System and method for locating and tracking a boring tool

A system for monitoring the position and orientation of a downhole tool assembly having multiple beacons. In a preferred embodiment the first and second beacons are supported by the downhole tool assembly. Both beacons are adapted to transmit signals that are indicative of the orientation and position of the downhole tool assembly. A receiving assembly detects the signals transmitted from the first and second beacons. The receiving assembly transmits the detected signals to a processor that processes the signals to produce a composite of the relative positions and orientations of the receiving assembly and the downhole tool assembly. The composite of the relative positions of the receiving assembly and the downhole tool assembly are communicated to the operator using a display. The orientations of the first and second beacons are also communicated to the operator using the display.

FIELD OF THE INVENTION

The present invention relates to an apparatus and method for drilling close tolerance horizontal underground boreholes, in particular horizontal underground boreholes requiring a close tolerance on-grade sloped or horizontal segment—such as for installation of gravity-flow storm drainage and wastewater sewer pipes. More specifically, the present invention enhances directional control during creation of the borehole.

SUMMARY OF THE INVENTION

The present invention is directed to a system for use with a horizontal directional drilling machine to monitor the position and orientation of a downhole tool assembly. The system comprises a first beacon, a second beacon, and a receiving assembly. The first beacon is supported by the downhole tool assembly and has at least one orientation sensor. The first beacon is adapted to transmit signals indicative of the position and orientation of the downhole tool assembly. The second beacon is supported by the downhole tool assembly and spatially separated from the first beacon, wherein the second beacon has at least one orientation sensor and is adapted to transmit signals indicative of the position and orientation of the downhole tool assembly. The receiving assembly comprises an antenna arrangement adapted to detect signals emanating from the first beacon and the second beacon, a processor supported by the receiving assembly, and a display adapted to visually communicate to composite of the relative positions of the receiving assembly and the downhole tool assembly and the orientation of the first beacon and of the second beacon. The processor is adapted to receive the detected signals, to process the detected signals, to generate a composite of the relative positions of the receiving assembly and the downhole tool assembly.

In another aspect the present invention is directed to a horizontal directional drilling system comprising a frame, a drill string having a first end and a second end, a rotary drive system attachable to the frame and operatively connectable to the first end of the drill string, a downhole tool assembly, and a receiving assembly. The drive system is adapted to rotate and advance the drill string. The downhole tool assembly comprises a bearing housing assembly connectable to the second end of the drill string, a first beacon supported by the bearing housing assembly for movement therewith and adapted to transmit signals indicative of the orientation of the bearing housing assembly, a front housing connectable to the bearing housing assembly and rotatable independently of the bearing housing assembly, and a second beacon assembly supported by the front housing for movement therewith and adapted to transmit signals indicative of the orientation of the front housing. The receiving assembly is adapted to monitor the orientation of the bearing housing assembly and the front housing and comprises an antenna assembly adapted to detect the signals emanating from both the first beacon and the second beacon and to transmit the detected signals, and a processor assembly adapted to receive the detected signals from the antenna assembly, to process the detected signals to determine the orientation of the front housing and the orientation of the bearing housing assembly.

In yet another aspect the present invention comprises a downhole tool assembly for use with a rotatable drill string. The assembly comprises a rotatable bearing housing assembly connectable to a second end of the rotatable drill string, a first beacon supported by the bearing housing assembly for movement therewith and adapted to transmit signals indicative of the orientation of the bearing housing assembly, a front housing connectable to the bearing housing assembly and rotatable independently of the bearing housing assembly, and a second beacon assembly supported by the front housing for movement therewith and adapted to transmit signals indicative of the orientation of the front housing.

In a further embodiment, the present invention comprises a method for drilling a borehole using a downhole tool assembly and a receiving assembly. The downhole tool assembly comprises a first beacon and a second beacon both supported by the downhole tool assembly, wherein the first beacon is adapted to transmit a first locating signal and wherein the second beacon is adapted to transmit a second locating signal. The method comprises sensing the first locating signal emanating from the first beacon and the second locating signal emanating from the second beacon, and processing the sensed first and second locating signals to generate a composite of the relative position of the receiving assembly to the first beacon and the second beacon.

In still another embodiment, the present invention comprises a method for drilling a borehole having a desired pitch using a downhole tool assembly and a signal receiving assembly. The downhole tool assembly comprises a first beacon adapted to emit a first pitch signal indicative of the pitch orientation of the first beacon and a second beacon spatially separated from the first beacon and adapted to emit a second pitch signal indicative of the pitch orientation of the second beacon. The method comprises sensing the first pitch signal and the second pitch signal using the signal receiving assembly, processing the first pitch signal and the second pitch signal substantially simultaneously to determine the pitch orientation of the first beacon and the pitch orientation of the second beacon, and comparing the pitch of the first beacon and the pitch of the second beacon to the desired pitch.

DESCRIPTION

Turning now to the drawings in general andFIG. 1in particular, there is shown therein a horizontal directional drilling (“HDD”) system10constructed in accordance with the present invention.FIG. 1illustrates the usefulness of horizontal directional drilling by demonstrating that a borehole12can be made without disturbing an above-ground structure, namely a roadway as denoted by reference numeral14. To cut or drill the borehole12, a drill string16carrying a drill bit18is rotationally driven by a rotary drive system20. When the HDD system10is used for installation of gravity-flow utilities, for example, close-tolerance or on-grade requirements are imperative. The present invention is directed to a system and method for drilling with close-tolerance and on-grade requirement.

The HDD system10of the present invention is suitable for near-horizontal subsurface placement of utility services, for example under the roadway14, building, river, or other obstacle. The HDD system10is particularly suited for drilling close-tolerance boreholes such as may be useful for the installation of on-grade gravity-flow storm drainage and wastewater sewer pipes. Close-tolerance lateral control of the borehole14, also practical with HDD system10, is advantageous in numerous applications besides gravity-flow. For instance, close-tolerance lateral control of borehole14progress can be advantageous where the available easement corridor for utility service placement is of restricted width, or when other utility services already reside within the corridor. These and other advantages associated with the present invention will become apparent from the following description of the preferred embodiments.

With continued reference toFIG. 1, the HDD system10comprises the drilling machine22operatively connected by the drill string16to a downhole tool assembly24. The HDD system10further comprises the drill bit18or other directional boring tool, the downhole transmitters or beacons26and28, and the tracking receiver30. The progression of the borehole12along a desired path is facilitated by communication of information33between the tracking receiver30and controls32for the HDD system10.

In operation, receiver30may be positioned at one of a series of reference placement stations34athrough34non the ground surface in approximate parallel alignment with the intended path of borehole12. Generally, receiver30is offset to one or the other side by the respective distances Xa through Xn. InFIG. 1, the receiver30is shown positioned at point34cand offset a distance Xc from the intended borehole12. These distances may be substantially similar, for instance within 5–10% of each other, though not required. Operation of the receiver30in conjunction with beacons26and28, as yet to be described, permits creation of a close-tolerance, on-grade borehole12.

The operation of HDD system10and the drilling machine22may be controlled manually through a system of levers, switches or similar controls at a control station36. Alternatively, operational control may be through a system that automatically operates and coordinates the various functions comprising the drilling operation. Such an automated control system is (not shown) disclosed in commonly assigned U.S. patent application Ser. No. 09/481,351, the contents of which are incorporated herein by reference. As used herein, automatic operations are intended to refer to operations that can be accomplished without operator intervention and within certain predetermined tolerances.

Referring still toFIG. 1, the drilling machine22comprises a frame38, a carriage40movably supported on the frame, a spindle42(shown inFIG. 3) rotatably supported by the carriage, and a rotary drive system20operatively connected to the spindle. In the preferred embodiment, the drill string16is connected to the spindle42by way of a threaded connection, though other ways of connecting the drill string to the drilling machine22may be used. Advancement of the carriage40by way of an axial advancement means (not shown), and operation of the rotary drive system20provide for advancement and rotation of the spindle42and, in turn, the drill string16and the directional boring tool18to create the borehole12. Reactionary forces on the drilling machine22may be resisted by machine weight supplemented by earth anchors46. As may be necessary at times, the directional boring tool18is disengaged from the earth at the distant end of borehole12by retraction of drill string16through reverse movement (to that described above) of the carriage40and rotary drive system20.

Use of the drilling machine22in a traditional manner permits the directional boring tool18to be steered or guided along a desired path Generally, the present position and angular orientation of the directional boring tool18are determined using a tracking system such as the previously mentioned beacons26,28and walkover receiver30in a manner yet to be described. That information may be compared to the pre-planned desired path for the borehole12to determine whether a steering correction is necessary. If a steering correction is not needed, the directional boring tool18is advanced in a straight line by advancing and rotating the drill string16. If a steering correction is required, the directional boring tool18is rotated to a proper heading (i.e., roll position). Change the direction of the borehole12. The drill string16is then thrust forward by advancing carriage40without rotation by the rotary drive20. The directional boring tool18deflects off its previous course heading as the tool engages virgin soil beyond the point where rotational advance ceased. Steering response can be diminished—as may be necessary for example while drilling a curved section of the planned borepath—by periodically interjecting short “straight” (advance with rotation) drilling segments.

As used herein, directional boring tool18may be any drilling device or drill bit which may cause deviation of the tool from a straight path when thrust forward without rotation, or if thrust forward while being repetitively rocked through an arc of partial rotation as disclosed in U.S. Pat. No. 6,109,371 issued to Kinnan, incorporated herein by reference or by other know methods. Directional boring tools suitable for use with the present invention include those described in U.S. Pat. No. 5,799,740, issued to Stephenson, et al., the contents of which are incorporated herein by reference, as well as carbide studded cobble drilling bits and replaceable tooth rock drilling bits.

The horizontal directional drilling system10depicted inFIG. 1and of the present invention may be used with either a dual-member or a single-member drill string Specifically, in accordance with a first downhole tool assembly48embodiment of the present invention (shown inFIG. 4and yet to be described) drill string16comprises a dual-member drill string. Alternatively, of downhole tool assembly50(shown inFIG. 6and yet to be described), the drill string16comprises a single-member drill string. The drill string16may be continuous, or comprise the assembly of a plurality of pipe sections (a.k.a. pipe joints).

Turning now toFIG. 2, there is shown one of a plurality of dual-member pipe sections52comprising the dual-member drill string16. The dual-member pipe section52comprises an outer member54and an inner member56. Outer members54and inner member56of adjacent pipe sections,52are connected to form the dual-member drill string16a(FIG. 4). Interconnected inner members56of adjacent dual-member pipe sections52are rotatable independently of the interconnected outer members54. An annular space58between the inner members56and outer members54, or a hollow tubular construction for inner member56(not illustrated), may be useful for conveyance of drilling fluid downhole for purposes later described. One or the other of these longitudinal cavities may also be useful for conveyance of slurried drill cuttings uphole for disposal. It will be appreciated that any dual-member drill string having an outer member and an inner member, the inner member disposed within the outer member and independently rotatable, may be used with the present invention. Embodiments for suitable dual member drill strings are described in U.S. Pat. No. 5,490,569 and U.S. Pat. No. 5,682,956, the contents of which are incorporated herein by reference.

Turning now toFIG. 3, a dual rotary drive system44is shown for use as the rotary drive system20(FIG. 1). The rotary drive system44has dual-spindles42for driving a dual-member drill string16a. Rotary drive system44is slidably mounted on the frame38of drilling machine22(FIG. 1) by way of the carriage40. The rotary drive system44comprises two independent drive groups62and64for independently driving the respective interconnected outer members54and interconnected inner members56comprising the dual-member drill string16a. The outer members54and inner members54are thereby independently controllable of each other. For instance, as is advantageous with the present invention, outer members54can be held without rotation while inner members56are rotated. A suitable dual-spindle rotary drive system44is disclosed in U.S. Pat. No. 5,682,956, which is incorporated herein by reference. As subsequently described, inner member drive group62, also called the inner member drive shaft group, may be adapted to rotationally drive directional boring tool18.

With reference now toFIG. 4, shown therein is the downhole tool assembly48used with a dual-member drill string16ato create borehole12. Downhole tool assembly48comprises the two on-board transmitters or beacons26and28. Data or information transmitted by the beacons26and28is received and processed, in a manner yet to be described, by receiver30. Information processed by the receiver30may be relayed by wireless communications link65to the drilling machine22, for determining, for example, if a steering correction is required. Alternately, use of the processed information may be accomplished within tracking receiver30and control signals33communicated to the drilling machine22.

FIG. 5shows the downhole tool assembly48ofFIG. 4in cross-sectional detail. For illustration proposes, side-entry chambers66and68shown at the 9 o'clock roll angle orientation inFIG. 4have been moved to the 12 o'clock orientation inFIG. 5. In reference the downhole tool assembly48has a forward portion70comprising a forward housing assembly72and a rear portion74comprising a bearing housing assembly76. The forward housing assembly72is preferably fixedly attached to the drill string16a. The round cross-section “forward” and “rearward” portions of downhole tool assembly48—excluding the slant-faced drill bit—may have a substantially uniform diameter, as so depicted. It should be understood, however, that equality of diameter between the forward and rearward portions of tool48is not required.

The directional boring tool18is represented herein by the flat-faced bit and a fluid dispensing nozzle. However, as previously mentioned, directional boring tool18may be any drilling device or bit which causes deviation of the tool from a straight path when thrust forward without rotation, or if thrust forward while repetitively rocking the drilling bit or boring tool through an arc of partial rotation. The bit, mounted at an approximated 10-degree angle on the downhole end of forward housing assembly72, is rotationally fixed to the inner member56of the drill string16aby way of inner drive member116(indicated inFIG. 4by its front portion). Thus the rotation of these components is through the control of inner member drive group62.

Forward housing assembly72comprises the side-entry chamber66to accept the front transmitter or beacon26, held therein by slotted retaining cover78. It should be noted that housing assembly72could be configured for front-loading or end-loading of the front beacon26. Preferably, the front beacon26is held in rotationally indexed relation to the orientation of directional boring tool18such that a roll sensor (not shown) disposed in the front beacon may correctly indicate the rotational orientation of directional boring tool18. It will be appreciated that the front beacon26may contain other sensors as deemed appropriate.

One can appreciate that other methods may also be utilized to indicate the roll position of the directional boring tool18. For example, a relative rotational position indicator (not shown) within the bearing housing assembly76could indicate the roll orientation of forward housing72and directional boring tool18relative to the absolute rotational position of the bearing housing. The relative rotational position indicator could transfer information to the beacon28for communication to receiver30. Thus, the forward beacon26would not be required for this purpose, requiring fewer electronics in the forward beacon and allowing length reduction of the forward housing assembly72. The resultant reduction in length and surface area of the assembly72can be advantageous in high friction soil conditions where the torque transmitting capability of inner member56of drill string16amay be limiting.

With continued reference toFIGS. 4 & 5, the bearing housing assembly76comprises the inner drive member116bearingly supported within a housing80. The housing80comprises the side entry chamber68. The rear beacon28is positioned in the chamber68and held therein by a slotted retaining cover81. The housing80further comprises an outer wall82that defines an interior bearing chamber84. A rear end of the housing80is connectable to the outer member54of the drill string16a. Preferably, the housing80has male threading85for connection to a threaded female receiving connection86on the outer member54of the drill string16a. However, it should be understood that other torque transferring connections and configurations for the connections between the housing80and the drill string16aare contemplated.

The bearingly supported inner drive member116has a rear portion88, a body90, and a front portion92. The front portion92is operatively connectable to the previously described forward housing assembly72. In the preferred embodiment, the front portion92comprises a female threaded connection93for connection to a corresponding male threading95on the forward housing72. The rear portion88extends out from the housing80and is connectable to the inner member56at the downhole end of the drill string16asuch that torque of the inner member is transferred to the inner drive member116. Preferably, the rear portion88of drive member116comprises a geometrically shaped female connection94for sliding connection to a similarly shaped male connection on the inner member56of the drill string16a. Other torque transferring connections and configurations for the connections between the inner drive member116and the drill string16aare also contemplated.

The body90of the inner drive member116is supported within the bearing chamber84of the housing80by a bearing arrangement96. Preferably, the bearings96are sealed and position the inner drive member116generally coaxially within the housing80. However, some lateral offset or non-symmetrical outer diameter for housing80is permissible to accommodate beacon28therein. In the preferred embodiment, seals98, wear rings100, and seal gland102are positioned to retain the bearings96in position around the body90. Preferably, the sealed bearings96are periodically lubricated via a pluggable point of access (not shown). This arrangement prevents slurried drill cuttings from reaching and damaging the bearings96.

One skilled in the art will appreciate the use of drilling fluids during horizontal directional drilling for purposes such as cooling the directional boring tool18and the beacons26and28, and to stabilize the borehole. Preferably, the inner drive member116comprises at least one fluid passage104for communicating drilling fluid from the annular space58(shown inFIG. 2) between the inner member56and the outer member54of the drill string16athrough the downhole tool assembly48for discharge through a nozzle106at a front end of the forward housing assembly72. The fluid passage104preferably passes in proximity to beacons26and28prior to reaching nozzle106.

With reference toFIGS. 4 and 5, directional boring tool18and forward housing assembly72are rotatable by the inner member56of the dual-member drill string16aindependently of the bearing housing assembly76, the latter being held without rotation or being separately rotatable by the outer member54of the dual-member drill string. As the inner member56of the drill string16ais rotated, the change in rotational orientation of the boring tool18can be detected by the roll sensor of front beacon26. This information may be transmitted to the above-ground tracking receiver30, where it can be further processed, displayed to the receiver operator, and relayed by wireless communications link65or other means to the operator and/or automated control system of the drilling machine22.

With reference now toFIGS. 6 and 7, shown therein is a downhole tool assembly50for use with a single-member drill string16b. The downhole tool assembly50comprises a forward housing assembly108and is substantially identical to that of the assembly72in the previously described embodiment ofFIGS. 4 and 5. Similarly as in that embodiment, a side-entry chamber110—shown in 9 o'clock roll angle orientation in FIG.6—has been moved to the 12 o'clock orientation inFIG. 7. The downhole tool assembly50further comprises a bearing housing assembly112at a rear portion of the tool assembly. The bearing housing assembly112is adapted for attachment to the downhole end of the single-member drill string16b.

The bearing housing assembly112, shown in greater detail inFIG. 7, comprises a bearing housing114with a straight central axis and an inner drive member116. The inner drive member116is bearingly supported and passes through bearing housing114.

The inner drive member116has a rear portion118, a body120, and a front portion122. Preferably, the inner drive member116comprises at least one fluid passage124for communicating drilling fluid from the interior of single-member drill string16bthrough the downhole tool assembly50for discharge through a nozzle126at a front end of the forward housing assembly108. The front portion122of the inner drive member116is operatively connectable to the forward housing assembly108. Although other forms of construction are contemplated, in the preferred embodiment the front portion122comprises a female threaded connection. The inner drive member116is connectable to the downhole end of the single-member drill string16b.

As shown inFIG. 7, the bearing housing assembly112is held in axial assembly by roll pin128engaging the body portion120of inner drive member116to the rear portion118. Mating splines (not shown) are contemplated for torque transferal between the body portion120of inner drive member116and rear portion118of the inner drive member116.

Continuing with reference toFIGS. 6 and 7, the inner drive member116of bearing housing assembly112is supported within the bearing housing114by bearings130. The rear portion118of inner drive member116extends out from the housing114and is connectable in threaded engagement to the downhole end of drill string16bfor torque and thrust transferal. Although threaded engagement is preferred, other torque transferring connections and configurations for the connections between the various components are contemplated. Thus, whenever the single-member drill string16bis rotated, the interconnecting inner drive member116rotates the forward housing assembly108and the directional boring tool18. The inner drive member116is bearingly supported to prevent corresponding rotation of housing114.

Bearing housing114defines an outer wall132and an interior bearing chamber134. The body120of the inner drive member116is supported within the bearing chamber134by bearing arrangement130. Preferably, bearings130are sealed and position the inner drive member116generally coaxially within the housing114. However, some lateral offset or non-symmetrical outer diameter for housing114is permissible to accommodate the beacon28therein. In the preferred embodiment, seals138, wear rings (not shown), seal glands140, and thrust washers142are positioned to retain the bearings130in position within housing114and around the body120of inner drive member116. Preferably, the sealed bearings136are periodically lubricated via a pluggable point of access (not shown). This arrangement prevents slurried drill cuttings from reaching and damaging the bearings136.

Bearing housing114may further comprise an exterior structure for engagement with the wall of the borehole12to prevent rotation of the housing114. Frictional contact forces, spring-loaded fins, or a variety of other techniques may be utilized for this purpose. For instance, bearing-mounted rolling cutter stabilizers144, shown inFIG. 8, built into housing114may serve this purpose. Alternatively, there is shown inFIG. 9a cross-sectional view of an alternative bearing housing114awherein the outside diameter is constructed to be an interference fit in the borehole12. Exterior scallops146reduce the effort required to thrust the stabilized housing114aalong borehole12. The scalloped minor outside diameter of housing114amay be sufficiently undersized of the borehole12to allow slurried drill cuttings to flow past the housing.

Returning toFIGS. 6 and 7, bearing housing114comprises a side-entry chamber147to the accept rear transmitter or beacon28, held therein by a slotted retaining cover148. As with the embodiment shown inFIGS. 4 and 5, certain sensors within the beacon28may have a preferential roll angle alignment, or it may be desirable to hold the sensors in a substantially constant roll angle alignment for improved accuracy of measurement. One skilled in the art will appreciate the need for the ability to index the bearing housing114properly after entry into the borehole12. This may be accomplished by including a dog clutch (not shown) or similar push-pull locking device within housing assembly112—as described in U.S. Pat. No. 5,490,569 issued to Brotherton, et. al., the contents of which are incorporated herein by reference. Such a device, engaged by retracting the drill string16b, temporarily rotationally locks inner drive member116to the bearing housing114wherein rear beacon28can be indexed to its preferred roll angle alignment. Disengagement is then accomplished by thrusting drill string16bforward without rotation. Other clutching devices may also be suitable for this purpose, such as those engaged by reverse rotation of drill string16b, an increase in drilling fluid pressure, or diversion of drilling fluid flow.

With reference to the embodiments ofFIGS. 6–9, to drill a straight segment of borehole12, the directional boring tool18is advanced while rotated by the single-member drill string16b. To change direction, the directional boring tool18is oriented in the desired direction by aid of the roll sensor in front beacon26, then advanced without rotation of drill string16b. In either case, bearing housing114is advanced without rotation because of its interfering contact with the borehole12. By virtue of its contact with the wall of the borehole12, the bearing housing114serves as a stabilizer for the forward portion of downhole tool assembly50, enhancing its ability to drill a close-tolerance horizontal segment of the borehole12.

The position and orientation sensing system comprised of beacons26and28and walkover receiver30(FIG. 1) will now be described in greater detail. From the embodiment descriptions herein, it should be apparent that whenever the directional boring tool18is rotated to drill a straight segment of the borehole12, the front beacon26and sensors therein for measuring one or more of the angular orientations of forward housing assemblies72and108also rotate. Rotation can detrimentally affect pitch sensor readings, which are critical for on-grade applications. Also, yaw orientational outputs are generally unavailable at drilling rotational speeds. Placement of such sensors in a non-rotating rear beacon28of the present invention overcomes the need for the rotational advance of directional boring tool18to be stopped frequently to verify that it has not been deviated up-down and/or left-right off a straight path line by such effects as gravity, the tendency of a rotating bit to “walk”, or variations in soil conditions. The monitoring of pitch and, if so desired, yaw headings throughout the creation of the borehole12offers substantial productivity improvement. Constancy of the pitch and yaw angular heading components gives assurance that a straight path is being maintained, within the constraints of sensor measurement system accuracy.

For the embodiments ofFIGS. 4–9, as indicated previously, beacons26and28may comprise one or more sensors for measuring information representative of one or more of three angular orientations: roll, pitch and yaw of the respective forward and rearward portions of downhole tool assemblies48or50. Specifically, the front beacon26may sense at least the roll orientation angle of directional boring tool18. The rear beacon28can sense at least the pitch orientation angle of the rearward portion of the downhole tool assemblies48or50and, as may be desired, also its yaw orientation. It should be understood, however, that this does not preclude inclusion of a roll sensor in rear beacon28—as may be required to properly orient some types of yaw sensors. Additional sensors may also be included within beacons26and28. Sensors for orientation determination may comprise a variety of devices, including: inclinometers, accelerometers, and gyroscopes. This information is attached onto the respective signals transmitted by the beacons26and28to the above-ground tracking receiver30by means of various known communication schemes. Beacons26and28and the tracking receiver30preferably constitute an improved, yet to be described position and orientation sensing system. However, a basic walkover style position and orientation sensing system could also be utilized. Such systems are described in U.S. Pat. No. 5,264,795 issued to Rider, U.S. Pat. No. 5,850,624 issued to Gard, et. al., and U.S. Pat. No. 5,880,680 issued to Wisehart, et. al., the contents of which are incorporated herein by reference. Orientation sensors for determining the roll (a.k.a. tool face), pitch (a.k.a. inclination and grade), and/or yaw (a.k.a. left-right heading and azimuth) angular coordinates comprising the vector heading of the drill head are described in the latter two patents as well as in U.S. Pat. Nos. 5,133,417 and 5,174,033 issued to Rider and U.S. Pat. No. 5,703,484 issued to Bieberdorf, et. al., the contents of which are also incorporated herein by reference.

As used herein, it should be understood that the sensors of beacons26and28provide the above-mentioned angular information with sufficient accuracy for drilling close-tolerance boreholes. As with front beacon26and its housing72or108, the rear beacon28is held in rotationally indexed relation to the orientation of housing80or114to insure there is no shift in rotational relationship during drilling. Preferably, beacons26and28and their internal sensors are maintained in parallel axial alignment with respect to the central axis of downhole tool assemblies48or50. Not withstanding that preference, one skilled in the art can appreciate that residual non-parallelism can be removed through system calibration and electronic compensation after placement in their respective chambers. It can also be appreciated that, although not so depicted inFIGS. 4–9, some radial protrusion of chambers66,68and110and slotted covers78,81and148will not detrimentally detract from the performance of downhole tool assemblies48or50.

One skilled in the art will appreciate that other types of position and orientation sensing systems—such as “remote” (non walkover) systems—would also be suitable for use with one or more drilling systems described herein. Alternately, a wireline or other drill string communication system could carry certain information from beacons26and28back to the drilling machine22instead of the wireless communications link65illustrated inFIGS. 1 and 4.

The frequency transmissions of beacons26and28will now be considered. The signal transmissions of conventional beacons are generally at a fixed frequency of either 29 kHz or 33 kHz. Two HDD systems10can successfully drill adjacently if their respective beacons26and28transmit and their respective walkover tracking receivers30are set up to receive one or the other of these distinct frequencies. In the present invention, the requirements are that the chosen frequencies be within the range of beacon frequencies suitable for HDD applications, and that their transmissions be sufficiently distinct. Frequency separation and/or improved filtering are techniques for minimizing cross-talk. Beacons26and28may be positioned in close proximity (less than 10 feet of separation) and transmit to one tracking receiver30. In this arrangement, two frequencies within an approximate 8 kHz to 40 kHz range may be suitably distinct to prevent undo cross-talk between respective spatially separated transmitting antennas when their frequency separation is on the order of 4 kHz to 10 kHz. For example, the frequencies of 25 kHz and 29 kHz are suitably distinct without improved filtering. Although not required, the lower of the two frequencies may be assigned to forward beacon26.

When a 25 kHz signal is transmitted by front beacon26and a 29 kHz signal is emitted by rear beacon28, both signals may be processed by tracking receiver30to determine the position of downhole tool assembly48or50. Sensor information conveyed on these respective signals may also be decoded by tracking receiver30to obtain the respective angular orientations of directional boring tool18(being the same as forward housing assembly72or108) and housing80or114.

Whenever progress of directional boring tool18is paused, for instance when another pipe section52must be added to extend drill string16, the location (x,z) and depth (y) of one or both beacons26and28can readily be ascertained in a known manner by use of a conventional walkover receiver having selectable frequency reception, or preferably by tracking receiver30. The employment of tracking receiver30allows both position and orientation information to be obtained whether or not drilling is underway. It is advantageous that this information can be determined in a measurement-while-drilling (MWD) manner throughout the progress of creating the borehole12; e.g., between any necessary pauses to add pipe to drill string16. It will be appreciated, however, that a continuous drill string may be used instead of a segmented drill string.

As stated earlier, rear beacon28of the present invention is held without rotation by outer drill string member54or, for the single-member drill string embodiments, by the stabilizing features144or146of housing114or114a. This offers substantial productivity improvement by allowing pitch—and, when the sensor is included, yaw—headings to be monitored throughout the creation of the borehole12. This is particularly advantageous while drilling a straight path segment of the borehole12wherein to maintain the present heading, forward housing assembly72or108is rotated while carriage40is advanced. Thus any heading sensors within front beacon26are subjected to the previously described effects of rotation, whereas those in rear beacon28are not. Tracking receiver30may now utilize the signal transmissions of rear beacon28to process, display, and relay heading and/or positional information for MWD determination whether or not a straight path is being maintained. This enables “on the fly” decision-making control of the HDD system10by its operator or by its automated control system.

If a pitch sensor is included within front beacon26, tracking receiver30may receive the pitch of the forward housing assembly72or108as well as the pitch of bearing housing assembly76or112. The comparison of these spatially separated pitch readings may be possible whenever the directional boring tool18is being advanced without rotation to correct or change the directional slope (pitch) of the borehole12. This is particularly advantageous for close-tolerance on-grade installations.

When directional boring tool18such as a flat blade bit is thrust forward without rotation, the soil applies a force component perpendicular to the central axis of downhole tool assembly48or50that highly influences the resulting directional change. This perpendicular force component generates a curvature within downhole tool assembly48or50and, generally, also within a short adjacent portion of drill string16extending uphole. Thus a change in this “steering force” component can be ascertained by monitored comparison of pitch sensor data transmissions from spatially separated beacons26and28. Also, once advance without rotation is initiated, the onset of a dynamic differential between the two pitch readings gives early indication that an up-down directional change is being effected.

Turning now toFIG. 10, shown therein is a tracking receiver30having the ability to monitor the position and orientation of the beacons26and28within the operating area of the HDD system10. Positional information (i.e., location and depth) along with pitch heading (and yaw, if desired) is manually or automatically compared to the desired path for the borehole12, thereby determining any need of directional change in the next interval to be drilled. In general, receiver30may be comprised of a plurality of magnetic field sensors150an152, appropriate electronics (not shown) for the amplification and filtering for the outputs of each magnetic field sensor, a multiplexer (not shown), an A/D converter (not shown), processor (not shown), a display154, wireless communications link65, batteries (not shown), software/firmware, and other items necessary for system operation, as well as useful accessories (not shown) such as a geographical positioning system.

The throughput of the multiplexer and A/D converter may be designed sufficiently high that the digital representations of the magnetic field vector components sensed by the plurality of magnetic field sensors150and152are satisfactorily equivalent to being measured at the same instant of time.

The processor within tracking receiver30may utilize the magnetic field information and reference positional data (to include the present location of tracking receiver; i.e., the previously described reference placement stations34) to produce a composite list of information indicative of the relative positions of the beacons with respect to the receiver and the desired path of the borehole12. This information can be transferred to the display154(better seen inFIG. 11) of receiver30and communicated by antenna156to the drilling machine22for control of the HDD system10.

The placement of receiver30must be within an area where reception of the magnetic fields emanating from beacons26and28are sufficiently distinct for detection, amplification, filtering and processing into positional information having the desired level of accuracy. Further, for ease of handling boundary conditions and positive-negative sign conventions within the software algorithms, it may be advantageous to position receiver30forward of the progressing downhole tool assembly48or50and always in a given approximate orientation thereto. For instance, as illustrated inFIG. 1, it may be advantageous to face receiver30toward the approaching downhole tool assembly and align it approximately parallel to the desired path of the borehole12when placed on the ground surface at one or more reference placement stations34athrough34nestablished along that desired path. It may be further advantageous that these reference stations be laterally offset from the desired path approximately 5–10 feet, for improved resolution of the magnetic field components emanating from the two beacons. Whenever the advancing downhole tool assembly reaches its locale, the receiver30may be repositioned at the next adjacent reference station. The station spacing may be limited by the above-mentioned reception range, thus the intended depth of the borehole12can be a factor in their spacing. One can appreciate that other relational alignments may be advantageous toward simplification of the software algorithms and/or hardware of tracking receiver30.

Before continuing the description of tracking receiver30, it will be useful to define one or more coordinate systems and reference points or planes. As used herein, the coordinate “z” may represent horizontal distance along the general heading of the borehole12, the coordinate “x” may represent the left-right horizontal position relative to a particular reference line, and the coordinate “y” may be the depth below ground surface or the vertical offset from a horizontal reference plane. A temporary or local benchmark may serve as the base reference point. A useful temporary benchmark may be the ground entry point of directional boring tool18, which may be considered as the global origin (x=0, y=0, z=0). It may also be useful to pre-establish secondary origins nearby and along the intended course for the borehole12coinciding with the reference stations34athrough34n(FIG. 1).

With continuing reference toFIG. 10, the plurality of magnetic field sensors150and152detect the vector components Hx, Hy and Hz of the composite of the respective magnetic fields and other signals emanating from the beacons26and28. The magnetic field sensors preferably form two antenna arrays150and152separated by a known distance L. For purposes of illustration, antenna arrays150and152are shown in a top and bottom arrangement. Antenna arrays150and152comprise three antennas150x,150y,150z, and152x,152y, and152z, respectively, oriented such that each antenna of each array is mutually orthogonal to the other two. Arranging the antennas in this manner allows the tracking receiver30to measure the composite magnetic field components emanating at distinct frequencies from the beacons26and28in three planes. The measured magnetic field components are separated by the processor into the distinct vector components of each beacon frequency through the utilization of DSP filters and detectors (not shown). Such an arrangement allows determination of the respective beacon positions and also reception of their orientational sensor information without receiver30being directly overhead.

Since there are two antenna arrays150and152, there are two sets of magnetic field components resolved at two spatially separated points (separated by the vertical distance L) in the emitted fields of each beacon. Were the placement of tracking receiver30always in a known and repeated manner, for instance in the position and orientation described earlier, the two sets of respectively resolved magnetic field vector components emanating from beacons26and28may be more readily utilized to calculate their respective position and depth in relationship to the two antenna arrays150and152. These relational distances may be translated to coordinates based from the secondary origin at the presently occupied reference station34c(FIG. 1), and thence transformed into global coordinates. The location coordinates of the two beacons define two points in three-dimensional space that may be used to estimate the “average” pitch and yaw of downhole tool assembly48or50. The two sets of magnetic field components may also be used to estimate the respective pitch and yaw of beacons26and28. Sequential comparisons and beacon-to-beacon comparison of these estimates may be useful preliminary indicators of change in the heading of the borehole12. However for on-grade applications in particular, “field component” pitch estimates are unlikely to yield sufficient accuracy to supplant the need of a pitch sensor in one or more of the beacons.

A vector summation of each set of the resolved magnetic field vector components for each beacon separately determines their respective total fields TopFand BotF, and TopRand BotRsensed by antenna array150and152respectively. (“F” represents front beacon26, “R” represents rear beacon28, “Top” represents the upper antenna array152, and “Bot” represents the lower antenna array152.) The direction angles from each antenna array150and152to each beacon26and28may be determined by ratioing each total field to its resolved magnetic field vector components. The distances between each antenna array and each beacon can be determined from these sets of angles and the known distance L by utilizing the law of cosines. These “straight line” distances may then be converted to the above-mentioned position (X, Z) and depth (Y) components. Non parallel alignment between the actual position of downhole tool assembly48or50and the placement of tracking receiver30may also be determined from the measured magnetic field components, for visualization on the display154.

It should be clear from the above discussion that, in addition to pitch and azimuthal information, positional and depth of beacons26and28can be determined while the downhole tool assembly48or50is being advanced with or without rotation in the creation of borehole12.

Turning now toFIG. 11, shown therein is the display154of tracking receiver30. The display154gives the operator a clear, easy-to-read display of the area through which the downhole tool assembly48or50and beacons26and28are moving. The controls comprising five keys160are positioned for convenient one-handed operation, and control all the functions of the tracking receiver30.

The display154is capable of providing the tracking receiver operator with a wide array of information related to the horizontal directional drilling operation. Such information may also be relayed to the operator of drilling machine22in a manner previously described, whether or not tracking receiver30is being monitored by its operator. In other words, the tracking receiver operator need not remain in the vicinity of receiver30other than to periodically advance it to the next reference placement station. As shown inFIG. 11, a liquid crystal display (“LCD”) may be used to display several operating parameters of the boring operation in addition to the positional relationship of the beacons26and28with respect to tracking receiver30. For example, the operator may monitor the roll orientation of the beacon26, and the pitch and/or azimuthal information of beacon28. Depth (y), lateral offset (x) and radial distance to one or both beacons can also be displayed with respect to the presently occupied reference station34c, the radial “ray” relationship being indicated by broken lines162and164.

The display154may be configured to use either textual characters or icons to display information to the operator. For example, graphical display166displays roll orientation of the beacon26while textual displays168and170display the respective pitch of beacon26and28. These segments of display154may be shifted—by scrolling to other menu selections accessible via keys160—to display the positional coordinates of beacon26and/or beacon28with respect to tracking receiver30or to display azimuthal information that may be available from one or more of the beacons. Other information icons (not shown), such as temperature and battery strength of the beacons can be programmed to appear upon operator request or when one or more operating parameters reach a critical range.

Display154is adapted to show a composite display of the operating area. The composite shows the relative positions of the beacons26and28, and the tracking receiver30. The receiver30is represented by a receiver icon172. The beacons26and28in downhole tool assembly48or50are represented on the display154by a downhole tool assembly icon174. Numerical displays (not shown) may be used, in conjunction with broken lines162and164, to communicate the horizontal distance, depth, and angle of orientation of the beacons26and28relative to the tracking receiver30.

The receiver icon172remains in a fixed position on the display154during operation of the system while the positional relationship between the downhole tool assembly icon174changes with respect thereto to reflect progress of the boring operation. The downhole tool assembly icon174also shows azimuthal orientation relative to the receiver icon172as azimuth of the downhole tool assembly48or50changes in relation to the tracking receiver30. In other words, the “parallel heading” of icon174with respect to receiver icon172illustrated on display154inFIG. 11can be varied to reflect the actual measured orientational relationship of downhole tool assembly48or50and tracking receiver30.

Continuing withFIG. 11, the five keys160function to provide a user-friendly interface between the tracking receiver30and its operator. The menu key160ebrings up the menu screen, and is also used to revive the system after it has entered sleep mode. The left and right arrow keys160aand160care used to adjust various system operating parameters as needed. The up-arrow key160band the down-arrow key160dare used to step through selections within functions, and to raise and lower adjustments such as sensor assembly gain. Keys160are not limited by this description, and may be programmed for other useful functions and operations.

As stated previously, “remote” (non walkover) systems could be utilized to obtain the above-described positional and orientational information. For instance, sensor information from forward housing assembly72or108could be communicated by short distance electromagnetic telemetry to housing assembly76(or oppositely in the instance of housing assembly112) wherein resides essentially a conventional remote navigational system (a.k.a. an electronic “steering tool”) which relays the information of both forward and rear sensor packages up drill string16by one of several known techniques.

Turning now toFIG. 12, shown therein is a basic flow chart for employing pitch readings of two spatially separated beacons26and28toward the aid of making steering decisions. Those skilled in the art of horizontal directional drilling appreciate that a number of different indicators can be utilized to verify whether or not directional boring tool18is progressing the borehole12along its desired course. Sometimes singular indicators are sufficient, but most often the combination of several are utilized. For instance, determination of the need for an up or down (12 o'clock or 6 o'clock) steering correction could be substantiated by or even solely determined by measuring the depth of front beacon26, rear beacon28, or both, with tracking receiver30and relating this information to a reference surface elevation for comparison to the desired course. A step-wise pitch calculated from the above depth readings could also be used to infer proper course heading. Appropriate decision logic of this nature could be incorporated at steps402and404ofFIG. 12.

With continuing reference toFIG. 12, the “advance with rotation” operating mode400entry point into the flow chart represents a directional boring tool18that is drilling the on-grade “horizontal” section of the borehole12. Boring tool18is advanced with rotation to continue progressing on its present heading. However, in the manner previously described, boring tool18may begin drifting off course. This is detected in step402by comparing the MWD pitch readings of rear beacon28(Pitch2or P2) to the “Desired Pitch” (DP). This comparison may be either time interval or distance interval based. In step404, if P2equals or is within a preselected tolerance of DP, advance with rotation continues at step400. If P2is greater than DP (i.e., P2−DP>0) by more than the preselected tolerance, advance with rotation ceases and directional boring tool18is oriented to the 6 o'clock position at step406. In the opposite case, where P2is less than DP (i.e., P2−DP<0) by more than the preselected tolerance, advance with rotation ceases and directional boring tool18is oriented to the 12 o'clock position at step408. This preselected tolerance and other preselected parameters within theFIG. 12flow chart may be initially set on the basis of anticipated soil conditions along the desired course of borehole12. As will soon be described, some or all of these parameters may be incrementally adjusted as the bore progresses, to reflect the recently noted responsiveness of directional boring tool18.

A correction back on-grade is initiated at step410. The initialization process at step412involves a first comparison of P1, the pitch of front beacon26, with P2to adjust for any residual or quasi-static differential. It may also be useful at this time to “normalize” P1and P2through their division by DP (or alternately by subtraction of DP from their values). This normalized “Current Pitch” (CP) then becomes the reference pitch from which changes are measured while the boring tool18is advanced beyond this point without rotation.

In the feedback loop of steps414,416and418, directional boring tool18is advanced without rotation until the absolute value of P1minus CP plus the absolute value of P2minus CP exceeds a preselected value indicative that a potentially sufficient up/down directional change has been initiated. Absolute values are summed at step416since the previously mentioned steering-induced curvature to downhole tool assembly48or50may cause, in the instance of a 12 o'clock (6 o'clock) steering direction, a decrease (increase) in P2of approximately the same angular amount that P1increases (decreases) in response to the steering force. In such an instance, direct addition (P1+P2) would incorrectly suggest that a steering correction had yet to be initiated. The preselected “Set Amount” in step416must also accommodate sensor and measuring system resolution. If, for example, the pitch sensors of beacons26and28—in combination with the circuitry of the beacons and receiver30—are capable of resolving a change in grade no smaller than 0.1%, the preselected comparison value (i.e., the initial “Set Amount”) in step416could not be that small (i.e., 0.1% slope) but more preferably on the order of 0.2% slope. In subsequent passes through this loop, adjustments may be made, at step412, to the preset parameters of step414or to the form of logic and/or its preselected tolerance at step416.

The sufficiency of the above directional change to bring borehole12back onto the desired grade or pitch, DP, is tested beginning at step420by advancing a preset distance while the boring tool18is being rotated. In average soil conditions this distance is preferably preset at approximately 12 inches. Advance and rotation are stopped at step422, then rotation is indexed to the prior 6 or 12 o'clock steering direction utilized at step410. Since some offset may have been introduced through the actions of steps414through422, the average of P1and P2are compared to DP at step424. Alternatively, P1alone could be compared to DP at this point. If the comparison is favorable, as indicated by a zero or within preselected tolerance differential, borehole12is back on the proper grade and advance with rotation continues at step400. If the necessary correction is yet to be achieved, preset parameters may be incrementally adjusted upon return to step412.

In the event over-correction has occurred, it must be counteracted by a short segment of steering in the opposite direction. This is indicated inFIG. 12by returning to step402. Alternately, since the prior 6 or 12 o'clock steering direction is known, boring tool18could be indexed to the opposite orientation and control returned directly to step410. In either case, appropriate preset parameters would be adjusted to factor in the recently noted steering response of directional boring tool18before initiating this short steering segment. In this or other subsequent passes through the overall control loop, adjustments may be made to the preset parameters of steps402,414,420, and422or to the form of logic and/or its preselected tolerance at steps404,416, and424.

Other control logic is contemplated for utilizing the pitch of multiple spatially separated beacons. Multiple beacons offer improved manual and/or automatic operation of the HDD system10, particularly when drilling the close-tolerance on-grade segment of the borehole12, but for other applications as well.

Though often less critically controlled, directional changes in yaw (left-right) may also be necessary to maintain the desired course. When yaw sensing capability is included in beacons26and28, logic much the same as inFIG. 12may be utilized to control the left-right progress of directional boring tool18, wherein their yaw readings (azimuths) would be compared to a Current Azimuth and to a Desired Azimuth.

It is clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While the presently preferred embodiments of the invention have been described for purposes of this disclosure, it will be understood that numerous changes may be made in the combination and arrangement of the various parts, elements and procedures described herein without departing from the spirit and scope of the invention as defined in the following claims.