0050] As discussed above, the rotating magnet 12 is mounted just behind the bit. The rotating magnet 12 acts as a subsurface navigational beacon which produces a magnetic moment that is significantly stronger (typically 500 to 2500 A-m2) than the those produced by systems using a battery powered downhole coil and walkover detector (typically 10 to 50 A-m2). This increased strength allows for the stationary magnetometer 48 to be placed on the surface over the general vicinity of the subsurface beacon. The range between the surface sensor station 14 and the drill bit can be as large as 150 m, which eliminates the need of having an operator continually move the walkover sensor to be within range of a conventional walk-over beacon. Additionally, the issues with limited battery life and fragile downhole electronics can be eliminated.

[0051] The measurements taken by magnetometers 48 are susceptible to corruption from both ambient magnetic noise and sensor noise. Typically, these noise sources exhibit a 1 / f distribution, with higher energy at lower frequencies (f). To mitigate this, this invention provides multiple noise reduction techniques. Firstly, a Kalman filter is employed that merges dead reckoning based on the beacon's azimuth and inclination with position estimates derived from magnetic ranging. This results in a more precise estimation of the beacon's location compared to relying solely on dead reckoning or magnetic ranging. Secondly, the magnetic field produced by a rotating dipole follows an elliptical path in a plane. An analysis algorithm filters out energy that deviates from this elliptical pattern or exists out-of-plane, enhancing accuracy. Finally, the frequency band of the spinning dipole is confined either by the known rotation rate of the downhole motor or measured by the drill rig pipe sensor. This information is utilized to configure a corresponding band-pass filter, effectively eliminating out-of-band energy and further refining the accuracy of the measurements.

[0052] In one configuration, a drill rig pipe sensor package positioned near the drilling machine's spindle serves to measure both drill pipe rotation and payout. This sensor package is attached to a steel part of the drilling machine near the spindle (using magnets as one option), while another magnet is attached to the drive chuck. As the operator rotates the drive chuck, the changing magnetic field is detected by magnetometers within the sensor package. Simultaneously, a distance measuring sensor gauges the position of the drive chuck along the carriage. Distance sensor embodiments include a moving GPS receiver, a laser distance sensor, a radio range finder, or other relevant sensor technology. With these measurements, the system computes both the payout of each drill rod and the overall payout, effectively assisting in constraining the position of the downhole rotating magnet 12. Furthermore, by monitoring the rotational frequency of the drill string at the drilling machine, a band-pass filter can be applied to reduce noise in the magnetometer 48 measurements, thereby expanding the usable range between the rotating magnet 12 and the sensor.

[0053] The present invention describes several configurations for downhole rare earth magnets 12. One configuration involves arranging a row of rare earth magnets 12 on opposing sides of non-magnetic drill pipe, placed adjacent to the bit (or near the bent sub on larger rigs). The dipole moment may be aligned with the tool face of the drill string. Another configuration positions rare earth magnets 12 inside the non-magnetic pipe on a rotating mandrel. Adjacent to the mandrel, a battery-operated electronics module houses a motor for rotating the rare earth magnets 12. This module includes accelerometers (or inclinometers) to measure tool face and inclination, alongside pressure sensors to monitor internal and external drill pipe pressures. The motor's rotation creates a rotating magnetic beacon. Additionally, a data telemetry system can be established by modulating the rotation to transmit sensor data to the surface sensor station 14. A further configuration incorporates a turbine and generator to provide downhole battery charging.

[0054] In another embodiment, the present invention provides three dimensional tracking routines 28 for a rotating magnet 12, which is described herein. The magnetic field at the surface sensor station 14 produced by a subsurface rotating dipole forms an ellipse that is contained in a plane whose orientation depends on the location of the surface sensor station 14 with respect to the rotating magnet 12. The following algorithm calculates the vector range (r) between the rotating dipole and the receiver, and the axis of rotation(s) for the dipole.

[0055] If the rotational frequency of the drill string is known, apply a band-pass frequency filter to the three-component magnetometer data B measured by the base station at the surface.

[0056] Conduct a principal components analysis (PCA) using the magnetometer readings (B) to determine the principal axes bmax and bmin of the ellipse and the normal to the plane n.

[0057] Project the 3D magnetometer measurements B onto a 2D plane defined by the principal axes bmax and bmin of the ellipse. Next compute the component magnitudes Bmax and Bmin along the principal ellipse axes. One method for this uses a 2D least-squares ellipse fitting technique (Fitzgibbon et al., 1999).

[0058] Using the measurements of bmax, bmin, Bmax and Bmin, calculate the vector range (r) and axis of rotation(s) using the following relationships (Schultz et al., 2013). Due to sign ambiguities in the sine and cosine terms, there are four possible solutions for r and s. The previously estimated location is used to select the most likely solution.r·(bmaxbminn)=(cos⁢ (χ)0sin⁢ (χ))⁢ with⁢ cos⁢ (χ)=
∓2⁢13⁢(1-Bmin2Bmax2)⁢ and⁢ sin⁢ (χ)=∓13⁢(4⁢Bmin2Bmax2-1),s·(bmaxbminn)=(cos⁢ (ϕ)0sin⁢ (ϕ))⁢ with⁢ cos⁢ (ϕ)=
∓Bmax2-2⁢Bmin2Bmax-Bmin⁢ and⁢ sin⁢ (ϕ)=∓1-((Bmax2-2⁢Bmin2)2Bmax2⁢Bmin2).

[0059] In another embodiment, the present invention provides steering feedback to the drill operator with tool face and inclination measurements. These steering parameters are determined using the following algorithm.

[0060] To find the tool face from the rotating magnet (hereafter called dipole tool face), first the ambient magnetic field B0 that is not due to the rotating magnet is either calculated or measured using a low-pass filter. This is the field at the center of the ellipse plus the field normal to the elliptical plane. In the formula below, Bc,max and Bc,min are the center of the ellipse determined by the least squares fitting routine. Next the field due to the rotating magnet Br is found, which is then projected onto the bmax and bmin axes and normalized by Bmax and Bmin to obtain whitened data (i.e., points on a circle). The tool face Oy is the phase of these normalized measurements.B0=Bc,max⁢bmax+Bc,min⁢bmin+(B·n)⁢n,Bf=B-B0,Br,min=Br·bmin / Bmin,Br,max=Br·bmax / Bmaxθtf=arctan⁢ (Br,min,Br,max).

[0061] This method is designed for smaller drill rigs without downhole mud motors. Alternatively, tool face can also be measured by a downhole tilt or accelerometer sensor and the value sent to the surface using the subsurface telemetry system 26.

[0062] The inclination of the beacon can be determined from the magnetic ranging measurements through the s vector. Alternatively it can be estimated using pipe payout and the elevation differences of successive magnetic position estimates, or it can be measured by a downhole tilt or accelerometer sensors if available.

[0063] The present invention describes enhancing the location precision through the use of a Kalman filter, which dynamically predicts the location of the magnetic beacon (rotating magnet 12), and the azimuth, inclination, and tool face of the drill pipe (i.e., the state of the system). There are many Kalman filter variations (Zarchan and Musoff, 2000), and a representative example is described below. Given the initial estimated system state x0 and its uncertainty po, the subsequent predicted state of the system (xp) and its uncertainty (pp) are predicted using the following relationships:xp→=F·x0→+B·u⇀,pp→=F·p0→·Ft+Q,where F is a forecast matrix, B is a command execution matrix, u is the command, and Q is an external noise factor. The command vector contains the incremental pipe payout, as well as the azimuth, inclination, and tool face of the drill bit. This step is analogous to the dead reckoning method. Next, the beacon (rotating magnet 12) location is measured using the ranging method described above, which is then used to update the estimated system state and its uncertainty:x1→=xp→+K·(z⇀-H·xp→),p1→=p0→-K·H·R,where z is the ranging location vector, H is the sensor response function that predicts sensor readings from a given state, R is the sensor covarience, and K and the Kalman gain matrix which as calculated using p, H, and R (see Zarchan and Musoff, 2000 for details). This predict-update sequence is repeated during the drilling process so that the estimated state (including drill bit position) and its uncertainty are dynamically updated as new sensor readings become available.The methods described previously estimate the beacon location with respect to the surface sensor stations. Using the RTK GPS from the sensor station, the bit location in world coordinates is calculated and broadcast over the radio network.In another embodiment, the present invention provides a subsurface telemetry system that can send digitized sensor readings from the BHA to a surface sensor station. This method uses a motor driven magnetic dipole whose rotation rate is modulated to send data. The system uses a series of time frames (typically one second long) to send an analog data value and one bit of binary data in each frame. The analog value provides fast updates while multiple bits from successive frames are aggregated for slow but more accurate digital sensor readings.To send data, the dipole rotation velocity is modulated in a manner that can be detected by the surface sensor station. These velocity changes provide temporal framing for detecting a series of symbols and occur when the dipole rotor is at a specific angle with respect to the gravity vector. The symbols are transmitted at a constant symbol rate, fs, (i.e., one per second), with the symbol in the n″ frame coded with a changing angle θ(t),θ⁢ (t)=ωn⁢t+ϕn,where t=0 at the start of each frame. Here, @n takes one of two (or more) discrete values (ωn=2kπfs for k∈{1, 2}, k∈{−1, 1}, etc.) to represent the binary data value, and on is a scalar value (φn∈[0, 2π]) representing the analog data value. As the downhole telemetry system sends data, the surface sensor station 14 demodulates a scalar value on and a discrete value on for each symbol. For example the system might send fast analog tool face updates once per second and slow 8-bit digital pressure updates every 8 seconds.The received telemetry data is demodulated as follows. Using the measured time series values of Br,min(t) and Br,max(t), calculate the instantaneous phase θinst(t) and instantaneous frequency ωinst(t).θinst(t)=arctan⁢ (Br,min(t),Br,max(t))ωinst(i)=ddt⁢θinst(t)With a known or estimated location and rotation axis of the subsurface spinning dipole, calculate the magnetic field Bg at the surface sensor station due to a dipole rotated such that is maximally aligned with the gravity vector. Then calculate the corresponding gravity magnetic angle, θg.θg=arctan⁢ (Bg,min,Bg,max)Determine the discrete framing times tf,n where the instantaneous frequency equals its mean value, and the discrete times ton where the instantaneous phase equals the gravity magnetic angle.tf,n∋{ωinst(tf)=mean⁢ (ωinst(tf))}ntg,n∋{θinst(tg)=θg}nDetermine the fast and slow data values for each symbol:ϕn=2⁢π⁢ (tg,n-tf,n) / fskn∋ωinst(tf,n+tf / 2)=2⁢π⁢kn⁢fs,with⁢ kn∈{1,2},kn∈{-1,1},etc.The drill operator relies on frequent tool face measurements to be able to steer the drill along a planned bore path. Several methods are provided based on the size of the drill rig and the selected downhole equipment configuration. For small drill rigs without a downhole mud motor, the BHA simply contains a permanent rare earth magnet 12 that rotates with the drill string. In this case the dipole tool face can be determined using the formulas presented above. For drill rigs with a turbine and / or motor driven dipole, the tool face can be measured with an accelerometer or inclinometer and sent using the fast analog telemetry channel, and / or an accurate digital tool face value can be sent using the slow channel.The typical useful range between the downhole beacon (rare earth magnet 12) and the base station (surface sensor station 14) is on the order of 100 meters, which allows a station spacing of up to 200 meters or more. A surface sensor station 14 can be sequentially moved along the drill path as needed (typically once or twice each day), and / or multiple surface sensor stations 14 can be used for enhanced range and accuracy. Continuous updates of the downhole beacon location and orientation are sent from the base station(s) to the driller's display 16 and the steering hand's computer. Planning and guidance software on these computers provides real-time location and steering information to the driller and steering hand. All information can be sent to the cloud server 20 so that the job can be managed from a remote location. The steering hand need not be present at the job site (and can potentially manage more than one job from an office or remote location).As discussed above, the present invention describes several configurations for downhole rare earth magnets 12. According to an embodiment, FIG. 5a shows a Bottom Hole Assembly (BHA) including a series of rare earth magnets 12 in a housing 54 of non-magnetic drill pipe 50, and a drill bit 56. The rare earth magnets 12 are arranged on opposing sides of non-magnetic drill pipe 50, placed adjacent to the bit 56 (or near the bent sub on larger rigs). The dipole moment may be aligned with the tool face of the drill string or oriented at a known angle.Larger rigs utilize a hydraulic drill motor positioned just behind the drill bit, powered by pumping drilling mud through the drill string. FIG. 5b shows a Bottom Hole Assembly (BHA) including a drill pipe 50, a plurality of batteries 62, an electronic module 64, a motor 66, a series of rotating magnets (rotating rare earth magnets) 12. The annulus 74 between these components and the inside of the drill pipe allows drilling mud to pass to the hydraulic drill motor and drill bit. The bent sub 72 after the motor 66 and bit 56 is oriented (i.e., the tool face is set) to steer the drill. Adjacent to this bent sub 72 is the navigation sub that houses rotating rare earth magnets 12 and orientation sensors (i.e., accelerometers). The navigation sub operates on battery power, and an optional turbine and generator can recharge the battery 62 eliminating practical limitations in the time required for drilling completion. This is significant as some larger jobs may require weeks to complete. The rare earth magnets 12 are positioned inside the non-magnetic pipe 50 on a rotating mandrel 68, and the adjacent battery-operated electronic module 64 houses a motor 66 for rotating the magnets. The electronic module 64 includes accelerometers (or inclinometers) to measure tool face and inclination, and pressure sensors to monitor internal and external drill pipe pressures through port 58. The motor's 66 rotation creates a rotating magnetic beacon 12 that can be modulated to transmit sensor data to the surface sensor station 14.

[0076] FIG. 6 is a depiction of a drill site, according to an embodiment of the present invention. The site is comprised of a cabin 82, the surface sensor stations 14, and a drill rig 84. At least one surface sensor station 14 is needed on the job site. Typically, the surface sensor station 14 is placed about 50 meter down range of the entry point of the boring, and additional stations can be placed for enhanced accuracy and / or range to the subsurface beacon. The driller's display 16 provides real-time navigation and steering feedback to the drill operator. A computer with advanced planning and steering software may be present in the crew cabin 82. All of these components are connected by a wireless radio network that may utilize WiFi, LORA, and cellular radios.

[0077] One advantage of the present invention is that in one configuration it does not require the use of downhole electronics that can be damaged during drilling operations.

[0078] One advantage of the present invention is that in one configuration it does not require the use of downhole batteries that can become depleted before the drilling job is completed.

[0079] One advantage of the present invention is that it may alleviate the need for personnel to keep a walkover sensor in close to the bit location.

[0080] One advantage of the present invention is that it may alleviate the need for personnel to walk to various locations to determine the location of the underground beacon.

[0081] One advantage of the present invention is that it does not require deployment of large wire loops on the ground surface or large, cumbersome, heavy wire coils.

[0082] One advantage of the present invention is that an optional downhole electronics package with a motor driven rotating / spinning magnet 12 can be used to provide more accurate inclination and tool face readings, as well as optional pressure readings.

[0083] One advantage of the present invention is that it does not require the use of a wired drill pipe for telemetry, which may be unreliable.

[0084] One more advantage of the present invention is that it offers a configuration suitable for small rig HDD applications where walkover steering systems are used where drilling depth usually does not exceed a few 10s of meters and bores are typically less than 1000 feet long. The invention has an alternate configuration suitable for large drilling rigs in river crossing applications with bores approaching 5000 feet. These rigs are used to install small utility lines as well as larger pipelines with depths approaching up to 100 meters.

[0085] The foregoing description of embodiments of the 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 modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.

Claims

1. A horizontal directional drilling and guidance system for providing subsurface navigation, guidance, and steering feedback for a drill hole, the system comprising:a non-magnetic drill pipe string with integrated, electric motor driven, rotating magnets, the magnets rotate independently from the drill pipe string, the rotating magnets provide a magnetic, navigational, subsurface beacon;at least one surface sensor station sensing the presence of the subsurface beacon;a magnetometer included in the surface sensor station, the station placed over a general vicinity of the subsurface beacon; anda Kalman filter used to combine magnetic ranging and dead reckoning to provide a more accurate drill pipe string position, integrate drill rod payout, and previous location estimates together with location estimates from the subsurface beacon;whereby the magnetometer detects the subsurface beacon and provides measurements for a three-dimensional analysis to determine location and orientation of the drill pipe string.

2. The system as described in claim 1 wherein the subsurface beacon produces a magnetic moment using down hole rare earth magnets.

3. The system as described in claim 2 wherein the subsurface beacon produces the magnetic moment using the down hole rare earth magnets providing increased strength to the magnetic moment and allowing the magnetometer to be placed on the surface over a general vicinity of the subsurface beacon.

4. The system as described in claim 1 wherein a range between the surface sensor station and the subsurface beacon can be 50 to 150 meters and greater.

5. The system as described in claim 1 further including a drill rig sensor for measuring drill pipe string payout and rotation angle of the drill pipe string.

6. A horizontal directional drilling and guidance system for providing subsurface navigation, guidance, and steering feedback for a drill hole, the system comprising:a non-magnetic drill pipe string with integrated, electric motor driven, rotating magnets, the magnets rotate independently from the drill pipe string, the rotating magnets provide a magnetic, navigational, subsurface beacon;at least one surface sensor station sensing the presence of the subsurface beacon, the surface sensor station includes an embedded computer, a radio network link, an RTK GPS (real-time kinematic global positioning system) receiver system, and at least one three-component flux-gate magnetometer, the surface sensor station monitors and tracks the subsurface beacon and reports drill pipe string information over a radio network link; anda magnetometer included in the surface sensor station, the station placed over a general vicinity of the subsurface beacon, whereby the magnetometer detects the subsurface beacon and provides measurements for a three-dimensional analysis to determine location and orientation of the drill pipe string.

7. The system as described in claim 6 wherein the subsurface beacon produces a magnetic moment using down hole rare earth magnets.

8. The system as described in claim 6 wherein the subsurface beacon produces the magnetic moment using the down hole rare earth magnets providing increased strength to the magnetic moment and allowing the magnetometer to be placed on the surface over a general vicinity of the subsurface beacon.

9. The system as described in claim 6 wherein a range between the surface sensor station and the subsurface beacon can be 50 to 150 meters and greater.

10. The system as described in claim 6 further including a drill rig sensor for measuring drill pipe string payout and rotation angle of the drill pipe string.

11. The system as described in claim 6 wherein the surface sensor station includes a wireless radio network, the radio network provides data communications links between system components, the system components include a driller's display, a steering hand computer, and an optional cloud data server.

12. The system as described in claim 6 further including a subsurface telemetry system, the telemetry system is used to send data from the subsurface beacon to a surface sensor station, the telemetry system modulates the rotation rate of the motor driven rotating magnets.

13. The system as described in claim 6 wherein the subsurface beacon produces the magnetic moment typically 500 to 2500 A-m2 using down hole rare magnets providing increased strength to the magnetic moment and allowing the magnetometer to be placed on the surface over a general vicinity of the subsurface beacon.

14. The system as described in claim 6 wherein the surface sensor station includes an embedded computer, a radio network link, an RTK OPS (real-time kinematic global positioning system) receiver system, and at least one three-component flux-gate magnetometer, the surface sensor station monitors and tracks the subsurface beacon and reports drill pipe string information over the radio network link.

15. A horizontal directional drilling and guidance system for providing subsurface navigation, guidance, and steering feedback for a drill hole, the system comprising:a non-magnetic drill pipe string with integrated, electric motor driven, rotating magnets, the magnets rotate independently from the drill pipe string, the rotating magnets provide a magnetic, navigational, subsurface beacon;at least one surface sensor station sensing the presence of the subsurface beacon;a magnetometer included in the surface sensor station, the station placed over a general vicinity of the subsurface beacon; anda subsurface telemetry system, the telemetry system is used to send data from the subsurface beacon to a surface sensor station, the telemetry system modulates the rotation rate of the motor driven rotating magnets,whereby the magnetometer detects the subsurface beacon and provides measurements for a three-dimensional analysis to determine location and orientation of the drill pipe string.

16. The system as described in claim 15 further including a drill rig sensor for measuring drill pipe string payout and rotation angle of the drill pipe string.

17. The system as described in claim 15 wherein the surface sensor station includes a wireless radio network, the radio network provides data communications links between system components, the system components include a driller's display, a steering hand computer, and an optional cloud data server.

18. The system as described in claim 15 further including a subsurface telemetry system, the telemetry system is used to send data from the subsurface beacon to a surface sensor station, the telemetry system modulates the rotation rate of the motor driven rotating magnets.

19. The system as described in claim 15 wherein a range between the surface sensor stations and the subsurface beacon can be 50 to 150 meters and greater.

20. The system as described in claim 15 wherein the surface sensor station includes an embedded computer, a radio network link, an RTK OPS (real-time kinematic global positioning system) receiver system, and at least one three-component flux-gate magnetometer, the surface sensor station monitors and tracks the subsurface beacon and reports drill pipe string information over the radio network link.

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