05/263022

10/09/1973

06/15/1972

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Schlumberger Technology Corporation (New York, NY)

367/84

E21B47/18; E21B47/12; G01V1/40

340/18LD,18NC 175/232,40

Borchelt, Benjamin A.

Birmiel H. A.

What is claimed is

1. Apparatus adapted for transmitting data signals from a well bore to the surface and comprising:

2. The apparatus of claim 1 wherein said second means include an electric motor, and means cooperatively coupling said second member to said motor for rotation thereby as well as for movement between an operating position adjacent to said first member and a solids-clearing position more distant therefrom; and said third means include biasing means cooperatively arranged for yieldably urging said second member normally toward one of its said positions.

3. The apparatus of claim 2 wherein said one position is said operating position of said second member.

4. The apparatus of claim 1 wherein said second means include an electric motor, and means cooperatively coupling said second member for rotation thereby; and said third means include means cooperatively arranging one of said members for longitudinal movement relative to the other of said members between an operating position adjacent to said other member and a solids-clearing position more distant therefrom, and biasing means cooperatively arranged for normally urging said one member toward said other member and yieldable in response to slowing of said second member below said selected speed by fluid-borne solids for allowing said one member to move longitudinally away from said other member.

5. The apparatus of claim 1 wherein said second means include an electric motor, a rotatable shaft drivingly coupled to said motor, means cooperatively coupling said second member to said shaft for rotation thereby as well as for movement therealong between a signal-producing position adjacent to said first member and a solids-clearing position more distant therefrom; and said third means include biasing means cooperatively arranged between said shaft and said second member for normally biasing said second member toward its said signal-producing position and yieldable in response to at least one operating condition characteristic of the rotational slowing of said second member for allowing said second member to move at least momentarily toward its said solids-clearing position.

6. The apparatus of claim 1 wherein said second means include a selectively reversible electrical motor, a rotatable shaft drivingly coupled to said motor, and means cooperatively coupling said second member to said shaft for rotation thereby as well as for movement therealong between a first position adjacent to said first member and at least a second position more distant therefrom; and said third means include biasing means cooperatively arranged between said shaft and said second member normally biasing said second member toward its said first position and yieldable in response to slowing of said second member for allowing said second member to move at least momentarily toward its said second position, and circuit means responsive to the slowing of said second member for selectively reversing the rotational direction of said motor.

7. The apparatus of claim 1 wherein said second means include a selectively reversible electrical motor, a rotatable shaft drivingly coupled to said motor, means cooperatively coupling said second member to said shaft for rotation thereby as well as for movement therealong between a first position adjacent to said first member and at least a second position more distant therefrom; and said third means include biasing means cooperatively arranged between said shaft and said second member normally biasing said second member toward its said first position and yieldable in response to slowing of the rotational speed of said second member for allowing said second member to move at least momentarily toward its said second position, and circuit means responsive to the slowing of said second member and selectively operable for alternately reversing the rotational direction of said motor back and forth so long as said second member is slowed below said selected speed.

8. Apparatus adapted for transmitting data to the surface during the drilling of a borehole and comprising:

9. The apparatus of claim 8 wherein said one member is said flow-obstructing member.

10. The apparatus of claim 9 wherein said first means include motor means; and said second means include control means coupled to said motor means and responsive to slowing of said flow-obstructing member below said selected speed for rotatively moving said flow-obstructing member back and forth in relation to said flow-directing member so long as said flow-obstructing member is slowed below said selected speed.

11. The apparatus of claim 9 wherein said first means include a reversible electric motor; and said second means include circuit means operable upon slowing of said motor means for producing an electrical signal, and control means responsive to said signal for repetitively reversing said motor.

12. The apparatus of claim 9 wherein said first means include a motor, and a rotatable shaft cooperatively coupled to said motor for rotation thereby; and said second means include means co-rotatively coupling said flow-obstructing member to said shaft for rotation thereby as well as for movement along said shaft between a first position adjacent to said flow-directing member and a second more-distant position away from said flow-directing member, and biasing means normally urging said flow-obstructing member toward its said first position and yieldable in response to the occurrence of an operational condition indicative of the lodging of fluid-borne debris between said members for allowing said flow-obstructing member to move at least momentarily toward its said second position.

13. The apparatus of claim 12 wherein said operational condition is an increased pressure differential across said members sufficient to move said flow-obstructing member toward its said second position.

14. The apparatus of claim 12 wherein said second means further include control means coupled to said motor and responsive to slowing of said flow-obstructing member below said selected speed for rotatively moving said flow-obstructing member back and forth in relation to said flow-directing member so long as said flow-obstructing member is slowed below said selected speed.

15. The apparatus of claim 9 wherein said first means include a motor, and a rotatable shaft cooperatively coupled to said motor for rotation thereby; and said second means include means co-rotatively coupling said flow-obstructing member to said shaft for rotation thereby as well as for longitudinal movement along said shaft between a first position adjacent to said flow-directing member and a second more-distant position away from said flow-directing member, and biasing means normally urging said flow-obstructing member toward its said first position and yieldable in response to the occurrence of an operational condition indicative of the lodging of fluid-borne debris between said members for allowing said flow-obstructing member to move at least momentarily toward its said second position.

16. Apparatus adapted for measuring at least one downhole condition while drilling a borehole and comprising:

17. The apparatus of claim 16 wherein said first means include a rotatable shaft coupled to said motor; and

18. The apparatus of claim 16 wherein said signaling member is downstream of said fluid-directing member.

19. The apparatus of claim 18 wherein said first means include a rotatable shaft coupled to said motor; and

20. The apparatus of claim 19 wherein said second means further include means co-rotatively coupling said signaling member to said shaft, and control means coupled to said motor and responsive to slowing of said signaling member below said selected speed for alternately driving said motor back and forth in opposite rotative directions so long as said signaling member is slowed below said selected speed.

21. The apparatus of claim 16 wherein said flow-directing member is fixed in relation to said body and is coaxially arranged in said fluid passage.

22. The apparatus of claim 16 wherein said flow-directing member is upstream of said signaling member.

23. The apparatus of claim 22 wherein said first means include a rotatable shaft coupled to said motor; and said second means include means co-rotatively coupling said signaling member to said shaft for rotation thereby as well as for movement along said shaft between a first position adjacent to said flow-directing member and a second more-distant position away from said flow-directing member, and biasing means normally urging said signaling member toward its said first position and yieldable in response to the occurrence of an operational condition indicative of the lodging of fluid-borne debris between said members for allowing said signaling member to move at least momentarily toward its said second position.

24. The apparatus of claim 23 wherein said operational condition is an increased pressure differential across said members sufficient to move said signaling member toward its said second position.

25. The apparatus of claim 24 wherein said second means further include control means coupled to said motor and responsive to slowing of said signaling member below said selected speed for alternately driving said motor back and forth in opposite rotative directions so long as said signaling member is slowed below said selected speed.

26. The apparatus of claim 23 wherein said means corotatively coupling said signaling member to said shaft include spline-and-groove means between said signaling member and said shaft for allowing said signaling member to move along said shaft between its said first and second positions.

27. The apparatus of claim 23 wherein said means corotatively coupling said signaling member to said shaft include spline-and-groove means between said signaling member and said shaft for allowing said signaling member to move longitudinally along said shaft between its said first and second positions.

28. The apparatus of claim 27 wherein said operational condition is an increased pressure differential across said members sufficient to move said signaling member toward its said second position; and said second means further include control means coupled to said motor and responsive to slowing of said signaling member below said selected speed for alternately driving said motor back and forth in opposite rotative directions so long as said signaling member is slowed below said selected speed.

29. The apparatus of claim 28 wherein said motor is a reversible motor; and said control means include means operable upon slowing of said motor for producing an electrical signal, and means responsive to said signal for repetitively reversing said motor.

Various downhole signaling devices have been proposed heretofore for transmitting data representative of one or more downhole conditions to the surface during the drilling of a borehole. One of the more-promising devices of this nature is a fluid-dynamic transducer or a so-called "siren" (such as shown generally at "62" in U.S. Pat. No. 3,309,656) that is selectively arranged for developing acoustic signals which are transmitted to the surface through the circulating mud stream in the drill string. A typical one of these sirens includes a grooved or ported rotor which is rotatively driven at one or more selected speeds across one or more jets of drilling mud issuing from a fixed groove or ported stator for producing acoustic signals at frequencies related to the design of the siren members, the properties of the drilling mud, and the rotational speed of the rotor. Thus, by selectively controlling the rotational speed of the rotor in accordance with variations in a measured downhole condition, the siren can be selectively operated as required for transmitting coded acoustic signals to the surface which are representative of the measurements of the downhole condition.

Although sirens such as these have other advantages, one of the paramount advantages in using these signaling devices is that acoustic signals can be efficiently produced thereby within a frequency span of about 10 to 300-cycles/second. As noted in the aforementioned patent, frequencies above this range are subject to significant attenuation; and it is, therefore, preferred to operate these sirens to produce signals at frequencies between about 10 to 60-cycles/second. Although signaling devices such as these have shown significant promise for commercial applications, the narrow spacing between the two siren members required to produce satisfactory acoustic signals makes these sirens particularly susceptible to being jammed or easily obstructed either by drilling mud solids or by well debris and the like which is prevalent in the circulating mud stream in a typical borehole.

Accordingly, it is an object of the present invention to provide a new and improved well bore data-transmission system for producing selectively coded acoustic signals in a selected frequency range in debris-bearing well bore fluids such as a circulating stream of drilling mud.

This and other objects of the present invention are attained by providing a well tool adapted to be connected in a pipe string such as a drill string having a drill bit dependently coupled thereto and arranged for excavating a borehole as a drilling fluid is circulated through a fluid passage in the tool and the drill string. To generate distinctive acoustic signals in the circulating fluid representative of one or more downhole measurements, acoustic signaling means on the tool include a selectively controlled electric motor rotatively driving a flow-controlling member arranged to be positioned immediately adjacent to another flow-controlling member within the fluid passage so as to cyclically vary the degree of flow obstruction presented by the two flow-controlling members in cooperation with one another for producing an acoustic signal. The acoustic signaling means further include control means responsive to an operating condition, such as an increased pressure drop across the two members, which is indicative of slowing of the motor for temporarily separating the flow-controlling members so as to allow debris and the like to be carried free of the two members by the flowing mud stream. The control means are further responsive to the cessation of the operating condition causing slowing of the motor, such as a decrease in the pressure differential to its usual operating range, for restoring the flow-controlling members to their signal-producing positions once debris has been freed from between the two members. Means are further provided for selectively reversing the rotational direction of the rotating member as a further aid in clearing debris and other solid materials from the acoustic signaling means.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following description of exemplary apparatus employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIG. 1 shows a new and improved well tool arranged in accordance with the present invention as it will appear while coupled in a drill string during the course of a typical drilling operation;

FIG. 2 depicts a preferred embodiment of the acoustic signaler employed with the well tool shown in FIG. 1;

FIGS. 3 and 4 are cross-sectional views respectively taken along the lines 3--3 and 4--4 in FIG. 2; and

FIG. 5 schematically illustrates a representative control circuit which may be employed in the present invention.

Turning now to FIG. 1, a new and improved well tool 10 arranged in accordance with the present invention is depicted coupled in a typical drill string 11 having a rotary drill bit 12 dependently coupled thereto and adapted for excavating a borehole 13 through various earth formations as at 14. As the drill string 11 is rotated by a typical drilling rig (not shown) as the surface, substantial volumes of the drilling fluid or so-called "mud" are continuously pumped downwardly through the tubular drill string and discharged from the drill bit 12 to cool the bit as well as to carry earth borings removed by the bit to the surface as the mud is returned upwardly along the borehole 13 exterior of the drill string. As is typical, the mud stream is circulated by employing one or more high-pressure mud pumps (not shown) which continuously draw the fluid from a storage pit or surface vessel (not shown) for subsequent recirculation by the mud pumps. It will be appreciated, therefore, that the circulating mud stream flowing through the drill string 11 serves as a transmission medium that is well suited for transmitting acoustic signals to the surface at the speed of sound in the particular drilling fluid.

In accordance with the principles of the present invention, data-transmitting means 15 are arranged on the well tool 10 and include one or more condition-responsive devices, as at 16 and 17, respectively coupled to an appropriate measurement encoder 18 operatively arranged to produce a series of electrical coded data signals that are representative of the measurements being obtained by the condition-responsive devices. Although a self-contained battery power supply could be employed, as shown at 19 it is preferred to employ a reaction-type turbine driving a generator for utilizing the circulating mud stream as a motivating source to generate electric power for operation of the new and improved data-transmitting means 15. As will subsequently be explained in greater detail, the data-transmitting means 15 further include acoustic-signaling means 20 including an electric motor 21 coupled to the encoder 18 and operatively arranged to respond to its coded output signals for rotatively driving an acoustic signaler 22 by way of a typical gear train 23 to successively interrupt or obstruct the flow of the drilling fluid through the drill string 11. The resulting acoustic signals produced by the acoustic signaler 22 will be transmitted to the surface through the mud stream flowing within the drill string 11 as encoded representations or data signals indicative of the one or more downhole conditions respectively sensed by the condition-measuring devices 16 and 17. As these data signals are successively transmitted to the surface, they are detected and converted into meaningful indications or records by suitable acoustic signal detecting-and-recording apparatus 24 such as that disclosed in either U.S. Pat. No. 3,309,656, U.S. Pat. No. 3,488,629, or U.S. Pat. No. 3,555,504.

Turning now to FIG. 2, a cross-sectioned elevational view is shown of a preferred embodiment of the new and improved acoustic signaler 22. As seen there, the tool 10 includes a tubular body 25 which is cooperatively arranged in a typical manner with appropriate end connections (not shown) to allow the body to be tandemly coupled in the drill string 11. The tubular body 25 includes an axial fluid passage 26 for conducting the drilling fluid flowing through the drill string 11 to the drill bit 12 therebelow. As illustrated in FIGS. 2 and 3, the new and improved acoustic signaler 22 includes an annular ported or internally grooved flow-directing member 27 which is coaxially arranged within the flow passage 26 and secured to the body 25 as by a set of complementary threads 28. As will subsequently be explained in greater detail, in the preferred embodiment of the acoustic-signaling means 20 the flow-directing member 27 is provided with a plurality of flow passages defined by inwardly opening longitudinal grooves, as at 29, having a substantially rectangular or square cross-sectional configuration which are respectively cut at equal circumferentially spaced intervals around the interior wall of the flow-directing member parallel to and at a uniform radius from the longitudinal or central axis 30 of the tool body 25. To minimize turbulence and other disturbances to the flow of the downwardly flowing drilling fluid through the tool 10, the upper face of the flow-directing member 27 is concavely shaped as at 31.

As best seen in FIGS. 2 and 4, in its preferred embodiment the acoustic signaler 22 further includes a rotatable ported or externally grooved flow-obstructing member 32 which is cooperatively arranged on the upper end of the output shaft 33 of the gear train 23 and coaxially disposed within the central fluid passage 26 for rotation in a transverse plane of rotation normally lying immediately below the flow-directing member 27. As illustrated in FIG. 2, the opposed lower and upper faces 34 and 35 of the flow-directing member 27 and the rotating flow-obstructing member 32, respectively, are preferably made flat so as to respectively lie in parallel transverse planes which are perpendicular to the longitudinal axis 30 of the tool body 25 and are normally spaced a very close distance apart which, in the preferred embodiment of the present invention, is in the order of 0.020 to 0.030-inches.

As best seen in FIGS. 3 and 4, in the preferred embodiment of the acoustic signaler 22, the exterior of the rotating flow-obstructing member 32 is provided with a number of longitudinal grooves 36 which are cooperatively shaped to define a plurality of equally spaced, outwardly directed radial projections, as at 37, respectively having a substantially rectangular or square configuration. Although different dimensions and shapes, relative numbers, and relative proportions may be used for the grooves 29 and the projections 37 of the flow-controlling members, it is preferable that the rotating member 32 be substantially complementally shaped with respect to the interior opening of the flow-directing member 27. In this manner, when the flow-obstructing member 32 is angularly oriented with respect to the flow-directing member 27 so as to align the projections 37 with the grooves 29, there will be a substantial momentary obstruction to the flow of the circulating mud stream through the tool 10. As pointed out in the aforementioned U.S. Pat. No. 3,309,656, by making the several grooves 29 and the projections 37 substantially square or rectangular, rotation of the flow-obstructing rotor 32 in relation to the flow-directing stator 27 will repetitively obstruct the fluid passage 26 to a substantial degree and then re-open the passage as the radial projections are progressively moved into registration and then out of alignment with the grooves for producing cyclically varying sinusoidal pressure signals in the flowing drilling mud of significant amplitude at the design fundamental frequency. In other words, by virtue of the rectangular or square configurations of the grooves 29 and the radial projections 37, the effective flow area for the drilling mud passing through the tool 10 will vary continuously in a linear fashion so as to minimize the unwanted generation of acoustic signals of significant amplitudes at high-order harmonic frequencies.

Of particular significance to the present invention, it will be appreciated that instead of being fixed to its driving shaft as is the case for the siren disclosed in the aforementioned U.S. Pat. No. 3,309,656, the flow-obstructing member 32 is slidably mounted on the shaft 33 and co-rotatively coupled thereto as by one or more complementary longitudinal splines and grooves, as at 38, which are cooperatively arranged to permit the rotor to also slide longitudinally along the shaft between its normal elevated position as depicted in FIG. 2 and at least one other relatively lower position where the rotor is more distant from the flow-directing member 27. To define the uppermost position of the rotor 32 in relation to the stator 27, the upper face 35 of the rotor is counterbored, as at 39, for complementally receiving an enlarged shoulder 40 on the uppermost end of the shaft 33. Biasing means, such as a compression spring 41 having a predetermined spring force mounted around the shaft 33 between the gear-reduction unit 23 and the lower face of the flow-obstructing member 32, are cooperatively arranged for normally urging the rotating member upwardly toward the flow-directing member 27 so as to normally maintain the opposed faces 34 and 35 of the two members closely spaced under usual flow conditions. As depicted, it is preferred that the lower end of the spring 41 be supported by a fixed shoulder 42 on the shaft 33 and having its lower face slidably engaged with the upper end of the gear-reduction unit 23.

Accordingly, it will be appreciated that the biasing force provided by the spring 41 will be selected to maintain the flow-controlling members 27 and 32 at their desired longitudinal spacing in relation to one another for producing acoustic signals of a desired characteristic during the normal operation of the acoustic signaler 22. However, should there be a downwardly acting force on the rotating member sufficient to overcome the upwardly-directed biasing action of the spring 41, the flow-obstructing member 32 will be moved downwardly along the shaft 33 until such time that the downwardly acting forces on the rotating member are countered by the upwardly acting force imposed by the further compression of the spring.

In the normal course of operation of the acoustic-signaling means 20 of the present invention, the flow-obstructing member 32 will be rotated at a selected constant speed for producing alternating acoustic signals having a waveform dictated by the shapes of the openings 29 and the projections 37 and at a frequency which is determined by the rotational speed of the rotating member as well as the number of the openings and projections. As various borehole conditions being measured by the measuring devices 16 and 17 change during the course of the drilling operation, the data encoder 18 will be effective for controlling the motor 21 so as to produce, for example, signals of different frequencies such as described in detail in the aforementioned U.S. Pat. No. 3,309,656. It will, of course, be appreciated that other signal-transmission modes may also be employed with the data-transmitting means 15. For example, by momentarily operating the motor 21 so as to either retard or advance the rotation of the flow-obstructing member 32, the phase relationship of the resulting output acoustic signal may be selectively varied sufficiently either in relation to previous output signals or in relation to a constant reference signal for producing other forms of distinctive acoustic signals which are also representative of the borehole conditions being monitored by the measuring devices 16 and 17. It will, of course be appreciated that the details of such selective regulation of the motor 21 for driving the flow-obstructing member 32 to provide a given transmission mode are not necessary for an understanding of the principles of the present invention.

Accordingly, in the usual situation, the flow-obstructing member 32 is steadily rotated at a speed governed by the operation of the driving motor 21. So long as the flow-obstructing member 32 is free to rotate with relation to the flow-directing member 27, the acoustic signals produced by the acoustic signaler 22 will be transmitted to the surface by way of the drilling fluid within the drill string 11 for detection and recording by the surface apparatus 24. However, as it is not at all uncommon, debris and the like which is commonly found in a borehole, such as at 13, during a typical drilling operation will be swept to the surface along with the returning drilling mud where significant portions of such debris will be picked up by the mud pumps and discharged into the drill string 11. As a result, those skilled in the art will appreciate that it is quite likely that pieces of wire, sticks, and other solid foreign materials will, from time to time, enter one or more of the grooves 29 in the flow-directing member 27 and must be carried past the rotating member 32 if rotation of the rotor is to continue. However, all too frequently, it has been found that the torque applied to the flow-obstructing member is insufficient to cut or break debris which is spanning the flow-controlling members 27 and 32 at any given moment. Thus, when this situation arises with a signaling device such as that shown in the aforementioned U.S. Pat. No. 3,309,656, the rotor described there will be easily jammed to halt the further operation of that signaling device.

In keeping with the objects of the present invention, however, the new and improved acoustic signaler 22 is cooperatively arranged for operation of a debris-laden drilling mud. Thus, with the acoustic-signaling means 20 of the present invention, should debris such as a piece of wire or a stick become lodged in two openings, as at 29 and 37, which are then aligned and thereby halt the flow-obstructing member 32 in a slightly-advanced angular position where these two openings are then substantially out of registration, the resulting increased pressure differential in the flowing stream of drilling fluid will be effective for longitudinally shifting the rotating member downwardly along its cooperative spline and groove arrangement 38 on the shaft 33 to open an increased flow area for the passage of debris past the acoustic signaler 22. It will be recognized that as the flow-obstructing member 32 moves further away from the flow-directing member 27, the motor 21 will correspondingly turn the rotating member slightly as permitted by the length and rigidity of the piece of debris that is then lodged in the acoustic signaler 22. In some instances, separation of the flow-controlling members 27 and 32 will be sufficient for pulling the piece of jamming debris free of the flow-directing member so that the continuing flow of the drilling mud will be effective for washing the debris out of the acoustic signaler 22 to restore the rotational freedom of the rotating member. Thus, once a piece of debris has been cleared from the acoustic signaler 22, the flow-obstructing member 32 will be freed and the upwardly-directed biasing action of the spring 41 will be effective for returning the rotating member to its normal position immediately below the flow-directing member 27. Thus, the operation of acoustic-signaling means 20 will continue as before until the acoustic signaler 22 again becomes temporarily jammed by additional debris.

It should be further noted at this point that there may well be debris which cannot be dislodged by simply shifting the flow-obstructing member 32 downwardly in relation to the flow-directing member 27. Ordinarily, this would result in a permanent jamming of the acoustic signaler 22 since the continued torque applied by the motor 21 on the piece of debris linking the flow-controlling members 27 and 32 will simply maintain the debris in a jamming position. However, by virtue of the ability of the flow-controlling members 27 and 32 to separate, it will be appreciated that by reversing the rotation of the motor 21, the respective openings, as at 29 and 37, into which the piece of debris has been lodged can be returned into registration with one another for momentarily positioning a piece of jamming debris in a generally parallel relation to the longitudinal axis 30 so as to hopefully permit the correspondingly increased flow of drilling mud to dislodge the debris. On the other hand, should this fail, reverse rotation of the flow-obstructing member 32 will pull the debris in a different direction and hopefully dislodge the debris.

In any event, once the piece of jamming debris has been cleared from the acoustic signaler 22, the flow-obstructing member 32 will be quickly returned by the spring 41 to its usual position immediately below the flow-directing member 27. Once this happens, the acoustic signal will of course, be restored to continue the transmission of data or information signals to the surface. It should be noted that clearing of the debris will also flush away any accumulation of drilling mud solids on the jammed flow-controlling members 27 and 32 which will occur when the two members are halted in a misaligned position.

It will, of course, be appreciated that various circuits can be provided to selectively reverse the driving motor 21 for attaining the objects of the present invention. However, in the preferred embodiment of the data-transmitting means 15 of the present invention, motor control circuitry 43 such as depicted in FIG. 5 is cooperatively arranged for alternately reversing the rotation of the motor 21 back and forth so long as the speed of the motor is below a desired operational level. As shown there, the motor 21 is a two-phase induction motor which is selectively driven in either rotational direction by a conventional two-phase square-wave power supply 44 coupled to typical driver circuits 45 connected to the two windings of the motor. To accomplish the alternate reversals of the motor 21, a typical reversing switch 46, such as a relay or suitable logic gates, is arranged to selectively reverse the leads to one of the motor windings.

To control the reversing switch 46, a typical tachometer 47 is coupled to the shaft 48 of the motor 21 and cooperatively arranged for producing an output voltage which is proportional to the rotational speed of the motor. This output voltage is preferably rectified and filtered, as at 49, and supplied to one input of a comparator 50 having a reference voltage, as at 51, supplied to its other input. The output of the comparator 50 is connected to one input of a gate, such as a NAND gate 52, having its output connected to the input of a counter 53. The other input of the gate 52 is connected to one of the outputs of the power supply 44 to provide a source of pulses. Any selected one of the outputs of the counter 53 is connected to the reversing switch 46.

Accordingly, in normal operation of the signaler 22, the speed of the motor 21 will be sufficient to maintain the output voltage of the tachometer 47 of such a magnitude that there will be no output signal from the comparator 50. This will correspondingly disable the gate 52 so that there will be no output pulses supplied to the counter 53. Once, however, the motor 21 slows such as when the acoustic signaler 22 first jams, the output voltage of the tachometer 47 will drop so as to produce an output signal from the comparator 50 which, in turn, enables the gate 52. Once the gate 52 is enabled, the pulses from the power supply 44 will be supplied to the counter 53. Thus, each time the number of pulses supplied to the counter 53 reach a number capable of producing an output signal at the connected output of the counter, the reversing switch 46 will be energized or activated to reverse the rotation of the motor 21. The pulses will, of course, continue to be supplied to the counter 53 so long as the speed of the motor 21 is below its normal range. This will, therefore, accomplish a second reversal of the motor 21 once there is a subsequent output from the counter 53 which again energizes or activates the reversing switch 46. Thus, reversal of the motor 21 will be repeated at frequent intervals such as every few seconds or so as long as the tachometer 47 indicates that the speed of the motor is below its normal operating speed and accordingly maintains the gate 52 in an enabled state.

Accordingly, it will be appreciated that the present invention has provided new and improved well bore apparatus for transmitting information or data signals representative of one or more downhole conditions to the surface during the course of a drilling operation. By arranging the acoustic-signaling means of the present invention to include a rotating flow-obstructing member which is cyclically rotated in the proximity of the flow-directing member as the drilling fluid is circulated past these members, an acoustic signal of a frequency related to the design of these members and the rotational speed of the rotating member is produced. To prevent debris and the like which is typically carried in a circulating stream of drilling mud from jamming the signaling means, the rotating member is cooperatively arranged flor sliding movement in relation to its supporting shaft to for the flow-controlling members to be separated thereby opening the normal close spacing between the two members a sufficient amount to allow the drilling fluid to wash the debris free of the acoustic-signaling means. Biasing means are cooperatively arranged for restoring the rotating member to its normal position once the piece of jamming debris has been cleared from the acoustic-signaling means.

While only a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.